PLS-CADD

3.1.1 Requesting an Upgrade

Software upgrades are provided exclusively by electronic means. They can be downloaded manually or directly from within the software. In either case, you should use the Help/ Download Upgrade command described in Section 3.1.1.1 to request an upgrade.

3.1.1.1 Downloading Upgrade

If you select Help/ Download Upgrade from PLS-CADD, the dialog box of Fig. 3.1-1 will open. You will first need to request an upgrade code by clicking on the “Send Email To Request Code " button. A code should be E-Mailed to you within one business day. You can then enter the code into the "I have an upgrade code" dialog and the program will download the upgrade automatically. Please note that all upgrade codes expire within one to two weeks so you should promptly download your upgrade after receiving the code.

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

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If you should have difficulty downloading the upgrade from within the software, you may download it manually by following the instructions in the upgrade E-Mail. In this case, you should use the third option “I have an upgrade code and upgrade file” to install the upgrade.

It may take several minutes before the upgrades you are asking for are downloaded. Once they are downloaded, you will be presented with the same installation dialog box as you do with a CD installation as described in Section 3.2. See Section 3.2 for instructions to complete the installation.

5.3.1 Backing up a Model

When selecting File/ Save, you are saving the model currently residing in memory to designated Project.* files. File/ Save has no effect on the contents of the Libraries which the model refers to. The files in the Libraries only get saved when you edit them.

Occasionally, you might want to save in a single file, say Project.bak, the model (i.e. all the Project.* files) as well as the relevant structure, cable and parts Library files. Therefore, Project.bak is a complete record of the information available at the time a model is backed-up. Project.bak is created with File/ Backup. It can be restored on the same or another computer with File/ Restore Backup. Project.bak includes not only files but their complete directory structure. Section K.3 includes additional information regarding the backup command. Using File/ Backup and File/ Restore Backup is the best way to archive or transfer a PLS-CADD project from one computer to another.

When you use File/ Restore Backup, you are given the opportunity to change the name of the directories in which the various files are kept. Note that when restoring, if you choose to overwrite an older existing component library with a new one you may corrupt all your existing models that refer to that database. Restore Backup is a disk function only which does not open the restored model automatically.

We strongly encourage you to create a backup file of your project whenever it is significantly revised or completed.

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

When requesting technical support from Power Line Systems regarding a specific model, you MUST send us a backup file of that model.

5.3.2 Moving a Model and Associated Libraries without Using "Backup"

As mentioned previously, a single PLS-CADD model (complete project) is stored in Project.* files which include pointers to other Library files. In order to move a complete project and its associated Library files from one computer to another or even to a different directory on the same computer you may use the File/Backup and File/ Restore Backup commands as described in Section 5.3.1.

However, there is an alternate simpler way to move one or more than one PLS-CADD projects and their associated Libraries with the WINDOWS EXPLORER so long (THIS IS ESSENTIAL) as all the files share a common base directory and were saved in Version 4.80 or newer. For example, assume that your single project files (Project.*) or all the files of several of your projects (for example Project1.*, Project2.*, etc.) are stored on a network drive, say in the F:\engr\pls\pls_cadd directory or one of its subdirectories and that all of the Library files to which these projects refer to are included in the F:\engr\pls\libraries directory or one of its subdirectories. The directory F:\engr\pls, which is the longest string common to all the Project*.* files and all the associated Library files, is called the common base directory. Now assume that you wish to move all your PLS-CADD projects and associated Library files to your local drive to work on them in the directory C:\models. All you need to do is to simply copy (using the WINDOWS EXPLORER) the entire content of the common base directory F:\engr\pls to your C:\models directory. Then you can run any PLS-CADD model in the C:\models directory and its pointers to the needed Library file will automatically be changed to their new locations in the C:\models directory.

If the files do not share a common base directory, for example if a PLS-CADD model is in F:\engr\pls\pls_cadd but the associated structure, cable or parts files are stored on a different network drive, say G:\components, then the above procedure which globally moves a model and its associated files cannot be used.

To summarize, if PLS-CADD models and all their associated Library files share a common base directory they can be moved around freely so long as their relative positions do not change when moved to a new directory or drive.

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

5.4.1 Windows and Toolbars

As shown in Fig. 5.1-3, several views of your model can be displayed simultaneously. These views are displayed in Profile, Plan, 3-D, and Sheets windows which can selectively be opened with the Windows/ New Window/ ... commands. The windows can be tiled, moved, sized or closed following standard WINDOWS conventions. When several windows are opened simultaneously, the active window, i.e. that in which the various functions apply, is indicated by a solid blue header. As you will discover, some graphics commands work in all windows while others only work in specific views.

Below the menu bar, you will note a line of toolbars. These can be turned on or off with View/ Toolbars. Fig. 5.4-1 shows most of the available tool bars. Shown from left to right are the Standard Toolbar with 6 buttons, the 3D Toolbar with 12 buttons, the Alignment Toolbar with 4 buttons, the Structures Toolbar with 5 buttons, the Sections Toolbar with 4 buttons and the Applications Toolbar that lets you start our optional transmission structures programs. The Annotation toolbar is not shown. Momentarily positioning the mouse cursor over a toolbar icon will display a descriptive "tooltip" in a little window. Positioning the cursor over a menu item or toolbar icon will display a related "toolhint" in the status bar.

5.4.2 Graphics Commands Available in all Views

The view in any window can be modified through the use of the following commands. The commands are available under the View menu and/or by pressing the appropriate function key, and/ or by clicking on the appropriate buttons in the 3D toolbar. Unless you like using function keys, using the buttons is recommended. The graphics commands only affect the currently active window. You also have the option of navigating the various geometry views using a 3-D Connexion input device (3D Mouse) such as the SpaceNavigator (R).

Important note: When you select a particular graphics mode or other engineering function, you will generally stay in that mode or function (for example zoom rectangle function) until you select another function or right-click the mouse. The mouse cursor will often change to let you know what mode or function you are in. There will also be some information in the lower status bar as to what you should do. Remember that the quickest way to get out of a mode or function is to right-click.

Measuring Distances Between Points

In Plan, Profile and P&P sheets views you can measure the distance between any two points on the screen with View/ Distance Between Points. You click on the first point, then drag (rubber band) the mouse to the second point. The distance and its projections are displayed in the bottom status bar. The View/ Distance Between Points command also works in 3-D views provided that the latitude and longitude of your line of sight are a multiple of 90 degrees,

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

5.4.3 Graphics Command Only Available in Profile Views

Changing Aspect Ratio of Profile View

You can change the ratio of vertical to horizontal scales in a profile view by changing the Station Scale Factor and Elevation Scale Factor in the View/ Scales, Rotations, Panning/ Profile View Aspect Ratio menu. Default values of 1 and 10 give you the aspect ratio of 10. Values of 1 and 20 will give you an aspect ratio of 20.

5.4.4 Graphics Commands Only Available in 3-D Views

When you are in 3-D views, you can view the entire line or any portion of it and zoomin on any component from any vantage point. You must first define a line of sight (see Fig. 5.4-1) and then select its longitude and latitude rotations.

Y

Origin of Line of Sight

The origin of your line of sight, which must be an existing terrain point, is determined as follows. First click the View Rotation Origin button on the toolbar. You will see a red circle snap to the closest terrain point as you move the mouse in the 3-D view. Once the red circle is on top of the point that you want to select as your rotation origin, click the left mouse button. The selected point will remain _{Fig. 5.1-1 Line of Sight} as the rotation origin until changed by going through the rotation origin selection procedure again.

5.4.5 Miscellaneous Display Options

A large number of options exist for displaying various graphical or text items in the different views. The best way for you to learn the effect of these options is to experiment with them. Most display options are available under the View/ Display Options/ .. menus and are selfexplanatory. Following are some comments regarding the less obvious display options.

View/ Markers/ Clear markers lets you clear the temporary red markers left to identify TIN triangles selected to create terrain points at given X,Y locations (Section 6.4.5) or to show locations of the shortest distances between cables or between cables and structures as determined by the clearance commands (Sections 11.2.3.2 and 11.2.3.3).

View/ Display Options/ Structure numbers lets you display as Structure Number, either the True structure number (consecutive integers starting with 1 at the line origin), or the text contained in any one of the thirty-two comment fields of the Structures/ Modify dialog box.

View/ Display Options/ Profile View Structure Labels, or a similar menu for plan or sheets views, opens the dialog of Fig. 5.4-2 where you can select what information is displayed above each structure. The Structure comments selection lets you selectively show or hide any of the 32 comment fields of the Structure/ Modify dialog box also available in the Structures Staking Table. The comment fields may be used for construction notes, structure label, or any other purpose.

View/ Display Options/ Text Size, Line width, Styles .. is used if you want to control text and line characteristics (primarily in P&P sheets) or export P&P sheets drawings to a CAD system in DXF format. Fig. 5.4-3 shows some of the choices you have. You can assign the pen thickness, color, style and CAD layer in which various items (ground line, catenaries, structures, etc.) will appear in the CAD systems.

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

View/ Display Options/ Text Position, Orientation and Background gives you a menu of many options regarding the way text is printed in various views. Opaque text background is selected to highlight text displayed over a dark photograph or bitmap.

View/ Display Options/ Show cable attachment points is used to display each cable attachment point as a solid square if that point is assumed to be fixed (i.e. deadend point at the end of a tension section) or as an open circle if that point is assumed to be a suspension point or a point at the tip of a flexible post insulator (i.e. a point on both sides of which the cable tensions are assumed to be equal.

When View/ Display Options/ Show structure - section check bitmaps is enabled, you will see green G's (Good) or red N's (Not good) next to structures and cables. A "G" next to a structure indicates that its strength and insulator swings are OK for the current location and design criteria. A "N" indicates that there is a violation. Similarly, a "G" or "N" next to a cable indicates that the conductor or ground wire in the corresponding tension section meets the cable design criteria or not. When the check bitmap is enabled, the structure and section checking is done dynamically, i.e. it is carried out continuously during idle computing cycles and does not interfere with whatever else you are doing. Dynamic checking is only currently applied to Method 1, Method 2 and Method 3 structures (see Section 8.3 for definitions of Methods 1, 2 and 3) for performance reasons.

View/ Display Options/ Profile View Inset Structure Display is selected if you wish to see outlines of your structure models in all Profile views as shown in Fig. 5.1-2. These outlines can only be shown if their geometry was described in the structure file: this is always the case for Method 4 structures.

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

5.4.6 Display Options for Line and Tension Sections

The colors, number of phases, weather case, wind direction and cable condition (initial, after creep or after permanent stretch from heavy load) which are used to display the line in any view depend on combinations of parameters selected in three dialog boxes. The Line Display Options dialog box (Fig. 5.4-4) is opened with Sections/ Display Options or with Lines/Edit/Info. The Section Modify dialog box (Fig. 5.4-5) is opened with Sections/ Modify. A table of all sections within your model and their display conditions is also available to edit under Sections/Table. This allows editing of the section display data for many sections at once.

5.4.6.1 Colors for Line, Tension Sections, Structures and Insulators

The colors used to display the wires, the structures and the insulators depend on your selections in the Line Display Options dialog box (see Fig. 5.4-4).

The lines used to display the wires can be solid, dashed or dotted. The wires can be represented by catenary curves (the exact mathematical equilibrium) or approximate parabolas. You should only use the parabolas in the rare cases where you are comparing new designs with old manual designs based on parabolas.

In all views, all metallic structures are displayed in grey and all wood structures are displayed in brown if you select Color and texture PLS-POLE and TOWER. Otherwise, the structures are displayed with the color that you select by clicking on the Structures Color button. All insulators are displayed with the color that you select by clicking on the Insulators Color button.

If you select Draw all sections ... in the Section Colors portion of the box, all wires in the entire line will be displayed with the color which you chose by clicking on the Sections Color button. Otherwise (i.e. if you select Draw each section ... ), the wires of each tension section will be displayed for the color which you specify in the Display portion (lower third) of the Section Modify box shown in Fig. 5.4-5 which you reach with Sections/ Modify or what is shown in the last columns of the Section Table.

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

5.4.6.2 Phases Displayed

If you select Draw all phases ... in the Phases Displayed area of the Line Display Options box, all phases (all wires of the set - sets are defined in Section 8.2.1) will be displayed. Otherwise (i.e. you select Draw only the phase ...), only one phase will be shown in each tension section. The phase displayed is that which you select in the lower right portion of the Section Modify box (Phase 1 is selected in the box of Fig. 5.4-5). The option to show only one phase (usually the lower one) is only applicable in cases where you model more than one wire per set. It is sometimes used when printing P&P sheets or to decrease clutter.

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

5.4.6.3 Weather Case, Cable Condition and Wind Direction

If you select Draw all sections for weather case below ... in the Display Weather Case area of the Line Display Options box, all wires will be displayed for the combination of Weather Case, Cable Condition and Wind Direction which you select from lists of available choices. A wind from the left is a wind which blows towards the positive offset direction of the line. A wind from both direction will show simultaneously the positions of the wires with the wind blowing from the left and from the right. This may be used when looking at the line from the top (latitude of line of sight = 90 degrees) in a 3-D window to see the envelope of the wire blowouts. The option to display all sections for the same weather case may be used if you wish to see the entire line under some extreme wind, extreme cold or everyday condition where all wires are at about

the same temperature and are subjected to the same wind and ice conditions.

If you select Display each section as selected in Section/ Modify ... , then all the wires (or the single wire designated by its Phase number) of each individual tension section will be displayed for the condition which you specify for the particular tension section in the Display area at the bottom of the Section Modify box (see Fig. 5.4-5). The wires are displayed for the wind direction which you specify in the Wind from field in the lower right portion of the box. If you do not select Show selected weather case in the Display area of the Section Modify box, you will have access to the Catenary constant and Swing angle fields (they are grayed in Fig. 5.4-5). Then, all wires in the tension section will be displayed for your selected combination of Catenary constant and Swing angle. On the other hand, if you select Show selected weather case, you will be able to pick the combination of available Weather Case and cable Condition for which the wires in the section should be displayed. The option to display each tension section for its own weather case may be used to show the relative position of two wires, for example a very hot conductor over a not so hot distribution underbuild, or an iced conductor above a non-iced conductor. For example, when drawing P&P sheets, you may decide to display the conductors at maximum design operating temperature while ground wires are displayed simultaneously for a cold condition. To display a conductor at very high temperature, you will need to create a fictitious weather case which has that high temperature, as it is assumed that (unless you are in a dynamic rating mode) the wire temperature is that of the ambient weather case. You may also display your wires at any temperature without creating a weather case by simply typing the temperature into the WC pull down menu. For instance if you want to display the conductor at 212 degrees F then you would need to type 212 into the WC pull down menu.

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

5.4.6.4 Multiple Lines

In general, with PLSCADD, you are normally only working with one line referenced to your ground profile. If you use Lines/ Edit, you will be taken to the Line dialog box of Fig. 5.4-6. Highlighted at the top of that box is the name of the line model (which you select in the Name field at the top of the Line Display Options box of Fig. 5.4-4) as well as some summary information: cost of all structures if such information exists in the Available Structures table (see Section 14.3), number of structures, etc. Actually, there is really no need to get to the Line dialog box, unless you wish to deal with multiple line designs on the same profile.

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There are some situations (see Fig. 5.4-7) where you will build different line models on the same alignment. For example, using the optimization technique described in Section 14, you can obtain complete competing designs made out of wood, steel or concrete poles on the same profile. Or, you may be comparing the design of a distribution line before and after adding new communication cables to it as part of a jointuse study. In these cases, you may wish to superpose these designs for comparison. Each individual design is described internally by the type and location of its structures and cables, as well as the sagging conditions of the cables. This information, for each individual design, is stored in a file which has the .don extension. For example, if you click on the Copy button at the bottom of Fig. 5.4-6, you will create a second line, initially identical to the first one, on the same alignment. You can modify this second line and view it on the same profile as the first one as shown in Fig. 5.4-7. If you have more than one line on one alignment, you can select the one you want to work on (the active line) with the Select button and you can chose to display or hide any one of the lines. Structures and Sections operations apply only to the currently active line. You can delete any selected line with the Delete button.

Several line designs, for example variations of one currently saved in the Project.don file, could be saved under different names, say Project1.don, Project2.don, etc. with the Lines/ Save Don File command. Then, at any future time, they could be brought back in with the Lines/ Load Don File command. They would then all show up in the Line dialog box of Fig. 5.4-6.

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

5.4.6.5 Effect of Line Angle on Sags

Without access to true 3-dimensional line modeling such as provided by PLSCADD, sags have traditionally been calculated by using for span length the centerline distance between structures. However, the difference in span length between phases on different sides of an angle structure can lead to visible differences in sags. For example, the ground wires (or the conductors) on either side of Structure # 6 of the Demo line have clearly different sags (Fig. 5.4-8), even though they are installed under the same tension.

5.4.7 Terrain Display Options

There are many options affecting how some terrain features are displayed. Only some of the options are discussed here. These options are included under the Terrain/ Survey Data Display Options, Terrain/ Clearance Line and Terrain/ Side Profiles menus. For example, vertical lines at each terrain point (vertical lines in the Profile view in the lower right quarter of Fig. 5.4-9) can be shown or hidden by checking Display ground point lines or not. Side profiles and required ground clearance lines can selectively be shown or hidden. They are shown in the Profile view in the lower right quarter of Fig. 5.4-9.

In a 3-D view, the terrain can be displayed by: 1) dots representing surveyed terrain points (lower left of Fig. 5.4-9), 2) TIN triangles representing a surface over the terrain points (upper right of Fig. 5.4-9), 3) contour lines determined automatically (upper left of Fig. 5.4-9), 4) color rendering showing elevations, hidden surfaces and light incidence (not shown), or 5) draped photographs (as shown on the cover of this manual). Display options 2) to 5) are selected in the TIN Display Options dialog box by: checking Unrendered triangle outlines for 2), entering Contour line interval of 5 ft for 3), selecting Render triangle, color by elevation, intensity by incidence for 4) and selecting Render triangle, color from bitmap, intensity from bitmap for 5). You should note in Fig 5.4-9 that three 3-D views have been opened simultaneously and the same terrain point is tracked in all four views.

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

5.4.8 Cross-section Views

By selecting View/ Scales, Rotations, Panning/ Cross Section or by pushing the C key you can generate a cross section view (perpendicular or at an angle to the alignment) of all items in your line model located within a certain distance from the reference station of the cross section view. For the Demo line and the selections in Fig. 5.4-10 you can generate the cross section view shown in Fig. 5.4-11.

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

5.4.9 Exporting to Google Earth™

You can visualize your PLS-CADD model in Google Earth to take advantage of that program’s popular graphical environment. This is described in detail in the following technical note:

http://www.powline.com/products/ge_tips.html

Fig. 5.4-12 PLS-CADD Exported to Google Earth

In addition, you may export many reports to Google Earth by right clicking the mouse within the body of the report and then selecting KML export and selecting the particular report in question. It will then prompt you to save the file. After naming the file and selecting Save the program will prompt you to see if you would like to view the report in the default system KML viewer which can be set to Google Earth. This will then automatically launch the Google Earth Viewer and display the particular report selected.

5.4.10 Additional Text and Lines

In addition to what you can see in the various PLS-CADD views, which is derived from the 3-D model itself and its attachments, you can add some graphics and annotations to any view. This is described in Section 13.3. An example of lines and annotations can be seen in the lower left block of Fig. 13.4-1

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

5.5 Latticed Towers Line

Fig. 5.5-1 Profile, Sheets and 3-D Views of WPLFULL Line

Fig. 5.5-1 shows the Profile, 3-D and Sheets views for a latticed tower line that you can load from your PLS-CADD distribution CD as file Wplfullm.xyz. This line, originally built in the 1930's, was recently reconductored and refurbished to almost double its current carrying capacity (Kluge et. al., 1994). It includes 112 steel latticed towers, all modeled with the TOWER program.

If you want to check a particular tower along the profile, simply select Structures/ Check, click on the tower, and watch the Strength Percent Usage appear in the Structure check dialog. Click on the Report button of the Structure check box to get more detailed information. If you select Long you will get a complete TOWER analysis report. If you select Geometry, you will get a deformed geometry window of the tower which you can manipulate to obtain a great deal of graphical information (for example a view like that on the left pane of Fig. 5.5-2). However, in order to manipulate the deformed geometry window and interpret the results within, you should be familiar with the TOWER program.

