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Line Optimization is one of the most powerful features of PLS-CADD. It will provide the least-cost solution for spotting a given set of structures for a desired set of design criteria on any desired route. This TechNote is intended to detail the steps that should be done in order to perform an optimization as well as features of the optimization process and even some advanced features after the optimization is complete.
The first step to an optimization is that you must have your route selected in PLS-CADD. Route selection is beyond the scope of this TechNote and is covered in the manual as well as other TechNotes. Please keep in mind though that you could have several projects utilizing the same data in order to optimize numerous routes to get cost comparisons between alternative routes.
The next step to optimization preparation is that you should have the clearances required for the various voltages that you will be using on your line in your Terrain / Feature Code Data / Edit tables. This is the only way to insure that the proper clearances will be met after your optimization is complete.
Several items in your in your Criteria settings should be verified. Insure that the Criteria / Survey Point Clearances table has been completed with any and all conditions that you want to insure that the proper clearances as defined in your Feature Code tables above are maintained - don’t forget to include any cold and/or uplift conditions listed in your Survey Point Clearances in the event that your line design will be going under any aerial obstacles. Select and note the four weather conditions in Criteria / Insulator Swing. It is also strongly suggested that the Criteria / Automatic Sagging table be completed with all the possible desired stringing limitations for the conductors on your line. It will be much easier to allow the program to automatically select the tensions during the actual optimization process than trying to figure out an actual stringing tension at that time.
Now for the most important step in line optimization; the designer must model structures for use in the optimization. In order to do this, one must understand the different methods in structure modeling for PLS-CADD.
Again, the full explanation of these various methods is beyond the scope of this TechNote, but they can be found in Section 8.3 of the PLS-CADD Users Manual. But an important concept to understand is that PLS-CADD can currently only optimize with Method 1 or Method 2 structure models. Unfortunately, computers are just not fast enough yet to allow the millions and millions of structure analyses required for the optimization with Method 4 structures. Perhaps one of these years they will be, but for the current capabilities, Method 1 or Method 2 structures must be used. For the remainder of this TechNote, it will be assumed that the designer will be using Method 1 structures for optimization. There will be a brief discussion at the end of the TechNote for those that wish to utilize the more advanced Method 2 structures.
Of course one could just model Method 1 structures directly using the Structures / Create New Structure function in PLS-CADD (see Appendix F in the PLS-CADD Users Manual.) However, this method has many shortcomings as we will see later, and most designers would be calculating their allowable spans from PLS-POLE and/or TOWER anyway. Which finally brings us to the primary purpose of this TechNote; how do we optimize a line with structures that we have modeled in PLS-POLE and/or TOWER? The process to do this will now be outlined step-by-step. In this process, we will assume that the designer is using wood poles in PLS-POLE, but keep in mind that the process will be nearly identical for any other material of poles or even structures modeled in TOWER.
Now, go to PLS-CADD, go to Structures / Available Structure List / Add/Delete Structure to add all of the Method 1 structures and then Structures / Available Structure List / Edit to assign costs and to determine the other variables for optimization. The four variables that must be determined for each structure are the cost to use for optimization, whether or not use the structure for optimization, the set for optimization, and the minimum line angle.
If you want to automate the pricing, make sure in PLS-POLE you go to Geometry / PLS-CADD / Material Options (and Edit User Entered Material) to build your materials. Then, back in PLS-CADD, in Structures / Available Structure List / Edit, the automated cost from the materials will be available and you can just copy/paste that column to use the developed cost for the optimization cost.
Now that we have told PLS-CADD what structures are available for the spotting and the cost basis for doing so, the second process that needs to be completed before optimization is determining where structures can and cannot be placed, and extra costs associated with doing so, and where any specific structures must be used. These constraints can all be added (and deleted) under Structures / Automatic Spotting / Spotting Constraints. It is the authors opinion that the / Add (graphical) function should be used as this allows the constraints to be determined much quicker than the alternate Edit (table based) method. (Hint; don’t forget to use the Dynamic Pan/Zoom function (hold the Shift key down and move the mouse) to “fly” around the project to quickly add your constraints.) It is also suggested that constraints be added in both the Plan view to find the obvious constraints such as roads, but also in the Profile view to look for areas where constructability of the line should be considered. A tip that is often not thought of is the use of negative costing for Extra Cost Zones; using a negative price for a region will make that region appear more favorable for spotting. This will not necessarily force a structure to be spotted in this region like the Required Structure constraint will, but it will dictate that structures will gravitate to this area if that is the most economical option. A common misconception is that Optimization is only for rural projects; this couldn’t be further from the truth. With the ability to quickly determine constraints, optimizing in urban areas not only still develops the least cost option, but is also much easier than manually determining the structure locations and heights in these highly constrained areas.
