IEEE Std 1243-1997

IEEE Guide for Improving the Lightning Performance of Transmission Lines

Sponsor

Transmission and Distribution Committee of the IEEE Power Engineering Society

Approved 26 June 1997

IEEE Standards Board

Abstract: The effects of routing, structure type, insulation, shielding, and grounding on transmission lines are discussed. The way these transmission-line choices will improve or degrade lightning performance is also provided. An additional section discusses several special methods that may be used to improve lightning performance. Finally, a listing and description of the FLASH program is presented.

Keywords: grounding, lightning protection, overhead electric power transmission, shielding

The Institute of Electrical and Electronics Engineers, Inc. 345 East 47th Street, New York, NY 10017-2394, USA

Copyright © 1997 by the Institute of Electrical and Electronics Engineers, Inc. All rights reserved. Published 1997. Printed in the United States of America.

ISBN 1-55937-937-5

No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher.

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Introduction

(This introduction is not part of IEEE Std 1243-1997, IEEE Guide for Improving the Lightning Performance of Transmission Lines.)

For most overhead power transmission lines, lightning is the primary cause of unscheduled interruptions. Several methods for estimating lightning-outage rates have been developed in the past, and many publications have been written on how to design transmission lines that experience minimum interruptions.

The methods for estimating the lightning performance of transmission lines show several approaches to a reallife engineering problem that is ill-deÞned. Precise constants are rarely known and are often not really constant, input data is difÞcult to describe mathematically except in idealized ways, and outputs may be depictable only by probabilities or average values. By its nature, lightning is difÞcult to study and model. Lightning transients are so fast that air ionization time constants lead to a time- and waveshape-dependent insulation strength. Lightning peak currents may be ten times higher or lower than the median 31 kA value. Typical ground-ßash densities are between 1 and 10 ßashes/km² , so a typical 100 km long strip of width 20 m should receive 2Ð20 ßashes per year. A transmission line of normal height will receive ten times more ßashes because it is tall. Structure footing impedances vary with soil characteristics, ßash current, and time. Nonlinear corona and surge response effects change the waveshape and magnitude of stresses. As a further complication, lightning ßash density varies widely from year to year and changes with location and season.

Any method of judging the lightning performance of transmission lines must cope with these uncertainties. It is pointless, and indeed misleading, to promote a method that is more precise than the accuracy of the input data. The uncertainties of the problem do permit some simpliÞcation of the method; rough estimates are likely to be as correct as a much more detailed solution. It is in this spirit that this guide and the FLASH program have been prepared. If the transmission-line designer keeps these limitations in mind, the factors that most inßuence the lightning performance of a given transmission line may be evaluated.

Knowledge has improved in recent years in such areas as shielding design, stroke characteristics, impulse current behavior of grounds, and lightning ground-ßash density. Work is continuing in these areas, as well as others. However, a simple design guide is needed now. It is the purpose of this publication to provide a simpliÞed guide that includes new advances in this Þeld, for use by transmission-line designers.

The IEEE Working Group on Estimating the Lightning Performance of Overhead Transmission Lines had the following membership during the preparation of this guide:

James T. Whitehead, Chair, 1985-1989 William A. Chisholm, Chair, 1989-1997

John G. Anderson Christopher Hickman Hideki Motoyama John W. Anderson Andrew R. Hileman Charles H. Moser Philip Barker Atsuyuki Inoue Abdul M. Mousa Ralph Bernstein Marasu Ishii Richard E. Orville James E. Chapman Wasyl Janischewskyj Dee E. Parrish Pritindra Chowdhuri John Kappenman Charles Pencinger Ernico Cinieri Robert C. Latham John B. Posey Roger Clayton Duilio M. Leite Joseph D. Renowden Luigi Dellera Vito J. Longo Farouk A. M. Rizk Hamid Elahi Harry G. Mathews Thomas Short Andrew J. Eriksson James McBride Mohamed H. Shwehdi George Gela Thomas McDermott Martin A. Uman Stanislaw Grzybowski Edward R. Whitehead

The Working Group would like to thank the many individuals who reviewed the text and provided comments in the review and balloting process.

iii

Copyright © 1997 IEEE. All rights reserved.