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

6.1.1 Checking of Required Clearances

Feature codes and the corresponding required clearances allow PLS-CADD to automatically identify clearance violations between wires and survey points for any number of combinations of weather and cable conditions (defined under Criteria/ Survey Point Clearances). In making its checks, PLS-CADD takes into account the voltage of the wires and the required clearances as defined in the Required Vertical Clearance (RV) and the Required Horizontal Clearance (RH) columns of the Feature Code Data Edit dialog. The checking depends on whether RH is a non

zero value (or non-blank).

If RH is non-zero, PLSCADD considers a prohibited rectangular clearance zone (A-B-C-D) about each survey point P as illustrated in the upper left part of Fig. 6.1-3. A-B-C-D is in the vertical plane passing through P and perpendicular to the alignment at that point. If the point is an aerial obstacle, the lower edge of the rectangle (C-D) is located a distance RV below the survey point: otherwise it is on the ground. Any wire that pierces the plan of A-B-C-D inside the rectangle is reported as a clearance violation (with red text in the reports and red markers in the various views). When RH is non-zero,

COK

COK

RV

RVB

RVB

COK

COK

EF

GH

COK

P = SURVEY POINT COK = CABLE POSITION WITHOUT ANY CLEARANCE PROBLEM CNG = CABLE POSITION WITH CLEARANCE VIOLATION C?? = CABLE POSITION WITH POSSIBLE CLEARANCE PROBLEM DEPENDING ON HORIZONTAL DISTANCE TO P

RH = REQUIRED HORIZONTAL CLEARANCE RV = REQUIRED VERTICAL CLEARANCE ABOVE POINT RVB = REQUIRED VERTICAL CLEARANCE BELOW POINT RVB = HEIGHT OF P ABOVE GROUND, OR EQUAL TO RV FOR AERIAL OBSTACLE

CROSS SECTION VIEW THROUGH POINT P PERPENDICULAR TO ALIGNMENT

Fig. 6.1-3 Checking Survey Point Clearances

you normally select “Not a violation“ at the top of the Feature Code Data Edit dialog of Fig. 6.1

2: this is done for the treatment of points that have insufficient vertical clearance but adequate horizontal clearance.

If RH is zero (or blank), the width of the rectangular zone A-B-C-D is no longer defined. The zone is now an horizontal band bounded by an upper line (E-F) and a lower line (G-H) as shown in the upper right part of Fig. 6.1-3. Any wire that pierces the band is reported as a potential clearance violation (with blue text in the reports and blue markers in the various views). Once your attention has been drawn to the potential violation, you will need to look at the situation in more detail to determine if it is an actual violation or not. If RH is zero (or blank), you normally select “Questionable violation ..“ at the top of the Feature Code Data Edit dialog of Fig. 6.1-2. Checking clearances is done with the Terrain/ Clearance or Lines/ Reports/ Survey Point Clearances commands.

6.2.1 XYZ Coordinate System Selection

You should read the following technical note to see how you can designate the coordinate system used in your project for compatibility with other software:

http://www.powline.com/products/coordsys.pdf

6.3.1 Defining or Editing Alignments on Terrain without Existing Line

The alignment functions operate somewhat differently depending on whether there is already a line on the terrain or not. In this section, we show how to create an alignment, or several alignments including branches and loops, when no line exists.

6.3.1.1 Defining or Editing a Single Alignment

For example load the GRID terrain model. Because no alignment has yet been defined on the GRID terrain, the profile view is not yet available. Therefore, the only window which includes useful information is the plan view which shows 13 points. Information about the terrain point closest to the mouse cursor can be seen in the lower status bar.

Our goal is to create a single alignment that starts at Point 1, goes straight to Point 8 and terminates at Point 6. We will eventually generate a centerline profile and four side profiles as shown in the left portion of Fig. 6.3-2. The process shown below is deliberately round-about to illustrate the main P.I. editing commands

Fig. 6.3-3 Add P.I. Dialog Box First click on the Add P.I. button on the toolbar (the one with the red + sign) to start creating a new alignment. Then click on Points 1, 2, 5, and 6 until you see the GRID Alignment 1-2-5-6 of Fig. 6.3-4. Get out of the Add P.I. mode by clicking on the right mouse button. You now have a plan view of your entire corridor with five blue lines following the corridor. The outer pair of blue lines shows the Maximum offset for profile view and the inner pair shows the Maximum offset for centerline ground profile. Both widths are selected in the Terrain/ Terrain widths menu and are discussed in Section 6.3.2.

You can modify your corridor by moving, inserting or deleting alignment points. For example, click on the Move P.I. button, click and hold the mouse button on the third alignment point (Point 5) and drag it to Point 8. Get out of Move P.I. mode by right-clicking the mouse. Now click on the Delete P.I. button and click on Point 2 to get the alignment shown in Fig. 6.3-5. Click the right mouse button to get out of Delete P.I. mode.

Now, click on the Add P.I. button again. Note that this time, the Add P.I. command brings up the Add/ Insert P.I. dialog box shown in Fig. 6.3-3. This is different from when we clicked on Add P.I. the first time because the existence of an alignment gives us some options we did not have before. You can try adding or inserting a

P.I. with each of the options to see the behavior. You can undo the addition/ insertion by selecting Edit/ Undo Terrain/ Alignment/ Add P.I. Again, click the right mouse button to get out of Insert P.I. mode.

When you are done working with the GRID Example, make sure that you do not save it when you quit PLS-CADD as we will re-use the virgin terrain (without any alignment) again with the examples of Section 6.3.1.2.

As an alternate to the manual definition of an alignment using the alignment functions defined above, you can automatically create an alignment through points having specified feature codes with Terrain/ Alignment/ Automatic Alignment.

You can reverse the direction of your alignment, that is flip the corresponding Profile view left to right, with Terrain/ Alignment/ Reverse Alignment.

Whether you create an alignment manually or have one generated automatically through a list of surveyed points, you have the ability to remove PI's with small angle values with Terrain/ Alignment/ Delete Small Angle PI. You enter the maximum angle value and the maximum allowed distance for a structure to move.

6.3.1.2 Defining or Editing Additional Alignments

Once you have at least one alignment defined, you can create: 1) other independent (unconnected) alignments, 2) alignment branches, or 3) alignment loops. These are discussed in the following examples. When you have multiple alignments you can build lines on all of them. These lines will be displayed simultaneously in the 3-D views. Structures at the junctions of several lines will be loaded by all wires attached to them. Additionally, clearances can be measured between all wires regardless of the alignment they are on. To create an independent alignment, branches or loops, click on the New Alignment button or go the Terrain/Alignment/New Alignment to take you to the New Alignment dialog box of Fig. 6.3-6.

Open Branch:

For this example, load again the GRID terrain model (without any alignment on it). Create first the main alignment 1-2-5-13-9 following the procedure described in Section 6.3.1.1 (make sure you click on Point 13 this time). That alignment will appear as shown in the Plan window at the right of Fig. 6.3-8. Then click on the New Alignment button and select Branch and Add to End of Profile in the New Alignment dialog box. Clicking consecutively on points 5 and 8 will create the additional branch 5-8.

After you open a Profile window, you will note that the profile for the additional branch follows, after the specified gap, that of the original alignment because you had selected Add to End of Profile in the New Alignment dialog box.

Loop:

Now continue with the open branch example, click on the Add P.I. button, select Insert After in the Add/ Insert P.I. dialog box, click sequentially on Points 8 and 13, and OK snapping on the existing P.I. at Point 13. You have effectively closed the branch and made a loop out of it. This is shown in Fig. 6.3-9.

You will note that the Profile window in Fig. 6.3-9 is identical to that in Fig. 6.3-8, except that you have added one straight line segment 8-13 to the profile of the branch. Actually, the profile continues in a straight line beyond Point 13. Profiles are always extended for some distance beyond the last alignment point if terrain points exist in that region.

However, for reasons which will be explained later in this Section, creating a loop by closing an open branch at the end of the profile should be avoided as it may cause some stringing problems. Instead, the entire loop should be created from its departure point on an existing alignment to its reconnecting point using the procedure described in the following example.

Load again the GRID terrain model (making sure again that there is no alignment on it). Create first the main alignment 1-2-5-13-9 following the procedure described in Section 6.3.1.1 (make sure you also click on Point 13 this time). That alignment will appear as shown in the Plan window at the right of Fig. 6.3-10. Then click on the New Alignment button and select Branch and Insert After Selected Structure or PI in the New Alignment dialog box. Clicking consecutively on points 5, 8 and 13, and OK'ing snapping on the existing P.I. at Point 13 will create the loop 5-8-13. This is shown in Fig. 6.3-10.

If you compare the Plan windows in Figs. 6.3-9 and 6.3-10, they are identical. However, the Profile windows are quite different. In Fig. 6.3-9, the profile of Loop 5-8-13 is displayed entirely after the gap that follows the profile of the main alignment. In Fig. 6.3-10, the profile of Loop 5-8-13 taken over the position of the profile of the main alignment between Points 5 and 13, and the profile of the main alignment after Point 5 has been moved over to the end of the Profile window. This is because of one imperative rule that you will need to observe for loops because of the way you will string cables to structures in the Profile window (stringing is discussed in Section 10.3).

The rule is: when a loop rejoins an existing alignment at a particular P.I., the profiles of all the paths leading to that P.I. must be displayed before continuing with the display of any profile beyond the P.I. (remember that alignments are directional, i.e. they have stations that increase in the direction in which you have created them). For example, in Fig. 6.3-9, the profile of Segment 13-9 is displayed before the profile of the Loop 5-8-13, which is unacceptable and will cause stringing problems later on. However, in Fig. 6.3-10, the profile of Segment 13-9 is shown at the end of the Profile window following all branches leading to P.I. 13, which is necessary to avoid future stringing problems.

You will understand the need for the rule once you will have learned that structures are spotted in the Profile window and then cables are attached (strung) to the appropriate structures in that Profile window. You always string a tension section by starting at a dead end structure and then you move progressively to the right (you cannot move to the left) in the Profile window in search of intermediate supports, eventually terminating the stringing at another dead end structure. When you have a single alignment, the profile displayed in the Profile window is that of that alignment. When you have more than one alignment, the profiles of all created alignments are displayed in the Profile window as the profile of a single virtual alignment which is used for spotting and stringing structures. In Fig. 6.3-7, the virtual alignment is 1-2-5-9-gap-4-12-8 (the portion 9-4 is not real and is represented by a gap). In Fig. 6.3-8, the virtual alignment is 1-2-513-9-gap-5-8 (with a gap between points 9 and 5). In Fig. 6.3-9, the virtual alignment is 1-2-513-9-gap-5-8-13. Finally, in Fig. 6.3-10, the virtual alignment is 1-2-5-8-13-gap-5-13-9.

To summarize what we have learned about branches and loops, we will look at three more examples in Fig. 6.3-11. The squares (or pairs of squares) in the figure represent structures at the end of tension sections (dead ends) and the open circles represent intermediate structures (not dead ends). The numbers shown (ignore the numbers in parentheses at this time) are the internal structure numbers, numbers automatically assigned by PLS-CADD in the order in which the structures appear in the Profile window, i.e on the profile of the virtual alignment.

The sketch at the top of

12

Fig. 6.3-11 represents a 11 main line with two taps. 1 2 3 4 ₅ 6 7 8 The alignment of the main line was created first INITIAL PROFILES OF TWO OPEN BRANCHES ARE (initial alignment), and ^{ALIGNMENT 9}

DISPLAYED AT END OF MAIN PROFILE

10 then two open branches BRANCH OR

were added (and ^LOOP _{2 3} ( 4 ) 8 (5 ) 9 ( 6 ) 10 ( 7 )11 ( 8 ) 12 ( 9 )13 ( 10) 14

displayed at the end of ¹ the main line profile) as

456 7

was done with the example of Fig. 6.3-8.

DEAD END LOOP INSERTED AFTER STUCTURE # 3

NOT DEAD END 1

The sketch in the middle

of Fig. 6.3-11 represents ² _{( 3 ) 5} ( 4 ) 6 ( 5 ) 7 a double circuit line with ( ) STRUCTURE NUMBER its circuits split on ^{BEFORE STRUCTURES 3 4} separate alignments at ^{ARE ADDED IN LOOP}

_{Structure # 3 and then} LOOP INSERTED AFTER STRUCTURE # 2

rejoined them again at ^{Structure # 12 (in the} Fig. 6.3-11 Spotted Structures on Various Alignments following discussion we will use the notation # i to denote Structure # i). A main alignment was created first (following the top branch). In this example, ten structures (# ' s 1, 2, 3, (4), (5), (6), (7), (8), (9), and (10) ) were first spotted on that main alignment before the bottom loop was added. Then the alignment for the bottom loop was created as was illustrated with the example of Fig. 6.3-10. This bottom loop was automatically inserted before the top branch in the virtual alignment. Therefore, as structures were added to the bottom loop, their numbering system started with the number 4. Each time one structure was added to that bottom loop, the internal number of the structures in the top branch and all the structures to the end of the line were automatically incremented by one. Once all four structures were spotted in the bottom loop, the numbering scheme for all structures in the tension sections became those shown without parentheses in the figure. It was then possible to string each circuit separately. For example, the top circuit was strung from # 1, attaching at # 2 and #3 , passing over # 4 to # 7, attaching at # 8 to # 13 and ending at # 14. The bottom circuit was started at #1, attaching at # 2 to # 7, passing over # 8 to # 11, attaching at # 12 to 13 and ending at # 14. Note that the sequence of structures which are attached or bypassed is complete and in ascending order.

The sketch in the bottom part of Fig. 6.3-11 represents a tension section in a main line initially defined along the alignment following # ' s 1, 2, (3), (4) and (5). A distribution tension section that starts on a different alignment somewhere to the left of # (3) and joins the main line as underbuild at # (3) needs to be strung. If the distribution circuit were dead-ended at # (3), then we could simply create an open branch to the left of # (3) and string one tension section along that branch through structures that would be numbered 6 and 7. Another tension section would be strung from # 3 to # (5). However, because the distribution is not dead ended at # (3), it is necessary to make the distribution branch part of a loop that starts somewhere before # (3). We arbitrarily started the loop at # 2 and closed it at # (3). As the two distribution structures # 3 and # 4 were added, the structures in the main line were renumbered 5 to 7 as shown. Then the distribution could be strung from # 3, attaching to # 4, #6, # 7 and ending at # 7.

6.3.2 Maximum Offsets and Center Line Profile

Values for the Maximum Offset for Profile View (MOPV) and the Maximum Offset for Centerline Ground Profile (MOCGP) are selected with Terrain/ Terrain widths.

All ground or obstacle points within the MOPV (measured from the center-line) are displayed with the appropriate symbols in the various profile views, whether on

_{screen or on a sheet of paper.} PLAN VIEW OF THEORETICAL GROUND PROFILE LINE

Points outside the MOPV are not displayed in the Profile views. In addition, any structure or wire with an offset greater than MOPV will not be shown in the profile view. PLAN VIEW OF SELECTED GROUND PROFILE LINE

Once you have an alignment defined on an XYZ terrain model, you can create an equivalent PFL model by using the File/ Save as

^{command and specifying a .pfl} Fig. 6.3-12 Definition of Centerline Ground Profile

extension that tells the program that model should be saved as a PFL file. If you create a PFL model this way, points that cannot be projected on the alignment will be lost. These points are located outside the angle formed by the two lines perpendicular to the alignment at a P.I. and on one side of the alignment. We generally do not recommend that you save an XYZ file with its alignment as a PFL file.

The center-line is defined in the plan view as the collection of straight line segments connecting alignment corners. The center-line ground profile is theoretically the intersection of vertical planes going through the center-line and the ground. However, because the terrain data are only defined at discrete points within the line corridor, there is a need for rules to define how the profile is displayed on the screen and on drawings. The ground profile line displayed by PLSCADD is a line that joins all ground points within a specified offset from the center-line. That offset (MOCGP), is shown in Fig. 6.3-12 for two widths. The points are joined in ascending order of stations. For example, if one selects a MOCGP of 10 ft, then the profile line will pass through all the points within 10 ft of the center-line. If there is significant side slope (perpendicular to the line) the line profile may look jagged when it joins points of significantly different elevations on alternate sides of the center-line. If the jaggedness of the profile line is objectionable, one may draw separate side profiles as described later in this section. Or better, one may generate additional interpolated center line and side profile points using the Triangulated Irregular Network (TIN) model of the terrain as described in Section 6.4. To illustrate the effect of selecting various MOPV and MOCGP values on the profile line corresponding to the alignment in Fig. 6.3-5, open a profile view with Window/ New Window/ Profile View and tile both the plan and profile windows using Window/ Tile Vertical. Your screen should look like Fig. 6.3-13 for a MOPV of 50 ft and a MOCGP of 10 ft (the default values). The profile on the left of Fig. 6.3-13 is for an aspect ratio of 10. The aspect ratio of an active profile view can be changed with View/ Scales ../ Profile View Aspect Ratio. Note that this command is only available if the Profile view is your active window. You will note that the profile is flat between Points 1 and 8 because there is no intermediate point within an offset of MOPV between these two points. The profile is obviously not correct but it is consistent with the scarcity of ground points in the XYZ model. You will also note that nearby points (Points 10 and 12) are not visible in the profile view because they are outside the MOPV.

To get the views of Fig. 6.3-14, change the MOPV to 300 ft and the MOCGP to 200 ft in Terrain/ Terrain Widths. The profile line is no longer flat between points 1 and 8 and some distant points (Points 4 and 5) are now visible. However, the profile line is still far from correct. As will be shown in Section 6.4, a TIN model of the terrain will be used to produce the best possible profile for the given data as shown on the left portion of Fig. 6.3-2.

6.3.3 Editing Alignment when there is a Line on the Terrain

If a line model already exists, you should be careful when Inserting NEW POSITION FOR an alignment point off the current

STRUCTURE # 4

centerline, as you will no longer have a structure at that alignment point and you will no longer have the same span lengths between the two alignment points on either sides of the one you inserted. However, you can select any structure, move it and make an alignment point out of it. You can also add an alignment point at the end of the line. Whether you insert a new alignment point or make an alignment point out of a moved

BEFORE STRUCTURE MOVE structure, the connectivity between cables and structures of _{Fig. 6.3-15 Moving a P.I.} the present design is preserved, but not the span lengths. The connectivity can only be changed with the Sections/ Modify command. With the Move P.I. command, you are able to select an existing structure and drag it to a new location that becomes a new alignment point. For example, in Fig. 6.3-15, Structure #4 was selected and moved to a new location. The center-line between the start of the line and Structure #2, and between Structure #5 and the end of the line are not affected by the move. However, the center-line between Structure #2 and Structure #5 is changed. Structure #3 (a tangent structure) follows the move of Structure #4 in such a way that its distances to the alignment points at Structures #2 and #4 remain in the same proportion before and after the move. After a structure is moved, you should check your design in a profile view.

With the Delete P.I. command, you can click on a structure at an existing alignment point and remove it from the alignment, i.e. make it a tangent structure on a straight line between the previous and next alignment corners.

For example, load the Demo line by selecting the Demo.xyz file. Tile the plan and profile views as shown in Fig. 6.3-16. Small squares show where existing structures in the line are located. Larger squares indicate current alignment points. You should be able to see six grid points in the quadrant to the right and above Structure # 6. Any one of these six points can be snapped onto in order to relocate the line in the quadrant.

If you want to re-route the line so that the alignment passes through point FICT6 (top right point), select Move P.I., click on Structure # 6 and drag it to ground point FICT6 (Fig. 6.3-17) and then release the mouse button Because the demo.xyz terrain does not have any point within the MOCGP along the new corridor between Structures # 3 and # 10, the profile along that new corridor is made up of long straight line segments.

You will note that the number of structures and spans between Structure # 3 and Structure # 10 is preserved. If you were to use File/ Save (don't do this or you will need to re-install the examples), the Demo line design would be updated in such a way that the terrain and design are unchanged before Structure # 3, but the terrain and spans between Structures # 3 and 10 would be new. Remember: Do not save any of the changes you make to the Demo example or any other example or you will need to re-install them if they are to appear as described in this manual.

You can use Edit/ Undo Terrain Alignment/ Move P.I. to bring back the Demo line from its state in Fig. 6.3-17 to that in Fig. 6.3-16.