TIP! It might be a good idea to add the Graphical Constraint functions to a Custom Toolbar Button by using View / Edit Customizations / Custom Toolbar. Make sure you have the Custom Toolbar turned on under View / Toolbars / Custom Toolbar.
Once the Allowable Structures and the Spotting Constraints have been determined, you are now ready to optimize. Chapter 14 of the PLS-CADD manual covers the actual optimization process in depth, so it will not be covered here in this TechNote. However, a couple of extra “tips” will be discussed here;
Once the optimization is complete, you can then use the Sections / Automatic Stringing to string all of the other sections of wire, and then the Sections / Table to modify them. It is suggested in the Sections / Table that the Sort Sections By be set to "Attachment Set Section Starts Upon" for easier editing. If this is done, the properties for the first wire in each Attachment Set can be input, and then that row can easily be copied and then pasted for the remaining Attachment Sets in the line. This means a 1000 span line could be completed nearly as fast as just a 1 span line. (It is assumed that the designer has followed the recommendations of using the same set number for all like wires for all structures in a family in order for these options to be used most effectively. If this has not been done, then Sections / Modify / Edit Stringing might need to be used to ensure that the wires are connecting properly to all the structures on the line.)
Note that you can select the "AutoSag" command in the Command To Apply column to have all wires sagged automatically so that they reflect any changes you made in the Sections Table.
If you have used PLS-POLE and PLS-CADD Lite as described above to create your Method 1 structures for optimizing, you can hit the F1 key, choose Use Method 4 Structure Check/Edit When Possible, and you can then check your structures via PLS-POLE instead of the simplified wind-weight spans. Running a Lines / Reports / Structure Usage before doing this will show you the structure usage based on Wind and Weight Span limits. Switching to Method 4 and rerunning this report will show you how conservative the Wind and Weight Span design method is. If the designer feels that this is too conservative for their project, then one might consider using Method 2 (Interaction Diagrams) structures. This is a bit more complex and takes additional time to calculate all of the Interaction Diagrams, but the process is nearly identical as above and can easily be done with both TOWER and PLS-POLE structures.
Finally, as discussed in the Wind & Weight Spans technical note, Wind and Weight span designs have many problems. Using PLS-POLE (and TOWER) with PLS-CADD Lite to develop the Method 1 (or Method 2) structures for PLS-CADD optimization allows the designer to take advantage of the best that both methods have to offer and really completes the "design circle". Toggling to the Method 1 side, one can quickly optimize a line, and toggling to Method 4 will allow a full finite element structural analysis of the structures to be completed. In the event of a conductor change out, this can simply be done (using Sections / Table is the easiest way) and then a full structural check be performed again. Since a conductor or even just a wire change out voids the Wind and Weight span limits of a structure, the Method 1 checks can now be ignored, or, the conductor change out can be made in the PLS-CADD Lite models for each structure type and the Method 1 structures can quickly be regenerated for reoptimizing the line with the revised conductor.
Optimization will easily beat any manual spotting process in overall project costs. In many comparisons done by knowledgeable utilities and consultants, the PLS-CADD Optimization provided the absolute least cost constructed line alternative that met the project design criteria when compared to any other spotting optimization program. Not only does PLS-CADD provide the least cost constructed line cost, the few hours spent setting up the optimization process as described above will save a significant amount of engineering and design time (and therefore money) over any manual spotting process.
While Optimization can appear to be quite complex on the surface, it is actually quite simple once the process is observed. This was covered quite extensively at the last User Group meeting, and will be covered again in future meetings. The User Groups really are free "advanced training” sessions, so we hope that you can make the next one.