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Lightning Protection of Transmission and Distribution Lines Design Report Project: Dec04-04 Client: Alliant Energy Advisor: Dr. V. Vittal Team Members: Tim Conrad David DieterichSam Muhindo Eric Nelson REPORT DISCLAIMER NOTICE DISCLAIMER: This document was developed as a part of the requirements of an electrical and computer engineering course at Iowa State University, Ames, Iowa. This document does not constitute a professional engineering design or a professional land surveying document. Although the information is intended to be accurate, the associated students, faculty, and Iowa State University make no claims, promises, or guarantees about the accuracy, completeness, quality, or adequacy of the information. The user of this document shall ensure that any such use does not violate any laws with regard to professional licensing and certification requirements. This use includes any work resulting from this student-prepared document that is required to be under the responsible charge of a licensed engineer or surveyor. This document is copyrighted by the students who produced this document and the associated faculty advisors. No part may be reproduced without the written permission of the senior design course coordinator. 4 May 2004 Table of Contents
Definition of Terms iv Introduction 1 Abstract 1 Acknowledgements 1 Problem Statement 1 Operating Environment 2 Intended Users and Uses 2 Assumptions 2 Limitations 3 Expected End Product 3
Design Objectives 5 Functional Requirements 5 Design Constraints 5 Technical Approach Considerations and Results 6 Testing Approach Considerations 7 Recommendations Regarding Project Continuation or Modification 7
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Definition of Terms Arrester: A protective device for limiting surge voltages on equipment by diverting surge current and returning the device to its original status. Conductor: A wire or combination of wires suitable for carrying an electrical current. Conductors may be insulated or bare. Distribution line: Electric power lines which distribute power from a main source substation to consumers, usually at a voltage of 34.5 kV or less. Direct stroke: A lightning stroke direct to any part of a network or electric installation. Flashover: A disruptive discharge through air around or over the surface of solid and liquid insulation, between parts of different potential or polarity, produced by the application of voltage wherein the breakdown path becomes sufficiently ionized to maintain an electrical arc. Insulator: A non-conductive material used on a conductor to separate conducting materials in a circuit. Lightning strike: The complete lightning discharge, most often composed of leaders from a cloud followed by one or more return strokes. Outage: A temporary suspension of operation, especially of electric power. Overhead ground wire (OHGW): Grounded wire or wires placed above phase conductors for the purpose of intercepting direct strokes in order to protect the phase conductors from the direct strokes. Shield wire: Grounded wire(s) placed near the phase conductors for the purpose of protecting phase conductors from direct lightning strokes, reducing induced voltages from external electromagnetic fields, lowering the self-surge impedance of an OHGW system, or raising the mutual surge impedance of an OHGW system to the protected phase conductors. Standard: That which is established by authority as a rule for the measure of quantity, extent, value, or quality. Transmission line: A power line carrying high-voltage electricity between regions. Most transmission lines operate at voltages between 69 and 765 kV. Introduction Abstract In today’s technology-driven society, the need for reliable electric power for thousands of consumer electronic products and sensitive manufacturing processes is growing more today than ever before. Minimizing the effects of lightning strikes to power transmission and distribution lines is a key goal for every utility. Alliant Energy has asked for review and recommendations regarding the ability of their existing transmission and distribution structures to withstand lightning strikes. Using Alliant Energy’s standards and information (such as ground flash density data) gathered from other local utilities and IEEE, the group is attempting to advise the client as to whether or not they are in line with prevailing industry practices. The findings will be summarized for Alliant Energy at the end of the project, in a report on the group’s conclusion. Such findings will provide credibility of Alliant’s practices to their customers. Acknowledgements The following companies and individuals will contribute to the project.
Problem Statement Alliant Energy is seeking to provide as reliable electric service to its customers as is realistically possible. Lightning is a natural threat to power transmission and distribution lines. The line height and exposure makes them exceptionally vulnerable during thunderstorms. Lightning strikes can cause momentary outages and power quality problems. These outages cause disruptions for modern electronic devices such as computers and digital clocks. Like many other utilities, Alliant Energy is looking to minimize momentary outages due to lightning through better line protection design. To help Alliant improve line performance during thunderstorms, the group will research state-of-the-art line design practices and provide the feedback necessary for such improvements. Two forms of protection, arresters and shield wires, help eliminate the effects of direct strokes, flashovers, and shielding failures. Further enhancements can be achieved by improving insulation level and grounding. 