6.4.1 Triangulated Irregular Network (TIN)

The XYZ terrain model used by PLS-CADD consists of individual points with their coordinates and feature codes. The Triangulated Irregular Network (or TIN) model of the XYZ terrain is a surface made up of triangles having the terrain points at their apexes. PLS-CADD can automatically create the TIN model of an XYZ terrain using Delauney triangles. For example, Fig. 6.4-1 shows the TIN model of the XYZ terrain of the Demo line near Structures # 5 and 6. The primary advantage of a TIN model over the basic XYZ model is that it is a surface and not a collection of points. That surface can be used to generate accurate center line and side profiles, to find the elevations of arbitrary points or to locate points at the intersection of latticed tower legs or guys with the ground. The TIN surface can be rendered in different colors to give a more realistic display of the ground, including elevations and light incidence (Fig. 6.4-3). Bitmaps (aerial photographs) can be projected onto it to give an even more realistic appearance of the terrain (Fig. 6.4-3).

6.4.2 Creating, Saving, Loading or Deleting a TIN Model

The TIN model shown in Fig. 6.4-1 was created by first opening the demo.xyz file, maximizing a Plan or 3-D view to be able to see the triangulation process, and going to the Create Tin Model dialog box with Terrain/ TIN/ Create TIN. In the Create Tin Model box we chose to visualize the progress of the triangulation and to exclude points with zero elevation, and we selected 300 ft for both the maximum offset and the maximum triangle edge width. The triangulation proceeds as soon as you click on OK at the bottom of the Create Tin Model box. In order to see the final result of the triangulation you must be in a Plan or 3-D window and check the Unrendered triangle outline option under Terrain/ TIN/ Display options. Displaying TIN triangles or rendering the TIN model is specific to a particular window. For example, the TIN triangles can be displayed in one window (see right of Fig. 6.4-2) and not displayed in another window (left of Fig. 6.4-2).

Once you have created a TIN model, you can optionally save it in the Project.tin file using the Terrain/ TIN/ Save TIN and reload it in memory at a later time with Terrain/ TIN/ Load TIN.

You can use Terrain/ TIN/ Delete TIN to remove the TIN model from memory. When working on a slow computer with insufficient memory it may be advantageous to delete the TIN model once it is no longer required (when TIN display and cutting new profiles are no longer needed).

6.4.3 Displaying TIN Model

Using the Terrain/ TIN/ Display options menu, you can select several options to visualize the TIN model. These options may not work if your video card does not have the ability to display 256 colors simultaneously. 16 bit color (65536 simultaneous colors) is recommended if draping bitmaps.

Fig. 6.4-3 shows the effect of choosing certain options in the TIN Display Options box:

1) Unrendered triangle outlines (upper left corner) 2) Contour lines interval of 5 ft (upper right corner) 3) Rendered triangles - Color by elevation, intensity by incidence (lower left corner - original

is in color even though Fig. 6.4-3 is black & white) 4) Rendered triangles - Color by bitmap, intensity by bitmap (lower right corner – this requires that a bitmap be attached to the plan view as described in Section 6.5)

6.4.4 Creating Interpolated Ground Points

One of the powerful uses of a TIN model is the generation of terrain points which are located on the center line and side profiles. For example, open the grid.xyz file, define a 1-8-6 alignment as described in Fig. 6.3-5, and create a TIN model excluding points with offsets larger than 1000 ft and deleting triangles with sides longer than 1000 ft. If you chose to display the unrendered triangles, they will appear as 16 green triangles as seen on the right side of Fig. 6.3-2. At this point, your XYZ terrain consists of only 13 terrain points and the associated TIN model consists of 16 triangles.

Now click on Terrain/ TIN/ Create interpolated points, select 200 (typical ground point) for the feature code of the new interpolated points, ask to create interpolated points at offsets of -40 ft, 20 ft, 0 ft, 20 ft and 40 ft, and ask to create these interpolated points only on triangle legs shorter than 1000 ft and with an elevation change of less than 1000 ft. You will note that 57 new points are added to the XYZ model. You can track these points with the mouse or see them with Terrain/ Edit/ Edit XYZ. These so called TIN points, with the description TINPT, are located at the intersections of the sides of the triangles and vertical planes passing through the center line and at offsets of -40, -20 , +20 and +40 ft from the center line. Now your XYZ terrain consists of 70 points, the original 13 plus the additional 57 located within 40 ft of the centerline.

Now go to the Terrain/ Terrain Widths dialog and set MOCGP to 1 ft and MOPV to 50 ft. Go to the Terrain/ Side Profiles table and set the values as shown in Fig. 6.4-4.

If you open a Profile window using Window/ New window/ Profile, you will see colorcoded center line and side profiles as displayed on the left side of Fig. 6.3-2. These are accurate centerline and side profiles for the grid.xyz terrain. They are certainly better than those shown in Figs. 6.3-13 and 6.3-14.

6.4.5 Adding XYZ Points

The TIN model can be used to create XYZ terrain points with selected combinations of X and Y coordinates. For example, select Terrain/ TIN/ Add point at X,Y and click on the location in the plan view where you want the point to be created. A dialog box will let you edit the X and Y coordinates of the point which you have selected, its feature code and the height of the obstacle (if any is located at the point). The created point will be on the surface of the TIN model, i.e. its elevation will be computed at the intersection of the vertical line at the X, Y location with the TIN triangle (shown in red) at that location. If there is no TIN available you will be prompted for the Z value. You can turn off the red highlighting of the triangle with View/ Markers/ Clear Markers or the F5 key.

Several options are available for defining/editing break lines:

1) Use Terrain/ Break Lines/ Import Break Lines from DXF Attachment to create break lines from line and polyline entities in an attached DXF file. Since most commercial terrain modeling packages can export their break lines to DXF this is a very quick and easy way to import their break lines.

2) Use Terrain/ Break Lines/ Import Break Lines from SiteWorks File to read points in from a SiteWorks® file. The format of this file is described in the dialog box which appears when this option is selected from the menu.

3) Use Terrain/ Break Lines/ Load BRK File to load an externally created break line file. See Appendix D for details on the file format.

4) Use the Add or Delete Break Line commands under the Terrain/ Break Lines menu to interactively add or delete break lines. The Add Break Line command will automatically snap to the closest XYZ point so you will need to create XYZ points for your break line end points if they don’t already exist. To create a string of break lines you need only click on XYZ points in the order you want to connect them. To terminate a string and start a new one simply press the Enter key. For example, to create two strings use Add as follows. Click on the origin of the first break line string, click successively on each end of its adjacent segments, and terminate the sequence by pressing the Enter key. Then click on the origin of the second string, click successively on the ends of each of its contributing segments and press Enter. Then right click the mouse to get out of the Add Break Line function.

6.5.1 Using Break Lines to Enhance XYZ Terrain Models

To illustrate the interactive use of break lines to enhance an XYZ terrain model, we will work with the simple 14 point terrain (called BREAK.XYZ) provided on the Examples diskette. The model describes a highway embankment built above the original ground. Points A, B, E, F, AM, AT, BT, ET and FT are on the original ground and points C, D, CM, CT, and DT are surveyed points along the edges of the highway embankment.

Using the functions described in Section 6.4.2 and deleting only triangles with legs larger than 10,000 ft, we get the TIN model shown in Fig. 6.5-1. Contour lines displayed at 2 ft intervals show that the various TIN triangles do not provide a realistic representation of the highway embankment. This is because there are not enough surveyed points along the base and top edges of the embankment. A profile cut across the triangles of Fig. 6.5-1 will not be correct.

But if we now create: 1) a break line segment between B and BT, 2) a break line string between C, CM and CT, 3) a break line segment between D and DT, and 4) a break line segment between E and ET, then the TIN model is enhanced as shown in Fig. 6-19, with 2 ft contour lines displayed parallel to the embankment edges. Profiles cut across the triangles of Fig. 6.5-2 will be correct.

Once the break lines are defined, PLS-CADD can re-triangulate the terrain in their vicinity so that

triangle edges always coincide with the break lines. This is done as if new XYZ points were added at selected locations along the break lines.

6.5.2 Using Break Lines to Describe Existing or Planned Facilities Fig. 6.5-3 shows a portion of a larger terrain described by over 80,000 break line segments and an even larger number of XYZ points. Some of the break lines correspond to yet un-built but planned road improvements.

Fig. 6.5-4 shows the TIN model of the terrain in Fig. 6-20, from which the detailed center line and side profiles were generated.

6.6.1 DXF Drawings

DXF drawings, with the .dxf file extension, are normally generated in a CAD or mapping system. They can be attached and overlaid to plan or profile views using Drafting/ Attachments/ Attachment manager which opens the File Attachments box shown in Fig. 6.6-3. When attached to a plan view, the X,Y coordinate system (Z is elevation) used to describe the DXF drawing should be the same as that used to describe the PLS-CADD XYZ terrain points. When attached to a profile view, the X and Y coordinates of the DXF drawing should be the same as the stations and elevations of the PLSCADD alignment. When attached to a P&P sheets view, the X,Y DXF coordinates should coincide with the local x and y coordinates of a single page (zero at lower left corner of page,

x to right and y up). Once a drawing is attached, you can show it or hide it by clicking on the appropriate button at the bottom

of the File Attachments box. When you Save a project, all attachment information is saved in the Project.don file. Therefore, when you re-open an existing project, it appears with all its attachments.

Once a DXF drawing is attached for the first time, you are taken directly to the DXF Overlay Options dialog box (not shown in this manual). If a DXF has already been attached, you can get to the DXF Overlay Options box by clicking on the Options button at the bottom of the File Attachments box (Fig. 6.6-3).

The DXF Overlay Options dialog box lets you select: 1) whether your attachment should be overlaid on top of Plan or Profile or Sheets views, 2) which units have been used to generate the DXF data, and 3) which layers of the DXF drawing should be displayed. If, when you OK the DXF Overlay Options box, the Advanced transformation check box is checked, you are taken to the DXF Advanced Transformations table shown in Fig. 6.6-4.

In most cases you should simply exit the DXF Advanced Transformations table by clicking on OK. In some cases you might find the need to translate the DXF drawing parallel to the X, Y or Z directions, rotate it about the X,Y, or Z axes, or expand or contract it in any of the three directions. You can enter a series of translations, rotations and scales in the table.

However, rather than using the DXF Advanced Transformations table, the most common adjustments to a DXF can easily be accomplished with the following two commands:

Drafting/ Attachments/ Move lets you slide the entire DXF drawing without any rotation so that the first point which you select on the DXF coincides with a second point which you select on the plan view.

Drafting/ Attachments/ Stretch lets you adjust the entire DXF drawing so that two selected points on the DXF coincide with two corresponding points on the plan view. This should only be made for slight stretching adjustments.

6.6.2 Raster Images

Like DXF files, raster images or bitmaps in BMP, TIFF, JP2 or ECW formats can also be attached to a plan, profile or sheet view. Raster images in other formats such as SID and others can be converted to one of the supported formats using inexpensive paint programs such as Paint Shop Pro. Additional information regarding working with image attachments can be found in our technical note:

http://www.powline.com/products/photos.html

The bitmap (BMP) format is the standard WINDOWS representation of a raster image. It supports only minimal compression (lossless) and will result in very large file sizes. However, almost all WINDOWS programs can read and write BMP files. TIFF (Tagged Image File Format) is an alternate raster format that has wide acceptance and substantially better compression (typically lossless) than BMP files as well as much more flexibility in terms of the bit depth that the images may be saved in. Therefore, TIFF files can be much smaller than the equivalent BMP file. PLS-CADD also supports the GeoTIFF variant of the TIFF format. ECW is a proprietary image file format developed by ERMapper ( http://www.ermapper.com ). ECW offers extraordinary compression frequently achieving compression ratios of 25:1 or even greater. This compression is lossy; however, image degradation can be controlled by the user and is normally insignificant. The JP2 format is discussed in the above-mentioned technical note. PLS-CADD can convert a TIFF, BMP or JP2 file to an ECW file using the ECW button in the Attachment Manager in Fig. 6.6-3.

We recommend the use of ECW files for aerial photography and TIFF files for scanned P&P sheets. Regardless of which format is used, PLS-CADD will internally need to convert the image to a bitmap in order to draw it, so your computer should have as much RAM as you can afford. If you have a large quantity of aerial imagery, PLS-CADD will be most efficient if that imagery is stored in ECW files.

When attached to Plan views, raster images are attached in the same manner as DXF files except that you will be taken to the Bitmap Options dialog box (Fig. 6.6-5). The Bitmap Options box lets you select: 1) whether to overlay the raster image on top of Plan, Profile or P&P sheets view, 2) the X, Y and Z coordinates of the upper left corner of the image, 3) the image width and height in survey units, and the rotation angle around the upper left corner of the image.

In some cases the values of the coordinates of the upper left corner of the bitmap, the bitmap height and width, as well as the bitmap rotation angle can be determined automatically. One such case is when you are attaching a scanned Plan & Profile sheet for digitizing purposes as described in Section 6.8. In such a case the required values are calculated automatically as part of the calibration process. Another case where PLS-CADD fills-in the values automatically is when you are working with aerial photography and have a world reference file such as a TIFF World File. These files contain georeferencing information such as the resolution and location of the image. PLS-CADD identifies a World File by its file extension. The World File must have the same base name as the image and one of the following extensions: ".TFW", ".BFW", ".JDW" or ".SDW". Whenever an image is attached, PLS-CADD will look for a World File with the same base name and in the same directory as the image. If PLS-CADD finds a World File, it will attempt to read it and fill-in the values automatically. PLS-CADD does support the GeoTIFF standard and will read georeferencing information directly from a GeoTIFF.

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008 By default (can be overridden in F1 key menu) raster images are not shown in 3-D views since they are inherently 2-dimensional with the Z coordinate of each pixel unknown.

If the Hide option in Fig. 6.6-3 is selected for a bitmap when the project is saved, that hidden bitmap will not be loaded in memory when the project is re-opened, even though it will still be listed in the Attachment Manager dialog. The bitmap will only be loaded in memory once you change the option to Show.

Important note: Because bitmaps occupy large amounts of memory, judicious use of the Hide and Show options lets you handle cases where it is not feasible to have all attached bitmaps resident in memory at the same time.

You can use Drafting/ Attachments/ Image Drawing Options to control the appearance of your images.

6.6.2.1 Draping of Raster Images on Top of TIN Model

If a digital terrain model (TIN) is available, the program can compute the Z coordinate of each pixel and drape the image over the terrain as shown in the lower right corner of Fig. 6.4-3.

6.6.3 Miscellaneous Attachment Options

There are several options under the Drafting/ Attachments menu that allow you to download imagery from other sources and to control the appearance of the attached pictures. You should consult our technical notes on our web site for additional useful information. For example, to import imagery into PLS-CADD you can consult the following technical notes:

http://www.powline.com/products/usgs2.html

http://www.powline.com/products/coordsys.pdf - This note describes the TerraServer Image Download command which will automatically download the aerial photography and topo maps if the coordinate system is defined.

6.8.1 Opening a Profile View

Importing and displaying a scanned profile drawing should be done in a Profile view. If this is a new project, use File/ New to name the project file, say Project.pfl, create or import some existing feature codes with Terrain/ Feature Code Data/ Load FEA File, open a profile view with Window/ New Window/ Profile. You will get a blank Profile view. If there are already some data in the Project.pfl file, open it and display the Profile view.

6.8.2 Attaching Scanned Drawing to Profile

This is done with the Drafting/ Attachments/ Attachment manager where you specify that the bitmap should be attached to the profile view (not the plan view) and you select the approximate station and elevation of the top left corner of the bitmap (Point A in Fig. 6.8-1), the approximate bitmap width, BW, in station units, and the approximate bitmap height, BH, in elevation units. At this stage (Fig. 6.8-1), the horizontal axis of the profile drawing may not coincide with the horizontal edge of the bitmap due to poor positioning of the drawing when it was scanned. Also, at this stage you do not worry about exactly matching the scales of the drawing and those inherent in your current profile view. If you do not see the bitmap, it may be outside your current viewing area. Click on View/ Initial to get a complete view of your project from which you can zoom-in on the particular bitmap.

6.8.3 Scaling and Orienting Scanned Drawing

This is done with the Drafting/ Attachments/ Calibrate Sheet menu.

You will be asked first to click on the left and on the right of a station line (Points B and C in Fig. 6.8-1) and input the true stations of these two points if True Stations is selected in the Stations Displayed part of the Preferences dialog box of Fig. 5-4. You can input the equation stations of

74 PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008 the two points if: 1) Equations Stations is selected in the Preferences dialog box, and 2) unambiguous relationships between true stations and equation stations have already been defined in the Station Equations table (see Section 6.11). A station line is any line parallel to the station axis of the drawing, i.e. points B and C should have the same elevation. The station line does not have to physically coincide with the line labeled with stations. To improve accuracy, points B and C should be selected as far away from each other as possible. The program will use the information you input for points B and C to: 1) rotate the drawing so that line BC is parallel to the station axis in the profile view and 2) scale the drawing to match the scales used to display terrain points in the profile view. If the required rotation is small, you will be given the choice of neglecting it to reduce redraw time.

Next you will be asked to click on the lower end and on the upper end of an elevation line (Points D and E in Fig 6.8-1) and input the elevations of these two points. An elevation line is any line parallel to the elevation axis of the drawing, i.e. points D and E should have the same station. To improve accuracy, select points D and E as far apart as possible. The elevation information at points D and E will be used to match the vertical scales of the scanned drawing and the profile view.

6.8.4 Sliding Scaled Attachment

Once a drawing is properly scaled, you can always slide it with the Drafting/ Attachments/ Move command. You will be asked to click on any reference point on the attached drawing and then click on where this point should be in the profile view. For example, you can slide the drawing so that a particular point near the left edge of that drawing matches a selected point in the profile view, for example the same point near the right edge of the previously attached scanned drawing.

6.8.5 Creating PFL Points

Once a drawing is scaled and accurately positioned in the profile view, you can click on desired terrain, structure and conductor points to create PFL terrain points at these locations. This is done with the Terrain/ Edit/ Add PFL Points command. A small box appears at the top left of the screen (see Fig. 6.8-2) where you select the feature code, description, offset, line angle and a profile comment for the point being created. If you make a mistake, you can always remove a point with the Terrain/ Edit/ Delete PFL Points.

6.8.6 Creating Line Model

Once you have PFL ground, structure or conductor points on the screen (visible with the appropriate feature code symbols at positions indicated by vertical lines in Fig. 6.82 you can use the standard PLS-CADD commands to build the line by adding structures, stringing and sagging cables (see Section 10).

You can automatically spot structures and snap their conductor attachment points to designated PFL points as described in Section

10.2.5.2.

You can sag sections to match catenary curves of the scanned drawings or to pass through designated PFL points as described in Section 10.3.2.4.

6.9.1 XYZ to PFL Conversion

Assume that you have defined an alignment on top of a Project.xyz terrain. You can create the equivalent PFL model by first going to the Terrain Origin box (Fig. 6.9-1) with the Terrain/ Edit/ Edit Origin command, where you will select the true station of the first alignment point. Then use File/ Save as to save the project with the Project.pfl name. The program will understand from the .pfl extension that the terrain should be saved as a PFL model.

6.9.2 PFL to XYZ conversion

Assume now that you have a PFL terrain model Project.pfl and want to create the equivalent XYZ model. First you should provide the Azimuth of first point plus the X and Y coordinates of the point with zero station in the Terrain Origin box. The azimuth (bearing) is the clockwise angle of the first alignment leg measured from the Y axis. Then use File/ Save as to save the project with the Project.xyz name. The program will understand from the .xyz extension that the terrain should be saved as an XYZ model.

6.10 Side Profiles, Clearance Lines, Prohibited Zones and Special Cost Zones

The collection of straight line segments making up the center line ground profile was defined in Section 6.3.2 and displayed in Fig. 6.3-12.

7.1.1 Modeling of Wire System

One of the most complex parts of a transmission line is the wire system (conductors and ground wires) in a tension section (from one dead end structure to the next dead end structure). Questions arise regarding: 1) the handling of wind load which may not be uniform over the length of the section (wind on individual spans may be larger than the average wind over the section because of varying gust response factors and different wind incidences), 2) the handling of non-uniform ice loads, 3) the handling of the many phenomena that generate longitudinal loads (broken wires, slack redistribution, etc.), and 4) the possibility of interaction between flexible structures and all wires in the tension section. Therefore, for practical design reasons, approximations and assumptions have to be made. In PLS-CADD, four modeling levels are available to determine the response of the wire system to some loading criteria. These four levels are summarized in Fig. 7.1-1.

