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Re-Engineering The Transmission Line Design Process[8/23/2014 1:41:05 PM] Re-Engineering The Transmission Line Design Process Re-Engineering The Transmission Line Design Process Otto J . Lynch, P.E. Black & Veatch. 8400 Ward Parkway, Kansas City, MO 64114 (913) 339-7549 (913) 339-2888 Fax Peter Hilger, E.I.T. The Empire District Electric Company P.O. Box 127, Joplin, MO 64802 (417) 625-5100 (417) 625-5165 Fax INTRODUCTION
  Re-Engineering The Transmission Line Design Process[8/23/2014 1:41:05 PM] Re-EngineeringThe Transmission LineDesign Process  Re-Engineering The Transmission Line Design Process Otto J. Lynch, P.E.  Black & Veatch. 8400 Ward Parkway, Kansas City, MO 64114 (913) 339-7549 (913) 339-2888 Fax  Peter Hilger, E.I.T. The Empire District Electric Company P.O. Box 127, Joplin, MO 64802 (417) 625-5100 (417) 625-5165 Fax  INTRODUCTIONTraditionally, transmission line design practices have been comprised of conservative assumptions which easily model an elaborate and complex structuralsystem. Continued developments in computers and software have given us the capability of breaking these normally inflexible traditions, and have allowed the industry the opportunity to re-engineer the entire transmission line design process. Finally, the seamless integration of all aspects associated withtransmission line surveying, engineering, drafting, procurement, and construction is essential to maximize the full benefits of the re-engineering effort.Black & Veatch (B&V) is an engineer/constructor headquartered in Kansas City, Missouri. The firm has provided engineering, construction, and related services for electric power transmission and distribution throughout its 80-year history. The firm’s Transmission & Distribution Division forms one of thelargest T&D staffs among engineering and construction firms in the United States. By utilizing state-of-the-art resources and techniques, B&V continuallystrives to improve the transmission line engineering, procurement, and construction (EPC) process to produce better designs in the fastest, most economicalmanner.The Empire District Electric Company (E.D.E.) is an independent, investor owned, electric utility providing quality electric service in the four-state area of Kansas, Oklahoma, Arkansas, and Missouri. E.D.E. is dedicated to providing its customers with the highest reliability possible, while maintaining its lowrates.B&V and E.D.E have selected the PLS-CADD software suite developed by Power Line Systems, Inc., Madison, Wisconsin, to support their needs for a better, faster, cheaper transmission line design environment. The line design software selected has the capability of meeting all the objectives required for the full integration of the transmission line design and drafting environment. SURVEYINGRecent developments in surveying technologies have allowed the industry to re-think the station-elevation-offset formats that designers have traditionallyused for transmission line profile modeling. Today’s generally accepted method of surveying is some form of three-dimensional geographical informationsystem (GIS) type representation. Data are usually collected in electronic format, and the transmission line software must be capable of reading the dataintelligently in any form. Total Station, Geographical Positioning System (GPS), Photogrammetry, electronic topographical maps (USGS), and scanned or digitized existing profile drawings have all been employed to develop quick and relatively accurate terrain models for transmission lines.B&V and E.D.E. utilize a state-of-the-art technology, the FLI-MAP™ laser mapping system. FLI-MAP was developed by John E. Chance and Associatesof Lafayette, Louisiana. This advanced technology system incorporates On-The-Fly (OTF) Kinematic GPS, GPS aided attitude, a reflectorless laser rangefinding sensor, and a helicopter to quickly gather topographical and other pertinent aboveground data. This method yields about 10 data points per squaremeter over a 65 meter wide corridor under the flight path. This technology produces points with an accuracy better than 12 cm vertical and 15 cm horizontalof all points on and above the ground. Approximately 100 kilometers of continuous line can be surveyed in a day, and the data can be available in thedesired coordinate system and elevation datum on the same day if dictated by the client. The information can then be directly imported into PLS-CADD in a  Re-Engineering The Transmission Line Design Process[8/23/2014 1:41:05 PM] matter of minutes. Transmission line design can commence immediately using extremely accurate profile, significantly more accurate than even a verydense, time and labor intensive ground survey can produce.The design software selected has the capability of taking any three-dimensional survey format and cutting the profiles. The centerline and up to 20 leftand right profiles at any offsets can be generated and shown. This process is nearly instantaneous, so Points of Intersection (P.I.s) can be moved or added atany time, and the new stationing and profiles are updated immediately. This allows for the typical last minute reroutes to be made quickly and effortlesslywithout delays caused by having to wait for new profile surveying, stationing changes, and engineering modifications. Station equations (equalities) will beobsolete.In addition, the software has the capability of creating interpolated points on these profiles by creating a triangular irregular network (TIN). This TIN canalso be rendered to present a graphical three-dimensional representation of the transmission line, which can be used for permit and public hearingrequirements or any other forum where graphical representations are required of the line (See Figure 1). Figure 1  - Three-dimensional rendering of a double-circuit 500 kV transmission line.  