This document is dedicated to the work and memory of Ed Whitehead:

ÒLightning is the enemy, Trees are your friends, TheyÕll shield your lines HoweÕer the leader bends.Ó

The following persons were on the balloting committee:

Hanna E. Abdallah Atsuyuki Inoue Percy E. Pool Edward J. Adolphson Wasyl Janischewskyj Steven C. Powell Glenn Andersen John G. Kappenman Patrick D. Quinn J. G. Anderson Richard Kennon Parvez Rashid James E. Applequist Jeff J. Kester Jerry L. Reding Edwin Averill Robert O. Kluge Joseph Renowden Michael P. Baldwin Ed Knapp Frank Richens Phil P. Barker Nestor Kolcio Stephen J. Rodick Ron L. Barker Alan E. Kollar John R. Rossetti E. Betancourt Donald E. Koonce G. W. Rowe John Boyle David J. Koury Tim E. Royster H. Steve Brewer Samy G. Krishnasamy Thomas J. Rozek Joseph F. Buch Barin Kumar John S. Rumble James J. Burke Stephen R. Lambert Anne-Marie Sahazizian Vernon L. Chartier Robert C. Latham Mahesh P. Sampat Nisar Chaurdhry Benny H. Lee Donald Sandell Prit Chowdhuri Gerald E. Lee Neil P. Schmidt Don Chu Antonio L. Lim John Schneider Enrico Cinieri Joseph Ma Minesh Shah Sam Cluts K. T. Massouda Devki N. Sharma Thomas M. Compton Mike. McCafferty John Shea F. Leonard Consalvo John McDaniel Tom Short William T. Croker Nigel P. McQuin Mohamed H. Shwehdi Paul L. Dandeno Ross McTaggart Hyeong Jin Sim Glenn A. Davidson John E. Merando Jr. Pritpal Singh R. Decker Sam Michael Tarkeshwar Singh Tom. Diamantis J. David Mitchell Robert A. Smith William K. Dick Daleep Mohla Stephen F. Smith Dale A. Douglass Richard K. Moore Brian T. Steinbrecher Robert Engelken J. H. Moran Gary E. Stemler William E. Feero Hideki Motoyama L .R. Stensland Jon M. Ferguson Abdul M. Mousa Robert P. Stewart Harald Fien Jay L. Nicholls Mike F. Stringfellow James Funke D. L. Nickel Andy Sweetana George Gela George B. Niles Eva J. Tarasiewicz Donald A. Gillies Stig L. Nilsson Subhash C. Tuli Edwin J. Tip Goodwin Ronald J. Oedemann J. G. Tzimorangas I. S. Grant Robert G. Oswald Joseph J. Vaschak Stan Grzybowski Gerald A. Paiva John Vithayathil Adel E. Hammad Bert Parsons Reigh Walling Jerome G. Hanson Mohammad A. Pasha Daniel J. Ward Donald G. Heald Jesse M. Patton James T. Whitehead Roland Heinrichs David F. Peelo Jeffrey S. Williams Richard W. Hensel Carlos Peixoto Frank S. Young Steven P. Hensley Thomas J. Pekarek Luciano E. Zaffanella Christopher W. Hickman Robert C. Peters Peter Zhao Andrew Robert Hileman Trevor Pfaff Rich Zinser John Hunt R. Leon Plaster William B. Zollars

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Copyright © 1997 IEEE. All rights reserved.