The simplest modeling level (Level 1) is based on the concept of the Ruling Span (RS) and it is sufficient in most cases. The most advanced modeling level (Level 4) is based on a full structural analysis of the entire tension section, including detailed models of all supporting structures and all cables. Because it is computer time intensive and is not justified in most situations, Level 4 should only be used in special cases where a very accurate representation of the interaction between the structures and the wires needs to be considered. You likely will never have the need for this advanced modeling capability (Level 4). Between Level 1 and Level 4, there are two intermediate modeling levels (Level 2 and Level 3). Levels 2, 3 and 4 are defined herein as Real Span (because it works with actual real lengths of wires in each span) or Finite Element (FE) modeling. The general assumptions used at these different levels are discussed in this section.

WIRE SYSTEM MODELING LEVELS

In order to use Levels 2,

FINITE

3 or 4, you must have a ^RULING

SPAN

ELEMENT

license of our SAPS

program in addition to NO INTERACTION INTERACTION BETWEEN WIRES PLS-CADD. You should ^{LEVEL 1} BETWEEN WIRES ( REQUIRES METHOD 4 STRUCTURES ) also become familiar with the material in Appendix N. Levels 2, 3 LEVEL 2 LEVEL 2 LEVEL 3 LEVEL 4

and 4 have not been ATTACHMENT SPRINGS AT STRUCTURES FULL METHOD 4 widely used due to their POINTS ATTACHMENT CONDENSED TO STRUCTURE MODELS perceived complexity. INFINITELY POINTS FLEXIBILITY MATRIX BECOME PIECES OF

AT ATTACHMENT HUGE MODEL OF

However, if you select ^STIFF

POINTS TENSION SECTION

one of these methods in ^{( DEFAULT )} PLS-CADD, the

( EFFICIENT LINEAR ( TIME CONSUMING ) APPROXIMATION )

complexity is hidden from you and you seldom

STRUCT. ATTACHMENT POINT ( INFINITELY STIFF )

realize that complex

TOP SUSP. INSUL. OR TIP OF POST INSULATOR

calculations are made in

Usefulness and practicality of method:

This is by far the most practical method and it is applicable to the overwhelming majority of line design situations. It should be used in all preliminary design situations. This is what you will use most of the time. This method works well with legislated design loads which are generally applied uniformly over a tension section. It should always be used at the preliminary design stage.

Assumptions:

1) The analysis involves a single wire (cable), in one or more spans, between dead ends, i.e. it is assumed that there is no interaction between the wire and other phases of the same electrical circuit or wires in other circuits.

2) The horizontal component of tension along the wire in all the spans of the tension section between dead ends is constant, i.e. all intermediate supports are assumed to be perfectly flexible in the longitudinal direction. This may not be very accurate in the case of rigid post insulators and short suspension insulators subjected to large vertical loads. It is usually considered sufficiently accurate in view of all the other uncertainties and approximations associated with line design. A recent IEEE report entitled Limitations of the Ruling Span Methods for Overhead Conductors at High Temperature provides some discussions on this topic (IEEE, 1997). The IEEE Guide for Determining the Effects of High Temperature Operation on Conductors (IEEE, 2002) also mentions potential problems with the ruling span assumption when calculating sags at very high temperature.

3) Based on the horizontal component of its tension, the geometry of each span is determined as discussed in Appendix J and the design loads are calculated as discussed in Section 7.3.12.

Limitations:

1) All the spans need to be subjected to the same loading, i.e. this level of modeling is not capable of analyzing situations with different ice thicknesses in various spans.

2) There is no way to study the effect of slack re-allocation due to moving a conductor attachment point or cutting/adding some wire length in a span.

3) There is no way to account for support displacements in a system where there is a fixed length of wire, for example inserting or raising a structure to fix a clearance problem without resagging the wires.

4) This level of modeling cannot be used to model an existing line where unequal tensions have been surveyed in various spans of a given tension section.

Usefulness and practicality of method:

With this method, all supports (towers, poles and frames) are assumed infinitely rigid unless you chose to insert fictitious springs between the supports and the insulators).

For conductors supported by latticed towers with suspension insulators, Level 2 should give you better sags at very high temperature than Level 1 and very good approximations of unbalanced loading situations.

Assumptions:

1) As with Level 1, the analysis involves a single wire at a time between dead ends, i.e. it is assumed that there is no interaction between different wires (other phases).

2) An accurate finite element model of the wire in all the spans between dead ends is used. This model is assumed in longitudinal equilibrium (i.e. the horizontal component of tension is assumed to be the same in all the spans) for the sagging condition, i.e. for a specified weather case and cable condition or unstressed lengths can be specified. Strain, suspension and 2parts insulators are modeled as structural elements. Attachment points at the tips of POLE

ARM

post insulators and at the structure ends of strain, suspension and 2-parts insulators

TOP VIEW

are assumed fixed in the vertical direction, ^{TOP VIEW}

PO AO

but can optionally be allowed to move in

TDTD

the transverse and longitudinal directions PD

AD LD LD

as shown in Fig. 7.1-2. The transverse and longitudinal movements of the attachment

AD

points (TD and LD in Fig. 7.1-2) depend PD on their assumed transverse and longitudinal flexibilities (or stiffnesses). ^ELEVATION With zero flexibilities, the supports are fixed. More information on this subject is _ELEVATION provided in Appendix N.

Fig. 7.1-2 Optional Springs for Level 2 Modeling

3) Once the tensions in all the spans of the tension section are determined (unlike with Level 1, you will get different tensions in different spans), the corresponding design loads are calculated using the same procedures as used with Level 1.

Limitations:

With Level 2, you can apply different loads in different spans (unbalanced ice, broken conductor, etc.), you can reallocate slack between spans and you can move attachment points. However:

1) There is still no accounting of the possible mechanical coupling between wires in different phases.

2) In the case of post insulators, it is difficult to know what value of longitudinal stiffness should be used.

Usefulness and practicality of method:

This method only works with Method 4 structures, as the flexibility matrices for all the structures are automatically re-calculated by our PLS-POLE and TOWER programs when needed. Except for some additional computer time, Level 3 has all the advantages of Level 2 without its limitations: it accounts for the interaction between the wires and relieves you from having to assume a flexibility value. However, expect approximately an order of magnitude more computer time when you use Level 3 as compared to Level 2. Level 3 is the recommended method when you have longitudinal load issues in lines supported by flexible poles and frames.

Assumptions and limitations:

If a deadend structure is being checked for loads or is part of a tension section for which tensions are calculated, its flexibility matrix, if available, is taken into account.

1) Interaction between the wires is modeled through structure flexibility matrices which are inherently linear. Thus the nonlinear effects of extremely flexible poles and frames (which may account for 10 to 20 percent of the stresses) cannot be accounted for. Guyed structures, which are also highly nonlinear, may not exhibit the correct behavior.

2) The effect on the equilibrium of the system of the wind load applied directly to the structures cannot be taken into account.

Usefulness and practicality of method:

Due to the large number of nodes and elements in the gigantic finite element model that is used internally, this method can be prohibitively computer intensive as it requires orders of magnitude more computer time and memory than Level 3. However, you may be able to work around the prohibitive time and memory demands by specifying that Level 4 only be used for guyed or flexible structures, while all latticed towers are modeled at Level 3.

Assumptions:

A Level 4 model includes few limiting assumptions unless wind is involved. The finite element model is as accurate a model of your physical line as you can hope to get. There is complete interaction between the wires through accurate behavior of the supporting structures, including their nonlinear behavior.

Limitations:

While the idea of accurately modeling an entire line segment by finite element is theoretically attractive, its practicality is limited.

1) You will rarely be able to justify the extensive time needed to run a full system model. It may take a very long time to analyze just one load case.

2) Some codes require that you apply load factors between the reactions at the ends of the spans and the supporting structures (see Section 7.3.12.3). This is an impossible situation to model with Level 4 (or Level 3 for that matter) since the structures will always respond to the unfactored loads provided by the cables to which they are connected while your code may dictate that you analyze and check the strength of these structures under factored loads.

3) While we can apply a uniform wind to an entire model (same velocity and global direction blowing on each and every span of a multi-spans model), this is not realistic. In fact we will never know what would be an appropriate wind or even a legislated wind with gust response factors to apply simultaneously to all wires and structures.

7.2.1 Wind Model

7.2.1.1 Reference Wind and Escalation with Height

A wind condition in PLS-CADD is described by a "reference wind" and various adjustments which may be made for height above the ground (even elevation above sea level according to some codes) and gustiness. The reference (or basic) wind velocity, W, is described by either keying it directly in the Weather Cases table that you reach with Criteria/ Weather, or by entering the corresponding reference pressure. It is the wind velocity at the reference height, usually taken as 10 m (33 ft) above ground. Depending on the code that governs your design, the reference wind can be a gust value (for example a 3-second gust) or a value with a longer average (1-minute average, 10-minute average, fastest mile, etc.). The reference wind velocity is related to the corresponding reference pressure by the following formula:

2

Reference pressure at reference height = Q x W (7-1)

where the Air Density Factor Q is also entered in the Weather Cases table. Common values of

temperature and elevation above sea level. While you can specify either a HEIGHT

HEIGHT

ASCE Z STAIR

reference wind or a reference Z

pressure (the other is calculated automatically with Eq. 7-1), you should

WIND WIND

be aware that in all cases, it is the displayed reference pressure which is used as the starting point of all wind

^Z REF

load calculations. ^{Z REF}

W WZ

Z WW

Many codes and criteria require that _{Fig. 7.2-1 Wind Profiles} the design wind velocity be increased with height.

Therefore, at height "z" above the ground the design wind velocity, WZ, may be higher than the reference value W. The increase may be specified by an equation (for example the profile shown on the left part of Fig. 7.2-1) or in a table (for example the stair shown on the right part of Fig. 7.2-1).

The increase of wind velocity with height, when required by a code, can be handled in two different manners in PLS-CADD.

Manual increase of wind velocity with height: If the increase is not available as part of a built-in PLS-CADD code option, you can take care of it manually and approximately by increasing the input value for the reference wind. This works well for lines with relatively uniform height, for example lines on flat terrain with similar structures and spans throughout. For example, you could use one set of criteria for short 69 KV wood pole lines with a reference wind velocity of 70 mph and another one for taller 138 KV steel pole lines with a reference wind of 90 mph.

Automatic increase of wind velocity with height: With each new version of PLS-CADD (and the associated structure programs TOWER and PLS-POLE) we are increasing the number of codes and specifications for which we are automating the increase of wind velocity with height for the purpose of calculating wire loads and wind loads on structures. For wire loads, you select the code in the Wire Wind Height Adjust column of the Weather Cases table. For wind loads on structures, you select the code in the Structure Wind Load Model column of the Structure Loads Criteria table. See “ http://www.powline.com/products/version7_loads.pdf “ for more information regarding these codes and their implementations. For the automatic options, you may have to provide some wind and terrain parameters as indicated in the Criteria/ Code Specific Wind and Terrain Parameters dialog. If you click at the bottom of the Code Specific Wind and Terrain Parameters dialog, you can visualize the different wind escalation functions and gust response factors that are used for the selected code (for example NESC 2007 in Fig. 7.2-1a).

Fig. 7.2-1a Kz and Wire Gust Response Factor for NESC 2007

The pressure due to the wind velocity at height z is calculated as:

2 2

Pressure at height z = Q x (WZ) or KZ x Q x W (7-2)

where KZ is often referred to as the velocity pressure exposure coefficient. For example, the left part of Fig. 7.2-1a shows KZ for the NESC 2002 code.

For the automatic adjustment of wind velocity with height, an effective height z has to be assumed. The assumptions described in Sections 7.2.1.1.1 to 7.2.1.1.3 are used in PLS-CADD.

7.2.1.2 Wind Load per Unit Length of Wire

The formula used in PLS-CADD for calculating the design wind load per unit length of wire, UH, is:

22

UH = WLF Q (WZ) GRFC CDC (cos[WA]) (D + 2tZ) (7-3)

where Q and WZ were defined previously and:

WLF = Weather Load Factor GRFC = Gust Response Factor for wire CDC = Drag coefficient of wire WA = incidence angle between the wind direction and a perpendicular to the span D = wire diameter TZ = ice thickness at height z

The Weather Load Factor WLF is input in the Weather Cases table and is normally equal to one.

The wire Gust Response Factor GRFC usually depends on the wire effective height, the span length and the averaging period used in the definition of the reference wind. In PLS-CADD, GRFC can be entered manually or it can be determined automatically.

Manual input of wire gust response factor: If you are not required to use a code that specifies how the gust response factor is to be calculated, you can enter its value manually in the Wire Gust Response Factor column of the Weather Cases table. If you do so, that value will be applied to the calculation of UH in all the wires in your line, regardless of their effective height and span length. For example, for a line on flat terrain with similar structures and spans throughout, you might specify a single value GRFC = 1 if your reference wind is a fastest mile or a 1-minute average wind. You might specify a smaller value, say GRFC = 0.8, if your reference wind is a 3-second gust wind. The manual option is also the one to use if your design specification calls for simple nominal values of wind pressures, say 20 psf or 800 Pa to be applied to all conductors. In these cases, the pressure is input and the gust response factor is set equal to one. Automatic calculation of wire gust response factor: If you want to have PLS-CADD automatically calculate the wire gust response factor for a supported design code, you select the code in the Wire Gust Response Factor column of the Weather Cases table. See http://www.powline.com/products/version7_loads.pdf for more information regarding these supported design codes and their implementations. For the automatic option, you may have to provide some wind and terrain parameters as indicated in the Criteria/ Code Specific Wind and Terrain Parameters menu. You can visualize the variation of the wire gust response factor by clicking at the bottom of the Code Specific Wind and Terrain Parameters dialog (for example see the right part of Fig. 7.2-1a for the NESC 2002).

The wire Drag Coefficient CDC is assumed by default to be equal to one for all wires. However, if you select one of the supported design code (in the Wire Gust Response Factor column of the Weather Cases table) the appropriate drag coefficient will be used automatically. This coefficient may be a function of conductor diameter, ice deposit or Reynold’s Number. If you are not using a supported design code and wish to use a drag coefficient different from one, you can include its effect in your input value of wire gust response factor, GRFC.

The Wind Incidence Angle WA is automatically calculated based on your wind direction selection in the Wind Direction column of the Structure Loads Criteria table.

7.2.1.2.1 Assumptions for Calculating Wind Load on all the Spans of a wire in a single tension section, UHTS , for purpose of displaying the tension section and making clearance calculations

With Level 1 modeling, when a tension section is displayed in 3-D for a particular weather case or when basic geometric clearance calculations are made, the same load per unit length UHTS is assumed on all the wires of all the spans which make up the tension section, regardless of their lengths and orientations. For the calculation of UHTS, the wind is assumed perpendicular to each span (i.e. WA = 0 or 180 degrees) and a single value of GRFC is used. GRFC is based on the effective height described in Section 7.2.1.1.2 and the ruling span of the tension section (see Section I.1 for the definition of ruling span). While there is no theoretical reason to chose the ruling span for the calculation of GRFC, since the average effect of the wind takes place over the entire length of the tension section, a conservative consistent assumption had to be made.

With Level 2, Level 3 or Level 4 modeling, a unique load per unit length, UHi, is applied to each

cable of each span. For the calculation of UHi, the wind is assumed perpendicular to the span

(i.e. WA = 0 or 180 degrees unless specified otherwise in a load case being displayed) and the gust response factor is based on the effective height described in Section 7.2.1.1.3 and the length of the span.

7.2.1.2.2 Assumptions for Calculating Wind Load on a Wire for Purpose of Determining the Contribution to Load on Supporting Structure

Consider for example the wire A-B-C-D-E-F-G shown in the plan view at the top of Fig. 7.2-2. A and G represent deadend structures. B, C, E, and F represent suspension structures or structures with flexible post insulators. When subjected to real winds (not design assumptions) each span of the wire A-B-C-D-E-F-G may be subjected to its own wind velocity, wind direction, WA*, and gust response factor, GF*. This is illustrated schematically in part (a) of Fig. 7.2-2. Obviously we will never be able to predict what combinations of velocity, direction and gust response factors is appropriate for simultaneous application to each span of a multi-span system. Therefore, some assumptions are needed for practical design. Our interest here is in calculating structure design loads at point D. This section describes the wind assumptions behind the calculations.

The transverse load at point D depends on the unit wind load UHL on the span to its left and the unit load UHR on the span to its right and on the horizontal tensions in these two spans, HL and HR.

UHL is calculated with Eq. 7-3 with the gust _{( a ) COMPLETE} ^WABC ^D response factor GFL and the wind incidence angle ^SYSTEM WAL for the left span as

G shown in part (c) of Fig. _A ^GFAB 7.2-2. In the great _WA WA _RRS majority of applications, LRS

K

your specification will _{( b )} RULING SPANS ^{H I J} require you to use a GF LRS GF _RRS wind normal to the wire,

i.e. WAL = 0 or 180 ^{LEFT RIGHT} degrees. UHR is WA _{L WA}

^{calculated with the gust} ( c ) LEFT AND RIGHT SPANS ^{D R}

response factor GFR and the wind incidence angle GF

GF_RWAR for the right span. _A ^{B C L}

^E FG Like WAL, WAR will be required by most

_{specifications to be} WIND LOADING ASSUMPTIONS WHEN " NORMAL ALL " IS NOT SELECTED

equal to 0 or 180

7.2.1.3 Wind Load on Supporting Structure

Wind loads prescribed by PLS-CADD can only be applied to supporting structures if these structures are modeled by TOWER or PLS-POLE (Method 4 structures). The following formula, which is further modified for the effect of wind direction as shown by Eqs. 7-13 and 7-14) is used to determine the design wind force, WF, applied directly to a part of a supporting structure located at height z:

2

WF = LFW WLF Q (WZ) GRFS CDS A (7-4)

where WLF, Q and WZ were defined previously (Eqs. 7-1, 7-2 and 7-3) and:

LFW = Load Factor for Wind
GRFS = Gust Response Factor for structure
CDS = Drag coefficient of structure
A = Exposed area of part of structure

An alternate form of Eq. 7-4 is: WF = LFW WLF Q (W)² KZ GRFS CDS A (7-5)

where KZ is the height adjustment factor.

The Load Factor for Wind LFW is entered in the Wire and Structure Wind Load Factor column of the Structure Loads Criteria table (Note: for users of the EN 50341-3-9: UK-NNA wind model, the number entered for LFW has a completely different purpose - it is used to enter the K-COM factor of that model).

The Height Adjustment Factor KZ is automatically accounted for in TOWER or PLS-POLE

The structure Gust Response Factor GRFS can be entered manually in PLS-CADD or it can be determined automatically in TOWER or PLS-POLE.

Manual input of structure gust response factor: If you are not required to use a code that specifies how the structure gust response factor is to be calculated, you can enter its value manually in the Structure Wind Area Factor column of the Structure Loads Criteria table.

Automatic calculation of structure gust response factor: If you want to have PLS-CADD together with TOWER or PLS-POLE automatically calculate the structure gust response factor for a supported design code, you select the code in the Structure Wind Load Model column of the Structure Loads Criteria table.

The Structure Drag Coefficient CDS is either specified or determined automatically in TOWER and PLS-POLE depending on your choice of design code in the Structure Wind Load Model column of the Structure Loads Criteria table.

The Exposed Area A of the structure is determined by TOWER or PLS-POLE. The area of the part in the TOWER or PLS-POLE model can be adjusted from PLS-CADD by a factor that you enter in the Structure Wind Area Factor column of the Structure Loads Criteria table.

When a supported design code is specified in PLS-CADD, it is important that you understand the changes that were made to the design pressure reported by PLS-CADD and passed to TOWER and PLS-POLE when we upgraded these programs to Version 7.

2

Prior to Version 7, the reported design pressure was LFW WLF Q (WZ) GRFS , where WZ was a single velocity calculated at 2/3 the height of the structure.

2

Starting with Version 7, the reported design pressure is LFW WLF Q (W) . The last portion of Equation 7-5, KZ GRFS CDS A , is automated entirely in TOWER and PLS-POLE.

