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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 Dieterich

Sam 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

Proposed Approach 5

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

Detailed Design 7

Financial Budget 10

Personnel Effort Budget 12

Project Schedule 13

Project Team Information 14

Summary 15

References 16


Figures

Tables


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.


  • Alliant Energy – Marlon Vogt – Provide the group with construction standards, outage data, and most of the financial resources, if required.




  • Iowa State University – Dr. Vijay Vittal – Provide direction, resources, and advice throughout 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:


  • Data is readily available for ground flash density and earth resistivity.




  • Standards from other representative local utilities will be accessible.




  • Recommended system performance criteria will be available from IEEE, Edison Electric Institute, EPRI, or another authority on lightning protection.




  • Calculations will be possible without the assistance of a commercial computer software package.




  • Additional unavailable information can be provided by the client as necessary or suitable alternatives can be established.




  • Financial obligation of the project will be partially funded by team members equally.



Limitations
Additionally, several limitations will be encountered. The limitations are as follows:


  • Alliant Energy would prefer to incur a limited amount of financial resources to complete the end product.




  • Alliant Energy has specified the scope of the project to examine only their line designs for 69 kV and below.




  • The deadline for completion/termination of the project is 17 December 2004.




  • Practices and standards examined should be limited to utilities in the Midwest for geographical and meteorological considerations.




  • The team will not request, nor make available, sensitive information from any utility that would put the company in competitive market disadvantage with other neighboring utilities.




  • The resultant report will be suited for use in the Midwest only.




  • Any proposed or recommended system or facility changes must adhere to all current safety criteria.


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:


  • Limited budget: As with any senior design project, the budget for completion is limited. The group is allotted $150 for expenses, but as the project progresses, the group may encounter the need to purchase data or maps (similar to the ground flash density map shown in Figure 2 below) from outside sources. A software package may also be determined to be helpful in obtaining certain calculations. Any of these expenditures (because they are likely to be more than $150) will need to be approved and funded by the client.




  • Geography: Due to the fact that the group’s client is located over two hours away, it may be difficult to use Alliant Energy’s commercial computer software or obtain other desired data.




  • Time: Success of the project depends heavily on efficient scheduling.




  • Quality of data: Accurate calculations and meaningful correlations are directly related to the quality of the data used. In short, the better the data obtained, the more meaningful the group’s conclusion will be. Therefore, it is important for the group to obtain data from a creditable source, such as Alliant Energy or another local utility, to increase the quality for later calculations.



Figure 2 – Ground Flash Density Map of the United States


Technical Approach Considerations and Results

Alliant 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.
Each type of structure will be modeled using the TFlash software and analysis will be performed to determine which structure will perform the best. The group wishes to see how a single structure will perform alone, as well as a group of multiple structures, perhaps up to twenty miles. This will help determine how the placement of other lightning protection devices affects the performance of a power line.
Other forms of lightning protection besides structure design will be studied. The effect of arresters and shield wires on lightning protection is very important. It should be determined if it will be more beneficial to Alliant Energy to install these devices on existing structures rather than completely replacing the structures with a newer standard.


Figure 4 – Sectional View of a Lightning Arrester
The group will study lightning performance such as flashover rates, ground flash density, and grounding of certain structures. A performance benchmark for this data will be determined either by Alliant Energy or from existing IEEE Standards. Careful analysis will be performed and reviewed to determine the best overall recommendations to be given to Alliant Energy.
A detailed report documenting the group’s findings will be delivered to Alliant Energy. This report will include all calculations performed and structures analyzed. It will include a detailed recommendation of which standard is the best option and supporting evidence why that particular standard is best, and why the other standards were decided against.
Below is a rough outline for the document the group intends to deliver to Alliant Energy at the close of the project:


  1. Introduction

  2. Overview and Summary of Solution Approach

  3. Performance Criteria and Justification

  4. Assumptions and Choice of Variables/Parameters

  5. Simulation/Calculation Results

  6. Simulation/Calculation Breakdown and Interpretation

  7. Proposed Solutions (along with possible “poorer choice” solutions)

  8. Miscellaneous Changes/Proposals/Recommendations

F




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

 

Item

 

Without Labor

With Labor

 

Parts and Materials




 

 




Document Printing

$20

$20

 




Poster Printing

$70

$70

 




Subtotal

$90

$90

 

Labor at $10.00/hr

 

 

 




Conrad, Tim




$1,970

 




Dieterich, David




$1,990

 




Muhindo, Sam




$1,890

 




Nelson, Eric




$2,140

 




Subtotal




$7,990

 

Total

$90

$8,080



Table 2 – Revised Financial Budget

 

Item

 

Without Labor

With Labor

 

Parts and Materials




 

 




Document Printing

$15

$15

 




Poster Printing

$67

$67

 




Subtotal

$82

$82

 

Labor at $10.00/hr

 

 

 




Conrad, Tim




$2,060

 




Dieterich, David




$2,030

 




Muhindo, Sam




$1,830

 




Nelson, Eric




$2,350

 




Subtotal




$8,270

 

Total

$82

$8,352

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

Member

Task 1

Task 2

Task 3

Task 4

Task 5

Member Total

Conrad, Tim

7

100

21

14

55

197

Dieterich, David

7

105

20

17

50

199

Muhindo, Sam

6

95

22

16

50

189

Nelson, Eric

9

110

25

15

55

214

Group Total

29

410

88

62

210

799



Table 4 – Revised Personal Effort Budget

Member

Task 1

Task 2

Task 3

Task 4

Task 5

Member Total

Conrad, Tim

11

100

21

14

60

206

Dieterich, David

13

105

20

17

48

203

Muhindo, Sam

9

95

22

16

41

183

Nelson, Eric

15

125

25

15

55

235

Group Total

48

425

88

62

204

827

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
Team members:


Tim Conrad [Com. Coordinator]

108 Colorado Avenue

Ames, Iowa 50014

563.590.1608

conrad81@iastate.edu
Electrical Engineering


David Dieterich

2316 Frederiksen Court

Ames, Iowa 50010

515.572.7759

mooo452@iastate.edu

Electrical Engineering



Sam Muhindo

246 North Hyland Avenue

Ames, Iowa 50014

773.575.4703

sa6m@iastate.edu

Electrical Engineering



Eric Nelson [Project Leader]

219 South Sherman #6

Ames, Iowa 50010

515.451.3839

esnelson@iastate.edu

Electrical Engineering


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.


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