Figure 1 – Typical Shield Wire Configuration Operating Environment The end product of the project is a report summarizing the findings of the group’s research. The end product will be a letter-sized, bound report durable enough to withstand the normal office use associated with multiple reviews and reviewers. Intended Users and Uses Because of confidentiality requirements, Alliant Energy will be the sole user of the end product. Likely primary users include managers and engineers responsible for system planning, design, protection, and reliability activities. Secondary users might include drafters and technicians. The end product will be used for updating and improving Alliant Energy’s standards. It is expected that future decisions regarding line replacement, retrofit, new construction, or upgrades will result from the usage of the group’s end product. The end product is not expected to provide a set of rules regarding performance, but rather a suggested benchmark for system enhancements. Assumptions At the onset of the project, several assumptions had to be made in order to proceed towards accomplishing the necessary objectives. These assumptions may be stated as follows:
Limitations Additionally, several limitations will be encountered. The limitations are as follows:
Expected End Product The end product will be a written report compiling the results of the group’s work. The report will include a study of current design practices by other local utilities. Considerations will include the geometry of the structure such as tower height, conductor spacing, and shield wire placement. Calculation of probabilities or rates (such as flashover rate or its probability) will be incorporated. Protection equipment such as arresters, shield wire, insulators, and structure materials will be discussed in the end product. Additionally, recommendations will be made for any necessary changes to Alliant Energy’s current lightning protection practices. P
Figure 1 - Telescope roposed Approach It is very important to the group that the correct approach is taken to ensure all of the requests of the client are fulfilled. This section presents a list of the group’s necessary components to confirm high probability of project success. It outlines the functional requirements of the end product as well as managing risk and tracking progress throughout the duration of the project. Design Objectives The main objective is to produce a written report compiling the results of the group’s work. The report will include a study of current design practices utilized by other local utilities. Analysis of this data will then be manipulated using a commercial computer software package and compared to Alliant Energy’s current design practices. Lastly, recommendations will be made for any necessary changes to Alliant Energy’s current lightning protection practices. Functional Requirements The proposed project’s main requirement is to provide a recommendation to Alliant Energy regarding lightning protection standards and practices. This conclusion will be met through analysis of other local utilities’ design techniques; however, the group will not disclose any confidential information owned by these utilities to the client. The final recommendations should improve the reliability of service for Alliant Energy’s customers. Design Constraints Foreseeable constraints that affect the group’s end product are as follows:
Figure 2 – Ground Flash Density Map of the United States Technical Approach Considerations and ResultsAlliant Energy will provide the group with access to EPRI’s TFlash program, which will allow the group to examine the lightning performance of different transmission and distribution power line structures. Research will be conducted through IEEE to find structure design standards as well as benchmarks for lightning performance. Design standards from local utilities will also be obtained and studied along with the Alliant Energy and IEEE standards. The results of these studies will determine which structure has the best lightning performance and would be best for Alliant Energy to use. 
Figure 3 –TFlash Application Screenshot If the group is unable to obtain design standards from other utilities, the group will make a recommendation solely on Alliant’s current practices and IEEE standards. The group is optimistic in being able to contact other utilities and obtain design standards. Testing Approach Considerations Because the end product is a report, no testing will be required. Validation of the end product will come from advisor review and client satisfaction with the results rather than from actually performing tests. The final test of the information contained within the end product will come only after implementation of the recommendations by the client. After this, years of data collection are required and such time is well beyond the scope of the project. Recommendations Regarding Project Continuation or Modification The group does not recommend any modifications regarding the direction of the project. The project will be performed as stated in the project plan. Some slight modifications may be implemented if needed. Any and all changes will need to be approved by both the client and the project adviser. Should the course coordinators decide that the project requires or would lend itself nicely to continuation by another senior design team; certain aspects of the project could be expanded. The scope of the project could be extended to include higher voltage level facilities. Specific studies could be performed on Alliant Energy’s existing facilities to examine the performance of designs older than current standards. Detailed Design The group has obtained construction standards for transmission and distribution power lines from Alliant Energy. These designs will be compared to the standards the group has found from IEEE. Construction standards from other local utilities will also be looked at to determine what the most optimal standard is. TFlash will be used to compare these structures with each other.