7.2.2 Ice Model

7.2.2.1 Ice on Wires

Ice on wires in PLS-CADD can be specified as: 1) a combination of ice thickness and ice density, 2) a nominal load per unit length of wire, or 3) any combination of the previous two. In order to cover all the possible combinations, the vertical ice load per unit length of wire, UI, is calculated by the formula:

UI = WLF 3.1416 ( D +tZ ) tZ DENS +WICE (7-6) where:

WLF = Weather Load Factor

D = cable Diameter

TZ = ice thickness at height z

DENS = ice density

WICE = ice load per unit length

The effects of WICE and tZ are cumulative, i.e. if both are non zero, the ice load will include the sum of the two.

Some design codes require that the thickness tZ be increased with height z above the ground from the reference value “t“ (usually at 10 m - 33ft above the ground). This is handled automatically by PLS-CADD for the supported codes. The effective height is the same as that used for wind (see Sections 7.2.1.1.1 to 7.2.1.1.3). The weather load factor WLF, the reference thickness “t“, the ice density DENS and the ice load per unit length WICE are entered in the Weather Cases table.

7.2.2.2 Ice on Structures

When ice specified on wires, most design codes do not require that you apply that ice on the members of the supporting structures. However, if your design code requires that you apply ice on structure members, this is done automatically by the TOWER and PLS-POLE programs from the ice data that you specify in the Structure Ice Thickness and the Structure Ice Density columns of the Structure Loads Criteria table.

7.2.3 Load per Unit Length of Wire

The response of the wire system to wind, ice or any combination of the two t depends on the resultant weather load _D ^{UH UH} per unit length, UR (in N/m or lbs/ft). UR is the resultant of the horizontal wind load, UH in Eq. 7-3, the unit wire weight, UW, and the vertical ice load, UW UW UI in Eq. 7-6. UR is shown on the right of Fig. 7.2-3.

UI

UI UR

Under wind, the span blows out with the angle β (see Fig. J-2), the tangent ^NESC of which is UH / (UW + UI). Therefore, ^CONSTANT

^UR NESC

when a tension section is displayed for ^{a given climatic condition, the blowout} Fig. 7.2-3 Loads per Unit Length of Wire angle of each span of the tension section is the same because the wind load in each span (UHTS described in Section 7.2.1.2.1) is the same.

7.2.3.1 NESC District Case

Transmission line designers in the United States who are subjected to the National Electric Safety Code (NESC) have had to endure an archaic system of loads and strengths which has not seen much improvement over the past 50 years. Besides using arbitrary load and strength factors, Rule 250B of the NESC still prescribes a method that does not satisfy the basic principles of statics.

Under Rule 250B of the NESC 2007 (the so-called District Case): 1) the wind velocity (and pressure) is a fixed nominal value which does not depend on height and span length, 2) the wind is always applied normal to a span (i.e. there is no possibility of considering varying wind incidences -angle WA in Eq. 7-3), and 3) the resultant load per unit length of wire is increased by an arbitrary constant (the so-called "NESC Constant" or "K" constant) for the purpose of calculating wire tensions. There is no physical nor rational reason for the "K" constant to exist. The increased resultant load, URNESC , is shown on the left of Fig. 7.2-3. Therefore, any structure load based on wire tension (transverse line angle load or vertical load in case of a nonlevel span) should be based on the tension caused by URNESC. However, it has always been the intention of the NESC that the wind load on a structure only be based on the horizontal load per unit length of wire, UH, times the average length of wire in the two adjacent spans. The NESC District requirements do not satisfy statics because UH and URNESC cannot occur at the same time. There is no physical cable or general analytical 3-dimensional cable model (such as that used by our Level 2, 3 or 4 modeling or by any commercial finite element computer program) that can possibly be loaded by the NESC District load case when "K" is nonzero. Therefore, some elaborate steps had to be used to implement the NESC District Case in PLS-CADD.

7.3.1 Notes

The Criteria/ Notes menu allows you to enter up to fifty lines of notes describing the various standards, assumptions, authors, dates, etc. related to the set of criteria in a particular .cri file. A company may work with different sets of criteria at any one time, and it is extremely important to document the origin and limits of validity of a particular set of criteria.

Important Note: In any line of the Criteria Notes table you can include the complete path and file name of a set of criteria that may be used as an alternate to the current set of criteria. For example, you can have the text string “C:\PLS\Wpoles138kv.cri“ in the Criteria Notes table for a Wpoles69kv.cri file. If you do this, the alternate criteria file (or files) will be included in a backup of your model created with the File/ Backup command.

7.3.2 Weather Cases Many strength and serviceability (clearances) criteria assume that the line is subjected to a given combination of wind, ice (or snow) and temperature. Such a combination is defined herein as a "weather case". In PLS-CADD, all cable sag and tension calculations, and consequently all loads and clearance calculations, are made for designated weather cases. All

weather cases which will be used in a particular design must be described in the Weather Cases table (see Fig. 7.3-2) which you reach with Criteria/ Weather. A weather case table typically includes a group of weather cases for checking the strength of the structures, a group for checking various geometric clearances (to ground, blowout, between phases, swings, etc.), and a group for checking ground wires and conductors tensions. It also includes the weather case assumed to cause creep, the heavy load case which potentially causes permanent stretch of the various cables, and various weather cases needed for displaying the cables at various temperatures. For example, the conditions for checking structures (first four lines in Fig. 7.3-2) may include: 1) an NESC combination (see Section 7.2.3.1), 2) an extreme wind condition, 3) an extreme ice condition with some reduced wind, and 4) an extreme cold condition. There are usually a number of conditions for checking vertical, lateral and galloping clearances (lines 5 to 13 in Fig. 7.3-2). For checking the cables, the conditions may include: 1) the NESC combination, 2) no ice and no wind at an everyday temperature, etc. Therefore, for a given project, the Project.cri file may contain a substantial number of weather cases. Note: The weather cases in Fig. 7.3-2, which come from the Demo.cri file, are provided for illustration purposes only and should not be used in connection with actual projects.

Sample NESC Criteria may be downloaded from our web site at http://www.powline.com/files/criteria.html These samples are for illustration only and should not be used unless checked and modified if necessary by an engineer in responsible charge.

Data in the Weather Cases table include:

codes.

7.3.3 Code Specific Wind and Terrain Parameters

After selecting Criteria/ Code Specific Wind and Terrain Parameters, you will be taken to a series of submenus where you will have to enter code specific information regarding wind and/ or terrain parameters. Make sure that you fill out all the requested information for the design code you intend to use.

7.3.4 Conditions for Cable Creep and Permanent Stretch The mechanical cable model used by PLS-CADD for ground wires and conductors is described in detail in Section 9.1. This model allows the program to make sag and tension calculations for a cable in its "Initial", final after "Creep", and final after "Load" conditions. The cable condition

("Initial", "Creep" or "Load") is a specified item in many PLS-CADD functions. The cable is assumed to be in its "Initial" condition for the few hours which follow its installation. It is in its final after "Creep" condition after it has been assumed exposed to a particular creep weather condition for a long period of time, say 10 years. It is normally assumed that the weather case that causes creep consists of a no wind/ no ice condition at some average temperature. The average temperature of 60 deg. F is often used in North America, unless the line spends several months in very cold weather, in which case a colder value is appropriate, say 30 deg. F or less. The final after "Load" (also referred to as "final after common point") condition assumes that the cable has been permanently stretched by a specified weather condition (say the NESC District Case or any other case causing large tensions). The Weather case for final after creep or final after load conditions are picked from the list of all available weather cases in the Criteria/ Creep-Stretch menu (see Fig. 7.3-3).

7.3.5 Bimetallic Conductor Model

Because the aluminum portion of an ACSR conductor expands at a higher rate than the steel core portion at high temperature, there is a temperature beyond which the aluminum goes into compression. In the Criteria/ Bimetallic Conductor Model menu, you have the option of assuming that it is either not possible for the aluminum to go into compression (i.e. it would "bird cage" or buckle outwards) or that it can go into compression. If you assume that the aluminum can go into compression, you can enter a maximum compression stress (actually modified by the ratio of aluminum to total area of the cross section). The ridiculously large maximum stress value used as a default is equivalent to assuming that the aluminum is welded to the steel and cannot buckle outwards. See Section 9.3.2 for more details.

7.3.6 Cable Tensions

Design limits for ground wires or conductors are normally specified as maximum tensions or maximum catenary constants under specific weather conditions. These limits are specified in the

Cable Tension Criteria table (Fig. 7.34) which you open with

Criteria/ Cable Tensions. For each limit, you: 1) pick a Weather case , 2) pick a Cable condition ( "Initial", "Creep", or "Load"), 3) enter a

maximum tension as a % of Ultimate, and/ or a Maximum Tension, and/ or a Maximum Catenary constant, and 4) specify whether the limits apply to all cables or only to specific cables (Applicable cables column). For example, US practice may specify three design limits: 1) 60 % when loaded with the NESC District weather condition (Initial), 2) 35 % of ultimate or less at an everyday temperature (Initial), and 3) 25 % or less at an everyday temperature (after Creep). In addition, you may require that whenever a Drake conductor is used, its maximum tension does not exceed 15,000 lbs under some Extreme Ice case (line 4 in Fig. 7.3-4). Limiting the use of conductors by specifying a maximum catenary constant (Horizontal tension over unit weight, or H/w) is becoming the preferred scientific way to specify maximum tensions with respect to aeolian vibrations (CIGRE, 2001).

The design limits you input in the Cable Tension Criteria table are checked for an actually sagged tension section with the Sections/ Check function, as described in Section 11.2.2, or with Lines/ Reports/ Section Usage or Structure & Section Usage + Survey Point Clearances.

7.3.7 Automatic Sagging

One of the sagging methods used in PLS-CADD is to let the program sag the cables as tight as possible without violating a certain number of limits. The limits can be the same as those described in Section 7.3.6 or they can be more restrictive. The Criteria/ Automatic Sagging menu lets you define the limits for automatic sagging in the Automatic Sagging Criteria table which is similar to that shown in Fig. 7.3-4.

The design limits you input in the Automatic Sagging Criteria table are used to determine the sagging tension of a tension section when you click on the Automatic Sagging button of the Section Modify box which is available from the Sections/ Modify command. This is described in Section 10.3.2.

7.3.8 Maximum Tension

Maximum cable tensions are calculated and reported in several places by PLS-CADD. You need to tell the program whether a maximum tension is: 1) the maximum tension in the ruling span, a single fictitious span with equal end elevations equivalent to the several spans making up the tension section, or 2) the actual maximum tension in the tension section, considering both ends of each of the several spans in the tension section and changes in elevations. See Appendix I for the definition of ruling span.

7.3.9 Weight Span Model

Depending on the method used to check the strength of your structures, you may need to calculate a weight (or vertical) span. As discussed in Appendix I.3, there are different ways, from very approximate to accurate, of calculating weight spans. The Criteria/ Weight Span Model menu lets you select which calculation method you wish to use for weight spans.

7.3.10 Conditions for Checking Weight Spans of Method 1 Structures

When structures are checked by the "basic allowable wind and weight spans" method (see Method 1 in Section 8.3.1), the actual weight spans (defined in Appendix I.3) of their heaviest attached

cable are compared to corresponding allowable values for three weather conditions. These conditions normally include a "wind", a "cold", and an "iced" conditions. There must be a one-to-one correspondence between the weather conditions which were used to develop the allowable weight spans in the files of Method 1 structures and the weather conditions used by PLS-CADD to calculate actual weight spans to check these structures. This mapping is done in the Weight Span Criteria dialog box (see Fig. 7.3-5) which is reached with Criteria/ Weight Spans (Method 1).

7.3.11 Conditions for Checking Method 2 Structures

When structures are checked by the "wind and weight spans interaction diagrams" method (see Method 2 in Section 8.3.2), there is one allowable interaction diagram for each of a number of combinations of weather cases and angle ranges. The diagrams are defined in the files of Method 2 structures. There must be a one-to-one correspondence between the weather conditions which were used to develop the allowable interaction diagrams and the weather conditions used by PLS-CADD to calculate actual

wind and weight spans to check the structures with Method 2. This mapping is done in the Interaction Diagram Criteria table (see Fig. 7.3-6) which you reach with Criteria/ Interaction Diagram (Method 2). If your interaction diagrams are developed automatically by the TOWER or PLS-POLE programs for the load cases described in the Structure Loads Criteria table (see Fig. 7.3-10), then the weather cases in Fig. 7.3-6 should coincide with those in Fig. 7.3-10.

7.3.12 Load Trees for Method 3 and Method 4 Structures

When the strength of Method 3 or Method 4 structures (see Sections 8.3.3 and 8.3.4 for the definitions of Method 3 or Method 4 Structures) is checked, loading trees are established for a certain number of "load cases" and are used for the analysis of the structures. There are many assumptions which can be used to determine a loading tree. Therefore, it is important that they be clearly spelled out. This is the purpose of the following sub-sections.

7.3.12.1 Structure Axes and Orientation Relative to Line

Any structure used by PLS-CADD _LS

has its geometry described relative _LS W

+

to the structure local axes. Each

LS

structure has its local transverse ^LINE

WB

axis, TS, and its local longitudinal axis, LS, rotated 90 degrees clockwise from the transverse axis,

TS SO

when looking at the structure from _{TS SO}the top (see Fig. 7.3-7). The SO structure loading tree should have load components in the directions of Fig. 7.3-7 Structure and Wind Orientations (View from Top) the structure local axes.

When a structure is located along a line, its orientation is defined by its orientation angle, SO. SO is positive if clockwise as viewed from the top. At a line angle, SO is measured from the bisector of the line angle on the side of positive offsets, i.e. on the right when you march down the line in the direction of increasing stations. This is depicted at the center of Fig. 7.3-7 at a positive line angle (LA+) and at the right of the figure at a negative line angle (LA-). At a location where there is no line angle, SO is measured from the perpendicular to the line, as shown on the left of Fig. 7.3-7.

When a wind blows on a structure and its two adjacent spans, an option described in the next section is to describe the wind direction, WB, relative to the bisector or a global direction (see Fig. 7.3-7).

7.3.12.2 Wind Direction

There are nine wind direction options available when developing a loading tree in PLS-CADD. These options are depicted in Fig. 7.3-8 and are discussed in more detail below. The back or left span is that which corresponds to the smaller station numbers. The ahead or right span is on the other side of the structure.

With the option "NA+" (which stands for Normal All Positive), the wind blows perpendicular to the spans (left span, right span and span taps, if any). It blows on a structure located in a straight portion of the line in the direction perpendicular to the line. On a structure located at a line angle, it blows in the direction of the bisector ^{NORMAL ALL +} of the line angle. The general wind direction is always in the direction of

BISECTOR + BISECTOR

positive offsets, as shown by the

WB IS INPUT WB IS INPUT

three sketches in the upper left corner of Fig. 7.3-8. With this option, all the

NORMAL LEFT (OR RIGHT) + (OR - ) IS

wind incidence angles in Fig. 7.2-2

SAME AS BISECTOR + (OR -) WHERE ANGLE WB IS CALCULATED SO THAT WIND

(WAL, WAR, WALRS, WARRS, etc.) are

_{set to zero. At a line angle, this} NORMAL ALL -IS PERPENDICULAR TO LEFT (OR RIGHT) SPAN

^{situation cannot describe a real wind,} Fig. 7.3-8 Available Wind Direction Options (View from Top)

but it is often used as a conservative
assumption, especially when nominal wind pressures are specified.

The "NA-" (which stands for Normal All Negative) option is identical to the "NA+" option, except
that the wind blows in the opposite direction of that of "NA+", as depicted by the three sketches
in the lower left of Fig. 7.3-8.

With the option "BI+" (which stands for BIsector Positive), the wind blows in the general
direction of positive offsets and in the direction defined by the wind angle, WB, which is
measured from the perpendicular to the line or the bisector of the line angle on the side of
positive offsets. The situation is depicted by the three sketches in the center of Fig. 7.3-8. The
value of WB should be between -90 and +90 degrees. With this option, the wind incidence

angles for the left and right spans (WAL and WAR in Fig. 7.2-2) are calculated internally so that the wind velocity vectors on the spans and on the structure are all parallel to each other.

With the option "BI-", the wind blows in the general direction of negative offsets and in the direction opposite to that defined by the angle WB. The situation is depicted by the three sketches in the top right portion of Fig. 7.3-8. As with the "BI+" option, the value of WB should still be between -90 and +90 degrees.

The option "NL+" (which stands for Normal Left Plus) is similar to "BI+", except that there is no need to input the value of WB. WB is calculated internally so that the wind is perpendicular to the left span.

The option "NL-" is similar to "BI-". WB is calculated internally so that the wind is perpendicular to the left span.

The option "NR+" is similar to "BI+". WB is calculated internally so that the wind is perpendicular to the right span.

The option "NR-" is similar to "BI-". WB is calculated internally so that the wind is perpendicular to the right span.

The option "GLB" lets you blow the wind in a global direction (relative to north).

Note: The options NL+, NL-, NR+ and NR- should not be used with PLS-CADD/ LITE models as such models do not include the concept of left (back) and right (ahead) spans.

To make sure that unsymmetrical structures are checked for wind in both the positive and negative directions, it is recommended that each load situation which includes some wind be described by two load cases: one with the wind in the positive direction and one with the wind in the negative direction. Therefore, in general, wind load cases should appear in pairs, for example one load case with "NA+" and the associated load case with "NA-". The program will issue a warning if it detects unpaired wind load cases.

7.3.12.3 Reactions at Ends of Span (in span coordinate system)

When determining a loading tree, PLS-CADD computes first the reactions at the ends of all cables attached to the structure. These normally include the cables in the left and the right spans, but they may also include ^LA cables in taps as shown in Fig. 7.3-9. In Fig. 7.3-9, the arrows at the ends of the lines representing the spans are the reactions at the ends of these spans, while the opposite arrows on the small square at the center of the figure represent the equal and opposites actions (loads) on the

^structure. Fig. 7.3-9 Loads in Span Coordinate System

The reactions at the right end of one cable in the left span are: 1) a vertical force VL, 2) a transverse horizontal force TL perpendicular to the span and opposite to the direction of the wind, and 3) a longitudinal force LL equal to the horizontal component of cable tension (see Fig. 7.3-9).

The reactions at the left end of one cable in the right span are: 1) a vertical force VR, 2) a transverse horizontal force TR perpendicular to the span and opposite to the direction of the wind, and 3) a longitudinal force LR equal to the horizontal component of tension in the cable.

Similar reactions can be defined at the end of taps.

The sign conventions regarding vertical and transverse forces in the span coordinate system are as follows: 1) vertical forces are positive if they pull down on the structure, and 2) transverse forces are positive if their actions on the structure have positive projections in the positive bisector direction (see Fig. 7.3-9), or the positive offset direction if there is no line angle. Longitudinal forces in the span coordinate system are always positive.

The procedure used in PLS-CADD for calculating the reactions at the ends of a cable is a three step process. First, the horizontal tension, H, and the unit wind load on the cable, UH, are determined based on the gust response factors and wind direction assumptions described in Section 7.2.1.2.2. From UH, the resultant load per unit length of cable, UR, is determined as described in Section 7.2.3. Then, H and UR are used in the equations in Section J.1.1. Finally, the span end reactions are obtained with Eqs. J-11 to J-13 in Section J.1.2. With unequal end elevations, the procedure yields end span forces which can be slightly different from what would be obtained by the simpler concepts of wind and weight spans.

Factored reactions at the ends of bundle in span

Sometimes, load (or safety) factors are applied to the V, T and L span reactions. The span may also consist of a bundle of cables instead of a single cable. Therefore, factored bundle span reactions are determined as follows for the left and right spans, respectively:

VL* = LFV { NCL VL} (7-7) TL* = LFW { NCL TL} (7-8) LL* = LFT { NCL LL } (7-9)

VR* = LFV { NCR VR } (7-10) TR* = LFW { NCR TR } (7-11) LR* = LFT { NCR LR } (7-12)

Where:

LFV = Load factor for vertical load
LFW = Load factor for wind
LFT = Load factor for tension
NCL = Number of subconductors in left bundle
NCR = Number of subconductors in right bundle

Similar equations are used for taps.

For example, recent editions of the NESC have specified LFV = 1.5, LFW = 2.5 and LFT = 1.65 for District Loads applied to steel structures.

7.3.12.4 Design Loads at Structure Attachment Points

The factored reactions at the ends of all the bundles that meet at a structure or insulator attachment point are combined with the weights (if any) of the insulator, WINS, and counterweight, WCW, to form the design loads at the structure attachment points. The design loads constitute the structure loading tree. These design loads are defined by their components in the directions of the local structure axes. The structure transverse and longitudinal axes, TS and LS, are shown in Fig. 7.3-7.