When the IEEE Standards Board approved this guide on 26 June 1997, it had the following membership:

Donald C. Loughry,Chair	Richard J. H Andrew G. Salem, Secretary	olleman, Vice Chair
Clyde R. Camp	Lowell Johnson	Louis-Fran•ois Pau
Stephen L. Diamond	Robert Kennelly	Gerald H. Peterson
Harold E. Epstein	E. G. ÒAlÓ Kiener	John W. Pope
Donald C. Fleckenstein	Joseph L. KoepÞnger*	Jose R. Ramos
Jay Forster*	Stephen R. Lambert	Ronald H. Reimer
Thomas F. Garrity	Lawrence V. McCall	Ingo RŸsch
Donald N. Heirman	L. Bruce McClung	John S. Ryan
Jim Isaak	Marco W. Migliaro	Chee Kiow Tan
Ben C. Johnson		Howard L. Wolfman

*Member Emeritus

Also included are the following nonvoting IEEE Standards Board liaisons:

Satish K. Aggarwal

Alan H. Cookson

Erika H. Murphy IEEE Standards Project Editor

National Electrical Safety Code and NESC are registered trademarks and service marks of the Institute of Electrical and Electronics Engineers, Inc. Windows is a trademark of Microsoft Corporation.

Copyright © 1997 IEEE. All rights reserved.

v

Contents

1.	Overview.............................................................................................................................................. 1
	1.1 Scope............................................................................................................................................ 1
	1.2 Purpose......................................................................................................................................... 1
	1.3 Disclaimer.................................................................................................................................... 2
2.	References............................................................................................................................................ 2
3.	Definitions and Acronyms................................................................................................................... 2
	3.1 Definitions.................................................................................................................................... 2
	3.2 Acronyms..................................................................................................................................... 4
4.	Route selection..................................................................................................................................... 4
	4.1 Lightning frequency of incidence................................................................................................ 4
	4.2 Route effects ................................................................................................................................ 5
	4.3 Structure height............................................................................................................................ 5
	4.4 Soil resistivity .............................................................................................................................. 6
	4.5 Adjacent environment.................................................................................................................. 6
5.	Shielding .............................................................................................................................................. 6
	5.1 Shielding angle............................................................................................................................. 7
	5.2 The final leader step..................................................................................................................... 7
	5.3 Flashover from shielding failure.................................................................................................. 9
	5.4 Shielding and engineering.......................................................................................................... 10
	5.5 Shielding of the center phase..................................................................................................... 12
	5.6 Overhead ground wire size and operating losses....................................................................... 12
6.	Insulation............................................................................................................................................ 13
	6.1 Effect of voltage waveshapes..................................................................................................... 13
	6.2 Effect of insulation levels and insulation type........................................................................... 16
	6.3 Wood or fiberglass in series with insulators.............................................................................. 17
	6.4 Effect of power-line voltage ...................................................................................................... 17
7.	Tower footing impedance .................................................................................................................. 18
	7.1 Composite line performance...................................................................................................... 18
	7.2 Supplemental grounding............................................................................................................ 19
	7.3 Counterpoise .............................................................................................................................. 20
	7.4 Resistance of complex footings ................................................................................................. 21
	7.5 Special grounding effects........................................................................................................... 21

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Copyright © 1997 IEEE. All rights reserved.

8.	Special methods of improving lightning performance....................................................................... 22
	8.1 Additional shield wires .............................................................................................................. 22
	8.2 Guy wires on transmission towers............................................................................................. 23
	8.3 Ground wire on separate structures............................................................................................ 23
	8.4 Line surge arresters.................................................................................................................... 23
	8.5 Unbalanced insulation on double-circuit lines........................................................................... 24
	8.6 Active air terminals.................................................................................................................... 24
Annex	A (informative) Isolated bonding of wooden structures .................................................................... 26
Annex	B (normative) The FLASH program.................................................................................................. 27
Annex	C (informative) Bibliography............................................................................................................. 34

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Copyright © 1997 IEEE. All rights reserved.

IEEE Guide for Improving the Lightning Performance of Transmission Lines

1. Overview

1.1 Scope

For this guide, a transmission line is any overhead line with a phase-to-phase voltage exceeding 69 kV and an average conductor height of more than 10 m. The transmission line is usually shielded by one or more overhead ground wires (OHGWs), at least for a short distance from a substation. While reference is primarily made to ac transmission characteristics, the guide is also relevant for high-voltage direct-current (HVDC) overhead lines.