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Figure 2 – Spiral Galaxy inancial Budget This section will briefly outline the financial budget for the project thus far. As can be seen from the table below, the vast majority of the budget comes in the form of labor. A breakdown of the hours used to calculate labor costs is examined in greater detail in the next section on personal effort. Because labor is not a factor in the project, the only other external costs are those incurred from printing expenses. Table 1 – Original Financial Budget
Table 2 – Revised Financial Budget
Personal Effort Budget This section will outline the current estimates for the personal effort required of each group member. Because the project is highly research intensive, the majority of the time will be focused on such activities. It is also very likely that each group member will end up putting in a very comparable amount of time in most task categories. In the table below, each group member’s contribution is listed. Table 3 – Original Personal Effort Budget
Table 4 – Revised Personal Effort Budget
The changes shown in the tables above reflect the progress of the first semester’s work. Task 1 took more time than anticipated to complete. The group also expects an increase in the amount of time it will require to complete Task 2 (Research and development). A small increase in the amount of time spent on project reporting was also modeled in the table above. Since labor is not included in any of the actual costs for this project, the increase in hours is not a significant deviation from the original plan. Project Schedule This section briefly examines the current schedule for the project. Because exact dates (such as those for class presentation) are not explicitly known, a projected date has been scheduled with flexibility for future rescheduling. While the original schedule has been slightly modified, flexibility was incorporated which will allow the group to stay on track for completion. It should also be noted that the group’s class presentation slot has been moved up to more accurately reflect the presentation time next fall. 
Figure 5 – Original Gantt Chart for Entire Project 
Figure 6 – Revised Gantt Chart for Entire Project Project Team Information This section provides general contact information for the project group members, faculty advisor, and client. Client: Alliant Energy Marlon Vogt 200 First Street Southeast Cedar Rapids, IA 52401 319.786.4399 marlonvogt@alliantenergy.com Faculty advisor: Dr. Vijay Vittal 1126 Coover Ames, Iowa 50011 515.294.8963 vvittal@iastate.edu
Summary
Each year, thousands of brief outages caused by lightning strikes occur on electric transmission and distribution lines across the country. While most of these momentary outages are caused by the operation of protection equipment, even a short interruption in service becomes a nuisance and a source for customer dissatisfaction. To meet an increasing customer demand for highly reliable electric power, Alliant Energy is seeking to validate or improve its current lightning protection practices. The group’s main goal, through various research activities, is to establish a benchmark for good lightning performance of transmission and distribution lines. Alliant’s pursuit of exceptional lightning protection practices will demonstrate their continued commitment to their electric service customers. References Electrical Transmission and Distribution Reference Book, 5th ed., ABB Power T&D Company Inc., Raleigh, North Carolina, 1997. F 
Figure 4 – Earth’s Moon captured by Fick Observatory Telescope The yellow perimeter outlines the equivalent view as seen from the Hubble telescope . alkenberry, L. M., and Coffer, W., Electrical Power Distribution and Transmission, Prentice Hall, Columbus, Ohio, 1996. Fink, D. G., and Beaty, H. W., Standard Handbook for Electrical Engineers, McGraw-Hill, New York, New York, 2000. http://www.epri.com/eprisolutions/lightning/TFlash4%20Features.pdf, April 4, 2004. IEEE Guide for Improving the Lightning Performance of Electric Power Overhead Distribution Lines, IEEE Std 1410-1997. IEEE Guide for Improving the Lightning Performance of Transmission Lines, IEEE Std 1243-1997. Download 130.62 Kb. Share with your friends:
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