Loads from Left Span

The transverse and longitudinal design loads contributed by the left span are the projections of the span loads TL* and LL* in Eqs. 7-8 and 7-9 in the directions of the structure axes TS and LS shown in Fig. 7.3-7. The vertical design loads are the sum of VL* in Eq. 7-7 plus the weights of the attached insulators and counterweights times the Load Factor for Structure weight, LFS.

Loads from Right Span

The transverse and longitudinal design loads contributed by the right span are the projections of the span loads TR* and LR* in Eqs. 7-11 and 7-12 in the directions of the structure axes TS and LS shown in Fig. 7.3-7. The vertical design loads are the sum of VR* in Eq. 7-10 plus the weights of the attached insulators and counterweights times the Load Factor for Structure weight, LFS.

Loads from Taps

The loads from taps which are not part of the left and right spans are calculated in the same manner as those in these left and right spans. The end of tap spans are modeled by structures which are offset from the main alignment or are on a branch, tap or parallel alignment.

You can use Structures/ Loads/ Report to generate the complete structure loading tree report as well as the factored span reactions of Eqs. 7-7 to 7-12.

NESC District Load Case

The oddity of the NESC District Load Case was first described in Section 7.2.3.1.

The handling of "K" was never a problem when used in conjunction with the traditional Wind & Weight Spans method for the calculation of structure loads. Such calculations were usually made as follows. First, the cable mechanical tension, H, was determined, either manually or using a sag-tension program. H was then used to cut a template with which the cable catenary curves were drawn in the two spans adjacent to the structure. These curves were drawn as if they are in a vertical plane, even though they can only exist in the blown out plane defined by the direction of URNESC. The horizontal distance between the low points in the adjacent catenaries were generally used as the Weight Span. The vertical load was then calculated as the product of UV times the Weight Span. Because the actual location of the low points on blown out cables with unequal end elevations can differ from that determined with the vertical template, that traditional calculation of vertical load could lead to substantial errors. The wind component of the transverse load was calculated as the product of UH times the Wind Span. Finally, the tension component of the transverse load was calculated on angle structures by projecting the cable mechanical tensions in the structure transverse direction. The decomposition of the transverse load into wind and tension components allowed the NESC to specify different load factors for each.

The traditional Wind & Weight Span method works well for developing loads for a new family of structures designed to support pre-determined combinations of wind and weight spans. In such cases, you should use PLS-CADD/ LITE with the Wind + Weight Spans Design Mode option, as described in Section 15. With that option, PLS-CADD will give results identical to the traditional method, regardless of whether a nonzero "K Constant" is used.

The traditional method does not work well for the determination of actual loads on structures already spotted on an uneven terrain, unless the effect of span blowout on weight span is taken into account. This is one of the reasons why the models described in Appendix J have been adopted. However, because PLS-CADD uses URNESC and its direction to determine the end cable forces, some adjustment is needed. Without the adjustment, it would be as though UH and UV were scaled up to match URNESC and the transverse and vertical loads would be larger with "K" than without it, a result which we believe is not the intention of the NESC. The adjustment we have implemented in PLS-CADD in the case of a nonzero "K" it to scale down VL, VR, TL and TR in Section 7.3.12.3 by the ratio UR / URNESC.

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008

7.3.12.5 Design Pressures on Structure Faces

A complete load tree for a structure includes not only the design loads at the structure attachment points but also the design pressures to be applied to the body of the structure itself in its transverse and longitudinal directions. The design pressures depend on the relative orientation of the wind and the structure.

Starting with Version 7, the following formulae are used by PLS-CADD to compute the reference Structure design PRessures, SPRT and SPRL to be used in the transverse and longitudinal directions of the structure, respectively:

2

SPRT = LFW WLF Q (W)cos[WB - SO] (7-13)
2

SPRL = LFW WLF Q (W) sin[WB - SO] (7-14)

where (see Eq. 7-5):

LFW = Load Factor for Wind (input in Structure Loads Criteria table)
WLF = Weather load factor (input in Weather Cases table)
Q = Air density factor (input in Weather Cases table)
W = Reference wind velocity (input in Weather Cases table)
WB = Wind direction angle as defined in Fig. 7.3-7
SO = Structure Orientation angle as defined in Fig. 7.3-7

The structure pressures SPRT and SPRL are available in the loads tree report which you generate with Structures/ Loads/ Report.

When used in conjunction with TOWER and PLS-POLE, PLS-CADD transmits these pressures to these programs through their load cases files (“*.lca“ or “*.lic“ files). These pressure will find their way in the transverse and longitudinal pressures columns of the load case files. Then TOWER or PLS-POLE will automatically adjust them by the factors KZ , GRFS and CDS described in Equation 7-5 as required by a particular design code, and multiply them by the appropriate exposed area A to get the final structure wind forces.

7.3.12.6 Load and Strength Factors

In order to provide a flexible implementation of Load & Resistance Factored Design (LRFD), or the similar system of "overload capacity" factors required by the NESC, when PLS-CADD is used in combination with our structure programs PLS-POLE and TOWER, it is necessary to coordinate the values of the Load Factors (developed in PLS-CADD) with those of the Strength Factors ultimately used in the structure programs.

The typical LRFD equation for one load case can be written as:

Load Factor x Nominal Design Loads < Strength Factor x Nominal Design Strength (7-15)

In Eq. 7-15, the strength side can have a multitude of combinations. For example, for a wood frame structure with a steel cross arm, a strength factor of 0.65 may be assigned to the wood poles and a strength factor of 1.0 may be assigned to the cross arm.

Load Factors available in PLS-CADD are:

LFV = Load Factor for Vertical load (see Eqs. 7-7 and 7-10)

LFW = Load Factor for Wind (see Eqs. 7-8 and 7-11)

LFT = Load Factor for Tension (see Eqs. 7-9 and 7-12)

LFS = Load Factor for Structure weight

Nominal Design Loads in PLS-CADD are all the loads shown in the previous sections prior to the application of the load factors.

Ten Strength Factors can be passed to the structure programs by PLS-CADD for each factored load case. These factors are:

Strength factor for steel poles, tubular arms or towers:

Strength factor applied by PLS-POLE to the calculated strength of all tubular steel poles, tubular steel arms and tubular steel cross arms in the model and by TOWER to the strength of steel angles and bolted connections. It is not applied to steel cables and guys.

Strength factor for wood poles:

Strength factor applied by PLS-POLE to the calculated strength of all wood poles.

S.F.

for concrete poles - Ultimate:

S.F.

for concrete poles - First crack:

Strength factor applied by PLS-POLE to the ultimate bending capacity of all concrete pole segments.

Strength factor applied by PLS-POLE to the moment causing the first crack in a concrete pole segment.

S.F. for concrete poles - Zero tension.:

Strength factor applied by PLS-POLE to the moment causing no tension in the concrete of a concrete pole segment. It is the moment that would cause an existing concrete crack to re-open.

S.F. for guys and cables:

Strength factor applied by both PLS-POLE and TOWER to the tension capacity of all cables and guys

S.F. for non-tubular arms:

Strength factor applied by PLS-POLE to the strength of all arms and cross arms which are not made of tubular steel

S.F. for Braces:

Strength factor applied by PLS-POLE to the strength of all braces

S.F. for Insulators:

Strength factor applied by PLS-POLE and TOWER to the strength of all insulators

S.F. for Foundations:

Strength factor applied by PLS-POLE and TOWER to the strength of all foundations

A strength factor entered as zero in Eq. 7-15 indicates that the particular factored load case should not be used for checking the components associated with the particular strength factor. For example, in order to implement the alternate method for wood of the 2002 version of the NESC District Case for a wood frame with a steel cross arm (not tubular steel), two factored combinations would be used:

Load case # 1 (for checking the wood poles only):

LFV = 2.2, LFW = 4, LFT= 2,LFS = 2.2
Strength factor for non-tubular arms = 0
Strength factor for wood poles = 1

Load case # 2 (for checking steel cross arm only):
LFV = 1.5, LFW = 2.5, LFT = 1.65, LFS = 1.5

Strength factor for non-tubular arms = 1
Strength factor for wood poles = 0

Factored loads developed by PLS-CADD can be exported as standard load files (in the ".lca" and ".lic" standard formats discussed in the Structure Program manuals) using the Structures/ Loads/ Write LCA (or LIC) File command. These files include the strength factor information for each load case. You may also write multiple LCA files for use in the PLS structure programs for a range of structures in PLS-CADD by going to Lines/Reports/Structure Loads Report and checking the box at the bottom of the dialog box.

The Load Factors and Strength Factors are only used for the check of Method 4 structures by PLS-POLE or TOWER. They are not used and are not necessary when you check the strength of Method 1 (Basic allowable spans) or Method 2 (Interaction diagrams between allowable spans) structures. The Load Factors information is used, but the Strength Factors information is not used and is not necessary when you check the strength of Method 3 (Critical components) structures.

7.3.12.7 Unbalanced Loading

PLS-CADD has the ability to develop loading trees for situations where the loads are not the same on either side of a structure. This situation is defined herein as "unbalanced loading". There are some commands that allow you to modify the loads in any one of the "back" spans or the "ahead" spans. Therefore, it is essential that you understand what are back and ahead spans. Fig. 7.3-9a will help clarify the definitions.

The sketches in Fig. 7.3-9a are top views of ² a main structure S

TOP VIEWS

(represented by a square) and the spans

B

radiating from it.

A

Structures at the ends of the radiating spans

A B

(end span structures) are depicted by small circles.

The left of Fig. 7.3-9a represents structures STRUCTURES IN FULL PLS -CADD STRUCTURES IN PLS - CADD / LITE

^{and spans that are part} A -S -B IS ALIGNMENT A -S -B IS FICTITIOUS ALIGNMENT of a full PLS-CADD IN LONGITUDINAL DIR. OF STRUCTURE model. The structures are located by their

SPAN # -S IS A BACK SPAN FOR STRUCT. S IF ITS PROJECTION ON ALIGNMENT

projections (stations) on

IS TO THE LEFT OF S - OTHERWISE IT IS AN AHEAD SPAN

the alignment and their offset from that Fig. 7.3-9a Definitions of Back and Ahead Spans alignment. In this example, the alignment A-S-B has a line angle at S. Back spans for Structure S (1-S, 2-S and 5S) are those for which the stations of the end span structures are smaller than the station of S. Ahead spans (S-3 and S-4) are the others.

The right of Fig. 7.3-9a represents structures and spans that are part of a PLS-CADD/ LITE model (PLS-CADD/ LITE is described in Section 15). In such a model the end span structures are located by their azimuth (relative to the transverse axis of the main structure S) and span lengths. Therefore, in this case, there is no defined alignment. However, in order to use the same definitions of back and ahead spans as used for a structure in a full PLS-CADD model, we define a fictitious straight line alignment that is perpendicular to the transverse axis of the structure.

To simulate unbalanced loading, PLS-CADD allows you to modify the amount of wire loading on (or from) up to ten (10) individual wires attached to a structure. This is done by letting you modify, for each load case, the original load on the wire or the load transmitted by the wire to the structure. For each modified wire load (there are 10 possible such modifications labeled #1 to #10 at the top of the rightmost columns of the Structure Loads Criteria table), you will need to enter three pieces of data: 1) which wire (or wires) is to be acted upon in the “Wire (s) - Set - Phase - Span“ column , 2) what is being modified in the “Command“ columns, and 3) the magnitude or extent of the modification in the “Value -% - # Subconductors“ column.

What you can modify in the “Command“ columns is described in Sections 7.3.12.7.1 to

7.3.12.7.7 below.

7.3.12.7.1 Adjust Percent of Horizontal Tension

If you specify “Percent Horizontal Tension“ for a particular span, the vertical, transverse and longitudinal reactions at the end of the span (shown in Fig. 7.3-9 and calculated as described in Section J.1.2) will be based on a reduced horizontal tension H loads which is the original unreduced tension adjusted by the percent value you enter in the adjacent “Value - % -# Subconductors“. This option is only available with ruling span modeling (Level 1).

For example, you could model a broken conductor situation where you expect the Residual Static Load to be 70% of the original tension by specifying a 0 % of tension in the back span and a 70% of tension in the ahead span.

7.3.12.7.2 Specify Number of Broken Subconductors

If you specify “# Broken Subconductors“, you will have to enter the number of broken subconductors in the adjacent “Value - % - # Subconductors“ column. If the affected span has only one wire, you can only enter one broken subconductor. If the affected span has several subconductors, you can enter one or more broken subconductors.

With Level 1 load modeling, this option simply remove the load transmitted by the broken cable to the structure but does not change the loads from the still intact cables in the span (bundle) or from the cables on the other side of the structure. With Level 2, 3 or 4 modeling, the broken cable (s) is physically removed from the model, but the finite element analysis determines new tensions in the system after the removal.

This option can be used with Level 1 modeling to determine the loads on one side only of a rigid dead end structure: one load case where you break all the subconductors in the back spans and another one where you break all the subconductors in the ahead spans.

This option can also be used with Levels 2, 3 or 4 modeling to determine the load from a broken conductor next to a suspension insulator. The analysis would account for the reduction in tension due to the longitudinal insulator swing.

7.3.12.7.3 Add a Concentrated Vertical Load

If you specify “Add Vertical Load“, you will have to enter the value of that load in the adjacent “Value - % -# Subconductors“ column. This load will be added to the vertical load coming from the selected span. It is multiplied by the Load Factor for Vertical load (see Section 7.3.12.6) before being added. The transverse and longitudinal components are not affected. This, and the following two options, can be used for all wire modeling levels (Levels 1 to 4).

7.3.12.7.4 Add a Concentrated Transverse Load

If you specify “Add Transverse Load“, you will have to enter the value of that load in the adjacent “Value - % -# Subconductors“ column. This load will be added to the transverse load coming from the selected span (i.e. it is perpendicular to the span). It is multiplied by the Load Factor for Wind before being added. The vertical and longitudinal components are not affected.

7.3.12.7.5 Add a Concentrated Longitudinal Load

If you specify “Add Longitudinal Load“, you will have to enter the value of that load in the adjacent “Value - % - # Subconductors“ column. This load will be added to the longitudinal load coming from the selected span, i.e. it is in the direction of the span. It is multiplied by the Load Factor for Tension before being added. The vertical and transverse components are not affected.

7.3.12.7.6 Adjust Ice Thickness

If you specify “% Ice Thickness“, the ice thickness on the specified wire (s) will be adjusted by the % amount that you enter in the adjacent “Value - % - # Subconductors“ column. This option can only be used with Levels 2, 3 or 4 wire modeling. With this method, longitudinal insulator swings at all suspension structures and longitudinal deflections at all attachment points with nonzero longitudinal stiffness are accounted for. This option should not be used with Level 1 modeling because that modeling is not capable of handling longitudinal insulator swings. If you use this option with Level 1, you will get very conservative longitudinal loads.

7.3.12.7.7 Adjust Vertical (or Transverse or Longitudinal) Load

If you specify “Percent Vertical (or Transverse or Longitudinal) Load“ for a particular span, the vertical (or transverse or longitudinal) reactions at the end of the selected span (see Fig. 7.3-9) will be adjusted by the percentage that you enter in the adjacent “Value - % - # Subconductors“ column before it becomes a load on the supporting structure.

While "unbalanced" loading as described above is available, there is no easy way in PLS-CADD to generate loads from "pattern" loading, for example ice load on every other span. For “pattern” loading, you can selectively load individual spans with ice as discussed in Section N.5.

7.3.12.8 Structure Loads Criteria Table

All data needed to determine a structure load tree are included in the

Structures Loads Criteria table (see Figs. 7.3-10a, 7.310b and 7.3-10c) which you open with

Criteria/ Structure Loads (Meth. 3,4)

There is one line in the table for each load case. The loads data are:

Description:	Self explanatory
Weather case:	Weather case from list of available combinations of wind, ice and temperature (from data in Weather Cases table of Fig. 7.3-2)
Cable condition:	State of cable when calculating load. Initial RS, after Creep RS or after heavy Load RS if the calculations should be made with the ruling span method (Level 1). Initial FE, after Creep FE or after heavy Load FE if the calculations should be made with a finite element analysis (Levels 2, 3 or 4). Initial RS is the most common choice.
Wind direction:	Pick list from eight available directions described in Section 7.3.12.2

Bisector wind direction, WB: Wind direction defined in Figs. 7.3-7 and 7.3-8. Only needed if Wind direction is selected as "BI+" or "BI-"

Wire Vertical load factor, LFV; Wire Wind load factor, LFW; Wire Tension load factor, LFT; Structure weight load factor, LFS:

Load factors used in various equations of Sections 7.3.12.3, 7.3.12.4 and 7.3.12.5. The wire loads listed in the report that you obtain with Structures/ Loads/ Report include these load factors.

Structure Wind Area Factor: This factor is not used by PLS-CADD but is passed to TOWER or PLS-POLE when needed to adjust the exposed area of the model. When you import older PLSCADD models (pre Version 7), this factor is used to display the manually entered structure gust response factor. For users of the “EN 50341-3-9: 2003 UK-NNA“ wind model, this factor is used to enter the K-COM factor.

Structure Wind Load Model: Name of procedure or design code for the calculation of wind load on exposed area of a structure. This information is not used by PLS-CADD but is passed to TOWER or PLS-POLE when needed by these structure programs to determine the factors KZ , GRFS and CDS described in Section 7.2.1.3. For more information regarding supported design codes go to:

http://www.powline.com/products/version7_loads.pdf

Structure Ice Thickness and Structure Ice Density:

Uniform ice thickness deposited on structure members of TOWER and PLS-POLE models, and corresponding ice density. Very few design codes require that ice be applied to structure members.

Strength factors:

Ten strength factors to be used as described in Section

7.3.12.6. These factors are not used by PLS-CADD but are passed to TOWER and PLS-POLE.

The rest of the data (see Fig. 7.3-10c) apply to unbalanced loading as described in Section

7.3.12.7.

Structures Types on Which to Apply:

You can select to apply the adjustments described in the following columns to All structures, or to Deadend structures only or to Tangent structures only (or to structures modeled with TOWER only or with PLSPOLE only). Deadend structures are assumed to be those which have at least one attachment set dead-ended. Default is All.

Adjust cable loads:

You select N (for No) if you do not want to apply any load adjustment to the wire loads. This is the default which will grey out all the following columns which need not be considered.

You select Y (for Yes) if you want to make any adjustment to the loads from the intact wires. In this case, you will be able to access up to ten sets of three columns in which you specify the adjustments described in Section 7.3.12.7. In one or more set of three columns you enter the following data:

Wire (s), Set, Phase, Span:

Select “Back Spans“ to apply the adjustment to all the wires in the back spans (see definition of back spans in Fig. 7.3-9a of Section 7.3.12.7). Select “Ahead Spans“ to apply the adjustment to all the wires in the ahead spans. Select "i : j : Back" or "i : j : Ahead" to apply the adjustment only to the j-th wire of the i-th set in the back or ahead span. You can apply the adjustment to any of 3 phases of 60 different sets.

Command:

Select “% Horizontal Tension, # Broken Subconductors, Add Vertical Load, Add Transverse Load, Add Longitudinal Load, % Ice Thickness, % Vertical Load, % Transverse Load or % Longitudinal Load“ to implement one of the adjustment methods described in Sections

7.3.12.7.1 to 7.3.12.7.7.

Value, %, or # subconductors:

This is the value of the additional load you specify (see Sections 7.3.12.7.3 to 7.3.12.7.5). Or it is the percent adjustment you want to apply to a particular quantity (see Sections 7.3.12.7.1,

7.3.12.7.6 and 7.3.12.7.7): % Tension only available with Level 1 and % Ice Thickness only available with Level 2, 3 or 4. Or it is the number of broken subconductors (see Section 7.3.12.72).

7.3.13 Conditions for Checking Survey Points Clearances

Clearances from the centerline, side profiles or from survey points can be checked graphically and this is the most straightforward method. The phases are displayed for the desired weather cases and cable conditions (see Section 5.4.6.3) and clearance lines are displayed for the desired voltage (see Section 6.10.2). Any violation can be observed visually.