ENGINEERINGA critical component in any re-engineering effort is the simplification and centralization of all activities. In the transmission line engineering arena, all parameters governing any part of the line design should be available in one common package. Engineers cannot and should not be expected to learnmultitudes of software programs, keep current in each of their independent updates, and maintain support with each of the programs. In addition, any datatransfers between such programs, whether manual or electronic, leave room for error. Finally, it is critical that the software be on a computer platform thatis user friendly and commonly accepted across the engineering and   business worlds. Managers, engineers, technicians, drafters, and secretaries should beable to use any form of the programs or their outputs using a common interface, without having to learn complex drafting programs or obsolete operatingsystem languages.Another area of the software used in the re-engineering process that should not be overlooked is that it be technically sound. Software that merely duplicates  Re-Engineering The Transmission Line Design Process[8/23/2014 1:41:05 PM] assumptions and errors of the past is only as good as those assumptions. In today’s computer environment, these programs will allow an error or mistake to be made faster than ever before. It is imperative that all calculations be made using state-of-the-art technologies and methodologies, and to the highest levelof accuracy that is reasonably achievable. These criteria should not be sacrificed in an effort to simplify or expedite the design process.PLS-CADD allows the engineer to completely design and lay out a transmission line without having to use any other external software. Due to thisintegration, all design criteria which will be imposed on the transmission line system are developed in one place. Loads which will be used to develop a sag-tension analysis and check sag clearances, uplift considerations, blowout criteria, cable tension limits, insulator swing criteria, structure design, insulator design, guying design, and foundation design are developed in one place. Overload factors (OLFs) can be applied in the transverse, longitudinal, and vertical directions and on the wire tensions. The loads can be selected to be applied to any component of the transmission line system. This allows PLS-CADD to be adaptable to any code or manufacturer requirement where different OLFs are required for each component of the transmission line system.Structure design and spotting are indicative of the re-engineering effort making tremendous strides. Traditionally, structures have been designed bydeveloping allowable spans, wind and weight, under all the loading cases applicable to the structure. For example, due to terrain factors, a structure familymay be designed for a vertical to horizontal span ratio (H/V) of 1.5. Using this criteria, an example tangent structure may have limitations of a maximumwind span of 300 meters and a maximum weight span of 450 meters, where the maximum wind span was probably dictated by an extreme wind conditionand the maximum weight span was probably dictated by a heavy ice condition. When spotting this structure on a line, either by hand or by less sophisticated spotting software, the structure location is acceptable if the wind and weight spans are both below the allowable span limitations.However, in the real world , the wind and weight spans are rarely maximized simultaneously for any given structure on a line. While we may think that weare maximizing the use of the structure by approaching 100% use of either the allowable wind or weight span, there is actually additional strength availabledue to the contra allowable span not being utilized to its capacity, thus creating an interaction between the allowable wind and weight spans. Coupling thisinteraction phenomenon on a loading case by loading case basis, it can be seen that traditional methods used to spot structures can be as much as 70% or more conservative in their application. The associated reduction in structure costs on a large transmission project can quickly translate into a substantialoverall project cost reduction.Weight spans are another area where traditional assumptions are invalid. It has long been standard practice that wind has no effect on computed weightspans. Sags are calculated with the wind loading, templates are developed with the corresponding sags, and these sags are then applied in the vertical plane.This is simply not the case in a three-dimensional environment. When wind is blowing on a span, the conductor assumes a swung-out catenary. In a levelspan, this swung-out catenary produces a wind and weight span equivalent to that in the vertical plane, so traditional assumptions are correct. In an inclined span, the weight span effect actually shifts and the traditional assumption is no longer valid (See Figure 2).   Re-Engineering The Transmission Line Design Process[8/23/2014 1:41:05 PM] Figure 2  -  A profile and associated three-dimensional view of a line illustrating weight span differences due to wind acting on the wire. All other constantsremain the same.  The exact weight span in this swung out condition on an inclined span is difficult to determine by traditional methods of finding low points in elevationviews, but computers and three-dimensional technology can easily make these determinations. Using the traditional method, weight spans can be insignificant error when considering any wind loaded condition (See Table 1).The software allows the selection of either the traditional method or exact method for calculating effective weight spans when using the wind and weightspan options. It is recommended that the traditional method only be used when comparing PLS-CADD to traditional calculations or on extremely flatterrain. The exact method provides for an accurate three-dimensional line design and should be used on new projects.  Weight Span Weight Span  Weight Span Structure WindSpan w/o Wind w/ Wind  Change Number (m)  (m) (m)  (%) 31 184  146 102 -30% 32 230  287 349 22% 33 190  221 249 13% 34 165  183 199 9%
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