The guide is written for the transmission-line designer. When given the problem of designing or redesigning a transmission line, the designer should consider certain limiting factors such as the voltage level, the beginning and ending points for the transmission line, and the desired ampacity of the line. Sometimes the exact route, and the type of conductor and structure have already been determined. Usually the designer may choose structural details, the geometry of the structure, the structure height, the exact placement of the OHGWs, the amount and type of insulation, the type of grounding, and other design features of a line. This guide is written to show the designer which choices will improve or degrade lightning performance. Sections of the guide discuss the effect of routing, structure type, insulation, shielding, and grounding. An additional section discusses several special methods, which may be used to improve lightning performance. Finally, in Annex B, a listing and description of the FLASH program is presented.

The line designer should be aware that lightning performance is not of primary importance in the economics of line designing. Other factors, such as line length, right-of-way costs, construction costs, material costs, and losses affect the economics of a line design much more than lightning performance. The designer should always balance the costs of higher insulation levels, improved grounding, better shielding, or line relocation against the beneÞts of improved reliability.

1.2 Purpose

This guide contains simple mathematical equations, tables, and graphs that provide the information needed to design an overhead power transmission line with minimum lightning interruptions. Versions 1.6 and 1.7 of the FLASH program are provided on the diskette included with this guide. Annex B includes a description of the program. The FLASH program uses the models in the design guide along with a description of transmissionline features to estimate the lightning outage rate that may be expected. These simpliÞed models may also be adapted to assess the beneÞts of novel methods for improving lightning performance.

1

Copyright © 1997 IEEE. All rights reserved.

IEEE Std 1243-1997

IEEE GUIDE FOR IMPROVING THE

1.3 Disclaimer

The FLASH program is included in this guide as a convenience to the user. Other numerical methods may be more appropriate in certain situations. The IEEE Working Group on Estimating the Lightning Performance of Overhead Transmission Lines of the Lightning and Insulator Subcommittee has made every effort to ensure that the program yields representative calculations under anticipated conditions. However, there may well be certain calculations for which the method is not appropriate. It is the responsibility of the user to check calculations against Þeld experience or other existing calculation methods.

2. References

This guide shall be used in conjunction with the following standards. When the following standards are superseded by an approved revision, the revision shall apply.

ANSI C2-1997, National Electrical Safety Code^¨ (NESC^¨ ).¹

ANSI C29.1-1988 (Reaff 1996), American National Standard for Electric Power InsulatorsÑTest Methods.²

ANSI C29.2-1992, American National Standard for InsulatorsÑWet Process Porcelain and Toughened GlassÑSuspension Type.

ANSI C29.8-1985 (Reaff 1995), American National Standard for Wet-Process Porcelain Insulators (Apparatus, Cap, and Pin Type).

3. DeÞnitions and Acronyms

3.1 DeÞnitions

3.1.1 active air terminal: An air terminal which has been modiÞed to lower its corona inception gradient.

3.1.2 air terminal (lightning protection): The combination of an elevation rod and brace, or footing placed on upper portions of structures, together with tip or point, if used.

3.1.3 back ßashover (lightning): A ßashover of insulation resulting from a lightning stroke to part of a network or electric installation which is normally at ground potential. See also: direct-stroke protection.

3.1.4 back-ßashover rate: The annual outage rate on a circuit or tower-line length basis caused by back ßashover on a transmission line.

3.1.5 counterpoise: A conductor or system of conductors arranged beneath the line; located on, above, or most frequently below the surface of the earth; and connected to the grounding systems of the towers or poles supporting the transmission lines.

3.1.6 critical current: The Þrst-stroke lightning current to a phase conductor which produces a critical impulse ßashover voltage wave.

1The NESC is available from the Sales Department, American National Standards Institute, 11 West 42nd Street, 13th Floor, New York, NY 10036, USA. It is also available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, P.O. Box 1331, Piscataway, NJ 08855-1331, USA.

2ANSI publications are available from the Sales Department, American National Standards Institute, 11 West 42nd Street, 13th Floor, New York, NY 10036, USA.

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Copyright © 1997 IEEE. All rights reserved.