However, there is a more thorough method for checking survey point clearances as described in Section 11.2.3.1. The checks are made when you use either the Terrain/ Clearance function or ask for a complete report with Lines/ Reports/ Survey Point Clearances. The program determines the positions of the wires in relation to the survey points for the combinations of Weather Cases and Cable Conditions specified in the Criteria/ Survey Point Clearances dialog box shown in Fig. 7.3-11, and then reports any clearance violations. Clearance violations are based on wire voltages and clearance requirements established in the Feature Codes table (see Section 6.1.1).

For weather cases that include wind, PLS-CADD will always check the clearances for the designated wind velocity blowing first from the left and then from the right. However, it can also check the clearances for all the positions of a wire at it swings between the blown-out positions due to the left and right winds. This option can be used in the rare cases where a lesser wind than the one specified in your clearance criteria is critical.

Meeting survey point clearances is one of the constraints used in the automatic optimum spotting process described in Section 14.

The combinations of weather cases and cable conditions entered in the Survey Point Clearance Criteria dialog of Fig. 7.3.11 are also used by the Clearances to TIN and Isoclearance Lines functions described in Section 11.2.3.4 and by the Danger Tree Locator function described in Section 11.2.9.

7.3.14 Conditions for Checking Clearances between Cables

The two combinations of

3

weather and cable conditions ¹ specified in the Criteria/ Phase 3

Clearances menu are used as default values for the calculations of minimum

1

1distances between the cables of any two sets within a

2

selected span or within two crossing spans. For example, Fig. 7.3-12 shows two cable

MARKERS

sets, each with three phases, within crossing spans. The selection of the two sets, 2 weather case and cable condition is done with

CABLE CONDITION K

^Sections/ Fig. 7.3-12 Minimum Distances Between Cables

Clearances/Between
Sections. Minimum distances are reported and their locations indicated by markers as shown in
Fig. 7.3-12. They are also compared to minimum allowable values entered in the Sections/
Clearances menu.

It is permissible to select Sets A and B in Fig. 7.3-12 as the same set. This can be used to
calculate clearances between cables of the same set for two separate weather conditions, for
example one phase loaded with ice and that immediately below unloaded.

7.3.15 Conditions for Drawing Galloping Ellipses

PLS-CADD can draw single loop and double loop galloping ellipses that simulate the empirical envelopes of a galloping conductor according to the REA Bulletin 1724E-200 (REA, 1992) or Cigre Report 322 (Cigre Task Force B2.11.06, June 2007). It can also determine the closest distances between these ellipses, whether they are crossing each other and if so what percentage of their area overlaps. The parameters which determine the location and geometry of an ellipse (see Fig. 7.313) are: the "SAG" length, the span swing angle "SSW", the "B" distance, the ellipse "MAJOR" and "MINOR" axes, the ellipse swing inclination "ESW" from vertical and the (sub)conductor diameter

"DIA".

For single loop ellipses, PLS-CADD uses the following REA Bulletin equations to determine the numerical values of the ellipse parameters (lengths are in meters):

PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008 125 ESW = SSW / 2 (7-22) MAJOR = 1.25 X SAG + 0.3048 (7-23) MINOR = 0.4 X MAJOR (7-24) B = 0.25 X SAG (7-25)

For double loop ellipses, the following equations are used:

2

MAJOR = SQRT[ {3 A / 8} {L + 8 SAG/ (3L) - 2A} ]+ 0.3048 (7-26) MINOR = 1.104 X SQRT[ MAJOR - 0.3048 ] (7-27) B = 0.2 X MAJOR (7-28) where 22

L =Span length and A= SQRT [ (L / 2) + SAG ]

With the Cigre method for a single (unbundled) wire the following equations are used:

MAJOR = DIA X 80 X ln(8 SAG / (50 DIA)) (7-29) MINOR = 0.4 X MAJOR (7-30) B = 0.3 X MAJOR (7-31) ESW = 0 (7-32)

With the Cigre method for bundled wires the following equations are used:

MAJOR = DIA X 170 X ln(8 SAG / (500 DIA)) (7-33) MINOR = 0.4 X MAJOR (7-34) B = 0.3 X MAJOR (7-35) ESW = 0 (7-36)

For all methods you may optionally input a Galloping Safety Factor (GSF) in Criteria/ Galloping which multiplies MAJOR in Eq. 7-22 through 7-36. Finally, Criteria/ Galloping also allows you to set ESW to zero (override Eq. 7-22)

Drawing galloping ellipses and determining the distances between them is done with the Sections/Clearances/Galloping Ellipses command. The calculations are done for the combination of weather cases and cable conditions specified in the Criteria/ Galloping menu. According to the REA Bulletin, one combination of 1.27 cm ice (0.5 in.), 95.8 Pa (2 psf) wind and 0 deg. C (32 deg. F) temperature has to be specified for the calculation of the position of the insulator and the span swing angle SSW. Another combination of 1.27 cm ice (0.5 in.), no wind and 0 deg. C (32 deg. F) is specified for the span "SAG".

7.3.16 Conditions for Checking Suspension Insulator Swings and Load Inclinations on 2-parts Insulators

Lateral swings in suspension insulators (SA in Fig. 7.3-14) or load inclinations (LA in Fig. 7.3-15) at the common point of 2-parts insulators can be calculated for up to four separate combinations of weather and cable conditions. This is done as part of the Structures/ Check function. The function also compares the results with allowable values which are described in the corresponding structure file. Insulator swing limits or load angle limits are parts of the constraints used in the automatic optimum spotting process described in Section 14.

For each circuit supported by a suspension insulator, the structure file includes allowable swings for four conditions. For 2-parts insulators, the file includes allowable load angles. There is a Fig. 7.3-14 Insulator Swing minimum and a maximum allowable swing or load angle for each condition. The swing angle, SA (or the load angle LA), is measured from vertical and is positive if the insulator (load) moves in the transverse direction of the structure as shown in Figs. 7.3-14 and 7.3-15. The allowable values are algebraic and should follow the sign convention (see Figs. 7.3-14, 7.3-15 and 7.3-16). Note that maximum swing is defined as that which translates the bottom point of the insulator the farthest in the transverse direction of the structure. You need to specify the conditions for which the allowable swings or load angles apply. One possible set up is:

Condition 1: Everyday condition with no wind and average temperature. This is a condition under which the line will spend most of its life, and therefore it is the condition most likely to occur when a serious voltage surge occurs. To avoid flashover under that condition, one may specify the most restrictive values of allowable swing.

Condition 2: Cold condition with average wind. Because of the cold temperature, this is a condition under which the vertical load may be too small to prevent a significant insulator swing, even under average wind. Because the probability of occurence of a serious voltage surge under the cold condition is not as high as at any random time, one may specify less restrictive values of allowable swings than under Condition 1.

Condition 3: High wind condition. High winds are rare events. The combined probability of their occurrence together with a voltage surge is even smaller, thus it may be appropriate to relax the swing requirements even more.

Condition 4: Everyday or colder condition with average wind under Final tension such as that proposed in the REA Manual 1724e-200 for medium and large angle structures. This value may be slightly less restrictive than Condition 1.

The Criteria/ Insulator Swing menu is used to describe the combinations of weather and cable conditions that correspond to the four conditions which were used to develop the allowable values in the structure model.

C DOWN A

The procedure used by the Structures/ Check function to compare an actual swing (or inclination angle) to the corresponding allowable value systematically blows the wind perpendicularly to each of the two spans adjacent to the structure and in both directions, i.e. the swing calculation is done twice for each specified weather condition. From these calculations, the largest and smallest values are kept for comparisons with the maximum and minimum allowable values.

The actual swing angle SA for a suspension insulator (see Fig. 7.3-14) is determined by the following equation:

SA = TANGENT^-1 [ ( T+ TINS / 2 ) / (V + VCW + VINS / 2 ) ] (7-379)

where T = transverse load from conductor, V = vertical load from conductor, VCW = weight of optional counterweight, VINS = weight of insulator and TINS = wind load on insulator calculated as the product of the pressure at the height of the insulator (pressure from Eq. 7-2) times the insulator wind area (see Section F.1.1.3). For swing calculations, all load factors in Eqs. 7-7 to 7-9 are equal to one.

For 2-parts insulators, the load angle (se Fig. 7.3-14) is determined by the following equation:

LA = TANGENT^-1 [ ( T + TINS ) / (V +VCW + VINS ) ] (7-38) where VINS = total weight of both sides and TINS = total wind load on both sides of 2-parts insulator (see Eq. 7-37 for more detail).

Note the number of allowable swing conditions associated with a structure file must match the number defined in the Insulator Swing Criteria or an error message will appear when checking the strength of the structure.

7.3.16.1 Structures with Suspension Insulators at Line Angles

There are two methods for handling unsymmetrical structures with suspension insulators at line angles. With the first method, you need to have two separate structure models (i.e. you need two separate structure files): a right turn structure for use at positive line angles and a left turn structure for use at negative line angles. An example of such two structures is shown in the left part of Fig. 7.3-16. With the second method, you only need to model the right turn (or left turn) structure (i.e. you only need one structure file). You can use that single model (the right turn

structure) without rotation at positive line angles and rotate ₁

2 3

it 180 degrees about its vertical axis at negative line angles. Structure orientation

+

1

about its vertical axis is

^SA MAX

defined in Fig. 7.3-7.

T

+

_{We highly recommend the} SA _MIN FRAME AT POSITIVE LINE ANGLE

+ 2

second method even though it

3

may require that you manually ¹

SA

MAX MIN

transpose some phases. The

T

differences between the two

-

methods are further discussed

SA MIN SYMMETRICAL STRUCTURE

below.

T -

FRAME AT NEGATIVE LINE ANGLE SA MAX

Fig. 7.3-16 Unsymmetrical Frames

Using two different unsymmetrical structures

If a structure is located along a line without any rotation (SO = 0 in Fig. 7.3-7) its transverse axis is always oriented in the direction of positive line offsets (positive offsets are to the right as you march along the line in the direction of increasing stations). Therefore, without rotation, the structure at the top left of Fig. 7.3-16 (right turn structure) would be used at an alignment point with a positive line angle, while that at the bottom left of Fig. 7.3-16 (left turn structure) would be used at a negative line angle.

-

SA

If the allowable swings (in degrees) for the right turn structure were:

Condition 1: SAmin = 20 SAmax = 40
Condition 2: SAmin = 15 SAmax = 50
Condition 3: SAmin = 10 SAmax = 60

Those for the left turn structure would be:

Condition 1: SAmin = -40 SAmax = -20
Condition 2: SAmin = -50 SAmax = -15
Condition 3: SAmin = -60 SAmax = -10

Using only one unsymmetrical structure

When you look closely at the two structures at the left of Fig. 7.3-16 you will note that they are almost identical. If you rotate the right turn frame 180 degrees about its centerline it looks like the left turn frame, except that the phases (numbers at the top of the frames) are reversed. Therefore, if you rotate the right turn frame, you will need to transpose the attachment points of phases 1 and 3, otherwise the outside phases will cross-over in the adjacent spans. Phase transposition is discussed in Section 10.3.1.

If you only have one unsymmetrical structure model (right or left turn) and use spotting optimization as described in Section 14, the following algorithm is used: 1) the structure is declared a right turn structure if the absolute value of SAMAX (see Fig. 7.3-16) is larger than the absolute value of SAMIN. It is declared a left turn structure otherwise, 2) Right turn structures are used at positive line angles. At negative line angles, they are rotated 180 degrees with -SAMAX becoming SAMIN and -SAMIN becoming SAMAX, 3) Left turn structures are used at negative line angles. At positive line angles they are rotated and the allowable swing angles are changed as in 2) above. Once the optimization is completed, you may need to manually transpose phases to avoid cross-overs.

7.3.17 Wind & Weight Spans Report

With Lines/ Reports/ Wind & Weight Spans you can generate a report containing the weight spans of specified structures for as many combinations of weather cases and cable conditions as you enter in the Criteria/ Wind & Weight Span Report table.

7.3.18 Blowout and Departure Angles Report

The function Lines/ Reports/ Blowout and Departure Angle Report described in Section

11.2.3.3.1 is used to check departure angles and maximum wire blowouts (measured as offsets) for a range of structures for the combinations of weather and cable conditions specified in the Criteria/ Blowout and Departure Angles table. For these combinations, PLS-CADD systematically applies the wind perpendicularly to the span involved and in both directions, i.e. the span is swung out in two opposite directions.

7.3.19 Default Wire Temperature and Condition

Data in the Default Wire Temperature and Condition dialog box are explained in that dialog box. You reach it with Criteria/ Default Wire Temperature and Condition.

7.3.20 Finite Element Modeling Data

You will only need to enter data in the SAPS Finite Element Sag-Tension dialog box (see Fig. N-5), which you reach with Criteria/ SAPS Finite Element Sag-Tension, if you use Level 2, 3 or 4 modeling as described in Section N.3.

8. STRUCTURES

8.1 General

One of the very powerful and unique features of PLS-CADD is its ability to treat structures as "objects" which can be located, deleted or moved on the terrain at the click of the mouse. The "structure object" contains not only the information necessary to locate in 3-Dimensions all the cable attachment points, but also some pointers to the algorithms or programs which will check the structure strength at its particular location. PLS-CADD currently supports four different methods of checking structure strength. The "structure object" is described in a structure file. The structure file therefore concentrates in a single location all the geometric and mechanical design information that pertains to a given structure type and height. The structure file also

contains data on its insulators and its various parts and subassemblies.

8.2 Structure Top Geometry

In order that the positions of any point on any cable in any span be known in 3Dimensions as a structure is added or moved, it is necessary that the lengths of the devices connecting the cables to the structures at the end of each span (clamps and insulators) and the locations of the attachment points of these devices to the structures be well defined.

For Method 4 structure models developed with the TOWER or PLS-POLE programs, the structure attachment points and the insulators are identified as part of building up the models. Therefore, their positions relative to the base of the model are

T

determined automatically.

L

For Method 1, Method 2 or Method 3

ATTACHMENT SETS SET #1 SET #2 SET #3

THIS EXAMPLE SHOWS SEVERAL PHASES PER SET

IT IS MUCH BETTER TO
ONLY HAVE ONE PHASE
PER SET

structures, you need to describe the ^{Fig. 8.2-1 Structure Top Geometry} positions of the structure attachment points and the geometric properties of the attachment devices (clamps and insulators) relative to the base of the structure. Collectively, these attachment points and the attachment devices form the structure top geometry. For example, the top geometry of the tower in Fig. 8.2-1 includes the structure attachment points (solid squares, triangles and circles) and the associated devices (clamps for the ground wires, suspension insulators for the circuit on the left and V-string insulators for the right circuit).

8.2.1 Cable Sets

A cable "set" (also referred to as a tension section) is defined in PLS-CADD as a group or ensemble of one to three cables (also called phases) with identical mechanical properties and tensions. For example, an electrical circuit between dead ends is often modeled as one set. Corresponding to cable sets are sets of structure attachment points and insulators (or attachment devices). For the tower of Fig. 8.2-1, the two ground wire attachment points and attachment devices were made part of Set #1, the three conductors in the left circuit and their suspension insulators were made part of Set #2 and the three conductors in the right circuit and their V-String insulators were made part of Set #3. If two different cables of the same circuit are not sagged at the same tension then they should be made members of different sets. The only reason for grouping wires together in a set is that come stringing and sagging time you can string the wires through all the attachment points within the set and sag these wires simultaneously. If on the other hand you put each wire in independently (3 sets of one wire) then you will need to repeat the stringing and sagging operation three times, once for each set. However, even with the time penalty associated with modeling only one wire per set, there is the advantage of being able to sag each phase separately. We recommend modeling only one wire per set as illustrated with the wires of the Demo line.

When a set has more than one cable (as illustrated with the WPLFULLM example or in the tower model of Fig. 8.2-1), each cable is identified by a "phase" number and its structure attachment is identified by an "attachment" number. There can only be one, two or three phases per set, therefore the "phase" or "attachment" numbers can only be 1, 2 or 3. When you string a circuit, you have the ability to take any "phase" and attach it to any structure "attachment". This allows you to transpose phases at intervals along your line (see Section 10.3.1 for more details).

For Method 1, Method 2 and Method 3 structures, the positions of the structure attachment points are described in a local coordinate system (x,y,z) located on the vertical axis of the structure, such that the local x axis is in the general direction of the structure transverse axis, the local y axis is vertical and oriented downward, and the local z axis is in the general direction of the structure longitudinal axis (see Fig. 8.2-1). The origin of the (x,y,z) system is at a point denoted TOP. The TOP point should be located on the structure vertical axis, at a distance HT (defined as the structure height) above the point BS defined as the structure base point. It is convenient, but not necessary, to locate TOP at the same elevation as the highest point on the structure. Locating a structure on the terrain involves pinning point BS on top of a terrain point P, or at a specified station along the profile. The structure can also be rotated about its vertical axis by its orientation angle SO, as shown in Fig. 7.3-7.

8.2.2 Clamps and Insulators

At each of the structure attachment points of a set, one connector or insulator type must be defined. Available attachment devices are: 1) clamps, 2) strain insulators, 3) suspension insulators, 4) V-strings or 2-parts insulators, and 5) post insulators. When devices have specified wind areas, the wind load on them is calculated as the design pressure times that wind area.

Clamps have no geometric dimensions, i.e a cable attached to a structure with a clamp passes exactly through the structure attachment point.

Strain and suspension insulators have length, weight and wind areas. In addition, suspension insulators have minimum and maximum allowable swings as described in Section 7.3.17.

V-strings and 2-parts insulators include two sides, each having length, weight and wind area, and the ability to take compression or not. In addition, such insulators have minimum and maximum allowable load angles as described in Section 7.3.17.

Post insulators are handled differently when attached to Method 1, Method 2 or Method 3 structures as opposed to Method 4 structures. With Method 1, Method 2 and Method 3 structures, post insulators have weight but no geometric dimensions. Instead, you need to define the location of each insulator tip where the conductor is attached. With Method 4 structure, post insulators have geometric dimensions, as they are cantilevered from structure attachment points.

One of the reasons we have elected to include insulators as part of a structure top geometry in PLS-CADD is that their allowable swings or load angles (see Section 7.3.17) are specific to the actual geometry of the structure to which the insulators are attached.

8.2.3 Tension Sections

A "tension section" in PLS-CADD is defined as a cable set, in one or more spans, between dead ends. A section always starts at a dead end (a point which cannot move), it may be supported at intermediate points by suspension, 2-parts or post insulators that may move in the longitudinal direction, and it always terminates at its other dead end. Each tension section has its own ruling span (see Appendix I), which depends on the geometry of all the spans between dead-ends.

With the Ruling Span method (Level 1), the horizontal component of tension is assumed constant over each span of the tension section. With the more accurate Finite Element modeling (Levels 2, 3 and 4), horizontal tensions in each span may be different and are calculated by analysis. But with either method, each tension section behaves independently of any other tension section.

Therefore, PLS-CADD needs to be able to identify the beginning and end of each tension section from information in the structure files. This is provided by a simple check ("Section End" in the Insulator Data dialog boxes of Section F.1.1) regarding whether a particular attachment point is dead-ended (section end) or not. Attachment points of Suspension, V-strings and 2parts insulators are obviously not section ends. Attachment points of strain insulators are section ends unless the structure is very flexible. Attachment points of clamps and post insulators can be sections ends or not. This requires engineering judgment. For example, tensions on each side of a flexible post insulator (or on each side of a clamp at the top of a wood pole) may be assumed equal (Level 1) or related (Levels 2, 3 or 4) and are therefore not section ends. However, if the post insulator (or the clamp) and the supporting structure are rigid, the tensions on either side are somewhat independent and you could assume a section end when using Level 1 modeling. The ability of Level 2, 3 or 4 modeling to account for the stiffness of the attachment point allows for a better modeling than Level 1 which can only handles situations where an attachment point is either totally free to move or totally fixed,

In summary, any structure model used in PLS-CADD should include a minimum of top geometry information, that is, for each cable set: 1) the clamps and insulator properties, 2) the locations on the structure, relative to its base, where the clamps and insulators are attached, and 3) whether the attachment points of the cables to the clamps and insulators are ends of tension sections. With that information, the structure can be treated as a 3-dimensional object which, once located on the terrain, will completely define the 3-D locations and nature of the support points of each cable in each span.

8.3 Structure Strength

There are four different methods for describing the strength of a structure in PLS-CADD. The particular method which should be used is specified in the structure file. Therefore, when a structure is selected from the library of available structures, the method by which the structure will be analyzed for strength adequacy is already prescribed.

