By Kathleen Davis, Associate Editor
Remembering the “good old days” has become a national pastime. We long for the uncluttered suburban homes of the 1950s or even the rock-and-roll freedom of the 1970s. But, not everyone looks at those “good old days” quite so fondly. One group of T&D experts recently told us that they’d like to keep the old “pencil and paper” method of T&D siting and design where it belongs: in old faded photographs and distant memories.
UA recently spoke with a group of engineers and managers at GAI Consultants, a multi-disciplinary engineering firm with offices throughout the mid-Atlantic United States. In the area of transmission lines, GAI offers client engineering services from line route selection and permitting through design to construction services.
UA: How did more powerful computers and software products impact the tradition of transmission line siting?
Bob Houston: Essentially, back in the good old days, we had to use paper maps and aerial photography, and they were always at different scales. Sometimes we were working with five or six different scales. It would take a great deal of time and effort to merge all the required data to the same scale and map resources and siting issues within the routing study area.
Then the process was to use acetate overlays over the photography or maps. We would place sensitive resources, other avoidance areas and alternative transmission line routes on the overlays. Generally, we’d start with one- or two-thousand-foot-wide corridors that would look suitable for siting a transmission line. The corridors were then evaluated for suitability. The right-of-way for the line would then be located within the most suitable corridor.
With the introduction of more powerful computers and software programs for this field, we have greatly accelerated the process and are able to bring in a lot more data because of the availability of digital topographic and resource mapping and digital aerial photography. We can now set the digital scale to a single working scale and bring all this data together very quickly. Of course, we still have to field check once we have corridors in the software. We use GIS software to do the mapping and the data management.
Some readers may not realize it, but GIS is a good-to-great graphics package with terrific data management capability. It’s definitely the way to go in this business today.
UA: Let’s talk about the process used for surveying and designing new lines before and after the introduction of computer-aided design and drafting (CADD).
Ron Ponist: Before CADD, the line was laid out on U.S.G.S. maps, and then the survey corps would locate, or stake, the angle points in the field. Then the engineer would make a field evaluation of the angle point structure locations and road crossings. Next, the survey corps would survey the centerline and obtain elevations of the proposed route and also obtain offset elevations some distance on the right- and left-hand side of that center line–say approximately 30 feet. Then this survey information was transcribed by hand by a technician onto profile graph paper, and these sheets were then given to the engineer who would spot the towers by hand, using templates that represent the catenary curve of the conductors.
John Mozer: Today this is a much more fully automated process of surveying, collecting data and importing it into the computers, and, in many ways, almost fully automatically spotting structures and optimizing structure locations based on cost and structure strength. For example, in the survey area, there has been a huge improvement with digital cameras and laser devices that are mounted on helicopters. So that, at the same time they get the aerial photography, they also get unbelievable amounts of point data to completely define all of the ground features and the ground data–the X,Y coordinates of each point and the elevation.
Then, all of this information can be directly imported into the computer. With the line-design software that is available today, the engineer can sit down at a computer work station and set up the alignment of the line very quickly–using a “point and click” method. Optimization procedures are built into the software to automatically spot the structures and sag the conductors between the structures. Once that is finished, the computer can automatically export drawings of the plan and profile data. It’s a total revolution of how we design transmission lines from what was done in the past.
UA: Was there one area of design that was particularly cumbersome and difficult before automation took over the process?
Bob Houston: For both design and siting, there were extreme problems with the old method when changes occurred. Prior to computerization, if there was a shift in the alignment, we would have to go back and measure all of the potential impacts of the changed area, which could take quite a bit of time.
John Mozer: In the design area, change was also one of the most cumbersome things, especially when that change occurred to the alignment of the transmission line. In the past, if you had to make a significant move of a structure–particularly one of the angle point structures–you’d have to go out and redo the survey information. This would be brought back into the office, and the engineer would have to go through the whole structure spotting process again. Whereas now, with digital computers, if the field people decide they have to make a change in a structure location, all they have to do is send the engineer an e-mail with the coordinates of the new location and by the “point and click” process, in a matter of seconds you can relocate the structure in the computer model and get everything refigured automatically.
UA: What are the major differences in time, and what are the digital advantages in a paper vs. computer transmission design comparison?
Tony DiGioia: It’s really getting to the point where we can easily achieve the tight schedules that are imposed on us by our clients. The ability to quickly process economic changes saves us and our clients time and headaches. For example, an analysis of the impact of an alignment change can be performed quickly without the necessity of any additional surveys. No way in the world could we have handled right-of-way acquisitions on the fly in the old days.
UA: Are there any disadvantages to all this automation?
John Mozer: A couple come to mind. With the use of computers and digital data, you end up with a huge amount of data that has to be manipulated. So, one disadvantage is that we are constantly having to upgrade our hardware. Bob Houston’s GIS department is driving our IT people nuts with that. Another possible disadvantage is that there is always the danger of misapplication. Computers make it very easy to sit down at a work station and do this, and there can be a danger of losing a physical feel for what you’re doing. The line design software is very powerful, but still requires a skilled user.
Tony DiGioia: Let me add to that. With respect to foundation design, there are several really good computer programs out there, and we have developed several of them. But, we’ve written them so that the geotechnical input parameters–like the density of soil–aren’t entirely open. We give a range for each parameter that would make sense. Now, if someone puts in 10 pounds-per-cubic-foot instead of 100 pounds-per-cubic-foot, which is the right order of magnitude for soil density, then the computer beeps and tells the designer that the input parameter is outside of the range of expected values. So, you can warn the designer about certain unrealistic values for input parameters, but you cannot stop someone who has little judgment and thus doesn’t know whether the density is 100 or 130, because both values are within the range of reasonable values. So, the engineers who use these programs need to have the judgment about proper input parameters and also must be able to look at the output and say, “Yes, those answers make sense.”
UA: What specific features do you look for when choosing software for line surveying and design, and what new features do you anticipate being included in software over the next few years?
Ron Ponist: We look for software that is quality-assured, that is user-friendly–including the ability to import and export data easily. And, also, we look for good technical support.
Bob Houston: We expect the software to become even more user-friendly over the next few years. Also, we’re expecting the software developers to improve the linkage between the various software packages.
John Mozer: Let’s say, for example, you get a design on the computer, and a lot of our clients don’t have that design software, but they have a general purpose computer-aided drafting (CAD) software, such as AutoCAD and MicroStation. Today, you have to export a DXF (drawing interchange file) file from the line design to the CAD software. The problem is, when you do that, you don’t get exactly the same picture. So, you must manually go into the drawing file and make corrections and fix it up. One of the things we really hope to see is a direct linkage between line design software and drafting software like AutoCAD and MicroStation.
Bob Houston is the environmental studies and planning department manager at GAI Consultants. Tony DiGioia is chairman of the board of directors. Ron Ponist and John Mozer are staff consultants in the geotechnical/structural deprtment at GAI.