8.3.1 Method 1 - Basic Allowable Spans Method

Method 1 is the simplest method. It is used in traditional manual spotting and by most automatic spotting programs. It relies on the most elementary concept of actual and allowable wind and weight spans. The actual wind (or Horizontal) span at a structure, HS, is the average of the chord lengths of the spans to the left and right of the structure. The actual weight (or Vertical) span, VS, is approximately equal to the horizontal distance between the low point in the left span to the low point in the right span as discussed in Section I.3. Low points can be within the spans or outside. Since the locations of the low points move under different weather and cable conditions, the vertical span must be defined with reference to a combination of weather and cable conditions. For each of several weather and cable conditions, say 1) bare conductor under extreme wind, 2) bare conductor cold and 3) conductor coated with ice, there are maximum or minimum allowable values of wind and weight spans that have to be met in order to avoid violating a structure strength or serviceability criterion.

The actual implementation of

Method 1 in PLS-CADD is summarized in Fig. 8.3-1. For a range of line angles, allowable values HSMAX, VSMAX1, VSMAX2, VSMAX3 and VSMIN are prescribed in the structure file, respectively for: 1) the maximum wind span, 2) the maximum weight span for HS _MAX HS _MAX HS _MAX Condition 1, 3) the maximum weight span for Condition 2, 4)

_{the maximum weight span for} VALID FOR GIVEN RANGE OF LINE ANGLES

^{Condition 3, and 5) the minimum} Fig. 8.3-1 Allow. Regions for Wind & Weight Spans (Meth 1)
weight span, regardless of
condition.

Typical choices for Conditions 1, 2 and 3 have been:

Extreme wind with no ice, extreme cold with no wind and no ice, and extreme ice (most common)

or Extreme wind with no ice, extreme cold with no wind and no ice, and NESC Heavy condition

or NESC Medium condition, extreme wind with no ice, heavy ice with small wind etc.

Actually, you can use the same condition several times (two or three times), for example:

NESC Heavy condition, NESC Heavy condition, extreme cold with no wind and no ice

The strength of the structure is adequate if the combinations of actual wind and weight spans for the three conditions fall inside the corresponding shaded regions of Fig. 8.3-1. The actual wind and weight spans calculated by PLS-CADD for the comparisons with allowable values are based on the cables in the heaviest cable set, or on the cables of a designated set in the case of spotting optimization.

In general, maximum allowable weight spans for conditions with some ice are shorter than allowable values for bare conductors (extreme wind on bare conductors or cold). In addition, actual weight spans for conditions with ice are generally shorter than those under bare conductor cases. This is one of the reasons we allow you to make use of three separate allowable weight span values instead of a single one valid for all possible load cases.

There are several shortcomings to Method 1, the most serious being the fact that allowable wind and weight spans for a structure are not intrinsic properties of the structure alone: they depend on the design criteria, cable conditions, and the number, type and mechanical tension (for angle structures) of all attached cables. If a designer upgrades a conductor to a different size or changes a climatic design criterion, the allowable span values are no longer valid.

Therefore, in upgrading or assessment projects, the allowable spans method is not desirable. The other problem with the basic allowable wind and weight spans method is that it ignores possible interactions between the allowable spans. For example, a single pole supporting a short weight span has a larger allowable wind span than when it supports the maximum design weight span. The difference, mostly caused by the P-Delta effect, can exceed ten percent, causing some inherent capacity to be overlooked. In order to take advantage of allowable spans interaction, Method 2 can be used.

8.3.2 Method 2 - Allowable Spans Interaction Diagram Method

With Method 2, an interaction diagram between allowable wind and weight spans is defined for certain combinations of weather and cable conditions. For example, Fig. 8.3-2 shows an allowable interaction diagram (Line 1-2-3- ..) for a given combination of weather and cable conditions. The actual wind and weight spans corresponding to the condition are calculated. If their combination falls inside the interaction diagram, then the strength of the structure is adequate for the condition.

1

^{The use of Method 2 structures can} Fig. 8.3-2 Wind & Weight Spans Interaction

produce more economical lines than with Method 1 structures, especially when used in conjunction with automatic spotting. Establishing interaction diagrams may be difficult, unless you have access to structure programs such as TOWER and PLS-POLE which can determine them automatically for you. Currently, for automatic optimum spotting with PLS-CADD, only Method 1 or Method 2 structures can be used. This was done because only these methods provide a sufficiently fast structure strength check. Optimization algorithms require strength checks for possibly billions of combinations of structure locations. However, for assessment and upgrading projects, Method 3 (not recommended) and Method 4 (recommended) are much more desirable.

8.3.3 Method 3 - Critical Components Method

Method 3 structures were fully supported in earlier versions of PLS-CADD and we still support them for backward compatibility. However, for new projects, we recommend that Method 3 structures not be used. For detailed information regarding Method 3, you should consult an older version of the PLS-CADD manual.

Method 3 structures were used as substitutes for Method 4 structures when a full structural analysis was prohibitive in term of time and memory requirements. The simplified Method 3 model utilized a matrix of influence coefficients relating forces and moments in the "critical components" to unit loads at the structure attachment points and it required your input of the design strengths of these components. The method was only valid for linear structures.

However, with the availability of efficient programs such as TOWER or PLS-POLE which can now perform an accurate structure analysis and design check in a fraction of a second (or a few seconds for a very large nonlinear tower with thousands of members) the need for Method 3 structures no longer exists. With Method 3 structures you could not: 1) use V-strings or 2-parts insulators competently, 2) model nonlinear structures such as flexible poles for which the P-Delta effect is significant or any guyed structure, 3) easily modify member properties or gain intuition as to the original structure model, 4) obtain structure deflections, and 5) display the structure with components color-coded by percent strength utilization. Therefore, for these reasons and others, Method 3 structures are obsolete.

8.3.4 Method 4 - Detailed Structural Analysis Method

Method 4 is used if you want PLS-CADD to check the strength of your structure using our TOWER or PLS-POLE programs. When a structure is selected for checking, PLS-CADD determines its design loads and passes them to the appropriate program. The program then analyzes the structure, checks its design and returns detailed reports and graphical summaries (such as color coded deflected shapes) to PLS-CADD. The entire process is automated and should not take more than a second or two. Method 4 is by far the best method for checking an existing line. It is the most general and accurate of all methods. For example, the wood frames in Fig. 8.3-3 were modeled as Method 4 structures with the PLS-POLE program. The analysis results shown as percent utilization (in the right window) were obtained automatically for all load cases within a second of clicking on the frame in the line (in the left window). The lower smaller window shows the deflected shape exaggerated by a factor of 5.

As mentioned above, when a Method 4 structure is used, its loading tree is first determined by PLS-CADD which passes it to the TOWER or PLS-POLE program for the analysis and check of the structure. The loading tree is determined for a certain number of weather and cable conditions, together with appropriate load factors as discussed in Section 7.3.12.

Conventionally, loading trees include force components which are determined either at: 1) the attachment points of the cables to the insulators (for example at the lower ends of suspension or V-string insulators shown in Fig. 8.2-1, or 2) at the attachment points of the insulators to the structure (as illustrated in Fig. 8.3-4 for the tower of Fig. 8.2-1). For suspension insulators, the trees are identical, except for the weight of the insulators and the wind forces on them. For post insulators, moments are generated at the structure attachment points, so the two trees are quite different. For V-strings and 2-parts insulators, the design loads V, T and L at the conductor end of the insulators have to be resolved into loads at the structure attachment points. This is

T

a complex task, involving nonlinear calculations, which are handled automatically by our TOWER

and PLS-POLE programs. Loading trees also _{Fig. 8.3-4 Structure Attachment Loads} include the transverse and longitudinal pressures acting on the structure itself.

Because of the two possible ways in which loading trees can be defined, it is important that you understand what is being done in PLS-CADD.

When PLS-CADD exports a loading tree to TOWER or PLS-POLE to check a Method 4 structure or create a loading tree file with Structures/ Loads/ Write LCA file, the tree includes the factored loads at the connections of the cables with the insulators to which the factored weight of the connecting insulators and the insulator wind loads are added. This means that for a V-string or a 2-parts insulator, the tree includes the factored loads at the junction between the conductor and the two sides of the insulator to which we add the total weight of both sides of the insulator and the wind loads on both sides. Therefore, for V-strings and 2-parts insulators, there is no resolution by PLS-CADD of the loads between the two structure attachment points, i.e. the loads which you see displayed for the right circuit of the tower in Fig. 8.3-4 are calculated by TOWER or PLS-POLE automatically from the loads at the bottom of the V-strings generated by PLS-CADD.

When you use the command Structures/ Loads/ Report in PLS-CADD, the report which is generated includes factored loads in the span coordinate system and loads in the structure coordinate system. Loads in the structure coordinate system include the factored weights and wind loads of the insulators.

One of the very unique and powerful capabilities of our TOWER and PLS-POLE programs is that they can automatically determine the allowable wind and weight spans of a structure, given some loading criteria and attached conductors. With this capability, they are capable of generating Method 1 or Method 2 structure files automatically. The only reason for doing this, since you have already developed the superior Method 4 model, is if you are going to perform some spotting optimization which requires the allowable spans model, or if you want to create libraries of standard structures rated by their allowable spans.

A detailed technical note describing the optimization process and the creation of Method 1 structures may be found at http://www.powline.com/products/optimization.html .

8.4 Structure Display

The appearance of a structure in the Available structures report or in a 3-D view depends on how the structure model was generated.

Structures/ Available Structures list/ Report.

8.4.1 Method 1, 2 and 3 Structure Files Generated Directly

If you create or edit a Method 1, 2 or 3 structure file directly with the Structures/ Create New Structure or the Structures/ Edit Structures menus as described in Appendix F, there is no information regarding the detailed geometry of the structure apart from its minimal top geometry described by the cable attachment points. Therefore, you will not see a graphical outline of these structures in the Available structures report and you will see these structures displayed as minimal stick structures in 3-D views. A stick structure includes a vertical line along its vertical axis and horizontal lines going from the vertical axis to any cable attachment point which actually supports a cable. If no cable is strung yet, you will not see the horizontal line.

For example, the right side of Fig. 8.4-2 shows the outline of a minimal Method 1 double circuit structure in a 3-D view.

8.4.2 Method 1, 2 and 3 Structure Files Created by PLS-POLE or TOWER

If you first create a structure model with PLS-POLE or TOWER and use it to generate a Method 1, 2, or 3 structure file, then a detailed line representation of the geometry of the structure is known and is appended to the file for display. This line representation is also displayed in the report of Fig. 8.4-1 or in the Structure File Open and File Selection dialogs.

8.4.3 Method 4 Structures

Method 4 structures are always displayed in detail, including their guys if any. See for example the steel pole at the left of Fig. 8.4-2 and the tower at the center of that figure. You can display Method 4 structures realistically with their material color if you select Color and Texture PLSPOLE and TOWER Structures... in the Line Display Options dialog box of Fig. 5.4-4. Otherwise, they are displayed as "lines", or as "wire frame" or "rendered" (the terminology is described in the TOWER and PLS-POLE manuals) if you select "Unrendered triangle outlines" or "Render triangles" under Terrain/ TIN/ Display options.

8.5 Structure Parts and Assemblies

PLS-CADD includes powerful functions to manage material databases and generate a variety of part or assembly lists. These material handling capabilities are an important factor in improving a user's productivity. Parts and assemblies are defined in master parts and assemblies databases that are normally maintained by a company independently of PLS-CADD. If these databases include ODBC drivers, such as most commercial databases (Mircrosoft Access, Oracle, IBM DB2, Informix, Sybase, etc.), they can be linked directly to PLS-CADD as described in Appendix M.

In order to use the parts and assemblies capabilities of PLS-CADD, you first need to populate the databases as described in this section. Then you need to describe in the structure files which parts and assemblies make up the structure. This process is described in Appendix F. Finally, if some parts and assemblies are not always associated with a specific structure, but are to be used at a particular structure site (for example special foundation material, fences, guys, dampers, extra labor units, etc.), such "structure instance" material is specified in the Structure Modify dialog box described in Section 10.2.2. If parts and assemblies are described at structure locations and/or in structure files, then the complete project material list is automatically generated in the form of a report or a staking material table (see Section 12.3.2). This material table can automatically be linked to commercial data bases and work order systems (see Appendix M).

8.5.1 Master Parts List

Parts and assemblies are included together in the Parts/ Assembly Library file named in the File/ Preferences menu. Part lists files have the ".prt" extension. You can view and edit the parts table with Structures/ Material/ Edit Part List (see Fig. 8.5-1). A parts table includes as a minimum three columns for Stock Number, Description and Unit price. In addition, with the

Structures/ Material/ Setup menu, you can add any number of columns to the parts table. For example, in Fig. 8.5-1, columns were added to list the names of Vendors, etc. For each part there is a unique ASCII Stock number and its associated description. Parts can be labor units, for example basic, semi-skilled, or skilled labor units.

8.5.2 Master Assemblies List

Fig.8.5-2 Master Assemblies Table

Each assembly has a unique assembly stock number, a description, and a list of the parts and/or assemblies needed to construct it. The assembly table is edited with the Structures/ Material/ Edit Assembly List menu. You select a particular assembly in the Assembly table by clicking on it (for example Assembly TP34-4 in Fig. 8.5-2). Then you click on the EDIT button at the bottom of the table to open the Assembly Editor dialog box where you select how many of which part of pre-existing sub-assembly make up the assembly. The cross arm Assembly TP34-4 in Fig. 8.5-2 is made up of 2 wood timbers, 4 braces, 2 brackets, etc.

8.6 Creating, Editing or Customizing Structure File

Creating and editing structure files is described in Appendix F. Customizing them is described in Appendix P.

8.7 Summary of the Advantages of Using Method 4 Structures

For more than a decade many PLS-CADD users have taken advantage of Power Line Systems' advanced structural analysis solutions. Fully modeling structures in our TOWER and PLS-POLE

144 PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008 programs (i.e. using real models of Method 4 structures) provides many benefits over traditional wind & weight span approaches (i.e. using Method 1 or Method 2 structures). These benefits accrue because the intrinsic (physical) properties of a Method 4 structure are modeled separately from the wires which are attached to the structure and the safety code which is used to determine its allowable strength. With a Method 4 structure, a load is applied to the structure and a safety code is then used to check that structure. With Method 1 or Method 2 structures strength is defined by allowable wind and weight spans which have embedded within them the number, type, tension and line angle of the supported conductors as well as the applicable safety code. Modeling the intrinsic properties of a structure separately as opposed to combining these properties with the wires attached to the structure and the code used to check it has overwhelming advantages in the following common design situations:

Reconductoring: When you are using Method 4 structures you simply change the wire or tension and use the Structure/ Check command. With Method 1 or 2 structures you need to compute allowable wind & weight spans (not a simple task) and create new structure files for every combination of conductor, tension and code scenario you want to consider before you can check structures.

Structure upgrades: When you check a Method 4 structure, the program actually checks each piece of the structure. It will tell you which, if any, parts of the structure are failing. A wind & weight span check of a Method 1 or 2 structure will tell you if it is failing but doesn't give you any idea why or what could be done to fix the problem. For example: we once performed an uprating study that involved reconductoring the latticed towers of the line shown in Fig. 5.4-9. These structures did not have sufficient strength for the heavier conductor. PLS-CADD (automatically calling TOWER internally) quickly generated color coded graphics showing the overstressed members. Many of the structures could be made to withstand the load by simply replacing four hanger members. The identification of the members needing reinforcement is not possible with a wind & weight span analysis and in this case resulted in substantial savings over replacing the entire structure.

Changing ruling span: Sometimes, through unusual terrain or clearance requirements you end up with a design that doesn't match the design ruling span very well. Once again, this isn't a problem for Method 4 structures as you just use the Structure/ Check command. For Method 1 or 2 structures you need to re-derive your allowable spans if you really want to get the most out of your structures.

Underbuild/ Joint Use: With Method 4 structures, you simply add attachment points to the structures if they aren't already there string whatever additional wires are needed at the appropriate tensions and use the Structure/ Check command. For Method 1 or 2 structures you need a re-compute different sets of allowable wind & weight spans for each different underbuild scenario.

Unbalanced ice, broken conductors, slack removal/shift for extra clearance: All these situations leave you with a longitudinal imbalance. With Method 4 structures it is very easy to figure out if the structures can withstand this imbalance, even accounting for the interaction between the wires and the effect of structure flexibility. Method 1 or 2 structures are useless in these cases.

Changes in safety codes: Simple code changes can invalidate all your Method 1 or 2 structure models while they do not affect Method 4 structures. For example:

The 2002 revision of the NESC redefined wind pressures as a function of span length and attachment elevation. Those who used Method 4 structures simply switched to NESC 2002 wind adjustments in PLS-CADD's Criteria/ Weather table and performed a structure check. Those who used Method 1 or 2 structures had to re-derive all their allowable wind & weight spans and redo their standards. In fact, the very concept of being able to compute an allowable wind span for a structure seems at odds with the new NESC where you can't even compute the wind unless you know the heights of the ahead and back structures.

Three months after the new NESC took effect, ANSI O5.1-2002 was released which mandated a reduction in the allowable fiber stress for wood poles. Once again, existing standards with Method 1 or 2 structures were rendered useless, but users of Method 4 poles simply switched to the ANSI O5.1-2002 strength check and immediately had updated results.

These two code changes which both occurred in 2002 show why it is so important to model the intrinsic properties of the structure separately from the code used to check it.

Structure modification: PLS-CADD lets you customize Method 4 structures by dragging guy anchors around. It also lets you move attachments and/or arms up and down on Method 4 poles. When you are finished with these drag/drop operations you can check the structure with a simple Structure/ Check. When using Method 1 or 2 structures you have to once again rederive the allowable span values based on the changes to the geometry.

Improved graphics: When using Method 4 structures PLS-CADD can insert rendered images of the structures into its views. These graphics are a great help in catching structure modeling errors. With Method 1 or 2 structures no graphical double check is available.

Clearances to structures/ guys: Method 4 structures graphics are much more than just pretty pictures. These graphics contain all the information PLS-CADD needs to perform clearance checks from wires to the structure and its guys. Method 1 or 2 structures do not contain this information (in fact they don't even specify whether the structure is a lattice tower or a wood pole or even if it has guys).

Maintenance: PLS-CADD allows you to track changes to Method 4 structures and account for deterioration of the structures. For example if your maintenance crew tells you that a wood pole has some shell rot you can model that and immediately check the structure to see if it needs to be replaced. With a Method 1 or 2 structure you have no means to determine the adequacy of the structure.

Phase transposition: When switching from a horizontal to a vertical configuration, each wire in a circuit has its own wind & weight span as well as its own induced line angle. You need to keep this in mind and manually account for it when using Method 1 or 2 structures, but it is handled automatically if you use Method 4 structures.

Generation of allowable wind & weight spans: Allowable wind & weight span values or an interaction of these (which we call interaction diagrams) are currently still necessary for the optimum spotting of a line by PLS-CADD. Therefore, optimum spotting still requires the use of

146 PLS-CADD – Version 9.3 © Power Line Systems, Inc. 2008 Method 1 or 2 structures. However, TOWER and PLS-POLE can use Method 4 models to generate corresponding Method 1 or 2 models with the click of a mouse thus giving you the freedom to rapidly experiment with many different structure and conductor configurations.

The preceding situations illustrate the many advantages of using real structure models rather than allowable wind & weight span models. Wind & weight span models used to be popular in the days of design on paper with pencils and physical templates because they enabled "structural analysis" by simply measuring a few distances on a drawing. They are still useful in low voltage distribution line design where standardization is essential. However, wind & weight span models do not lend themselves well to modern demands on engineering.

9. GROUND WIRES AND CONDUCTORS

9.1 Mechanical Model

The mechanical model adopted in PLS-CADD for cables (ground wires and conductors) can be used to calculate sags and tensions according to most world practices. In many European countries, it has been traditional to assume that cables are elastic, with creep accounted for by an equivalent temperature increase. In North America, non-linear models are the norm, as pioneered by the Aluminum Company of America (Batterman, 1967) and the Bonneville Power Administration (Reding, 1976). The model used in PLS-CADD can be applied to both situations. It is based on original algorithms (McDonald, 1990; SAG-TENSION, 1990) which use polynomial stress-strain relationships similar to those used by the aluminum industry in the USA and Canada (Batterman, 1967; Aluminum Association, 1971; EPRI, 1988, Thrash, 1994).

The condition of a cable within a few hours of its being installed in a transmission line is called its "