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IEEE P1627/D1.1
Date: October 13, 2005
Draft Standard for DC Electrification Overhead
Contact Systems, Including Application of
Lightning Arresters for Transit Systems
Prepared by Working Group 17 of the Overhead Contact System Subcommittee
Sponsored by the Rail Vehicle Transit Interface Standards Committee
of the
IEEE Vehicular Technology Society
Copyright © 2005 by the Institute of Electrical and Electronics Engineers, Inc.
Three Park Avenue
New York, New York 10016-5997, USA
All rights reserved.
All rights reserved. This document is an unapproved draft of a proposed IEEE Standard. As such, this
document is subject to change. USE AT YOUR OWN RISK! Because this is an unapproved draft, this
document must not be utilized for any conformance/compliance purposes. Permission is hereby granted for
IEEE Standards Committee participants to reproduce this document for purposes of IEEE standardization
activities only. Prior to submitting this document to another standards development organization for
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Contracts, IEEE Standards Activities Department. Other entities seeking permission to reproduce this
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October 13, 2005
IEEE P1927/D1.1
Introduction
(This introduction is not part of IEEE P1627/D1.1, Draft Standard for DC Electrification Overhead Contact
Systems, Including Application of Lightning Arresters for Transit Systems.)
The majority of the present operating dc electrified rail systems use OCS or third rail to supply power to the
vehicles. OCS is potential candidates of lightning strikes.
Basic lightning protection could be grouped into the following subsystems:

Direct stroke diverters such as lightning rods and ground wires. The purpose of these subsystems
is to intercept lightning strokes and discharge them to ground.

Low grounding resistance (lightning rods, pole footings and lightning arrester ground) to hold
structure potential bellow insulation flashover and breakdown level.

Lightning arrester application to reduce power circuit surge voltage below insulation flashover and
breakdown of the equipment.

Set insulation levels to minimize outages due to lightning.
The working group’s approach for developing the OCS lightning protection standard will focus on the first
three of the above mentioned subsystem. Setting basic insulation levels for the OCS is part of the scope of
work of another subcommittee. The electric utility industry universally recognizes that long transmission
lines must insulate against lightning rather than merely for the operating voltage if they are to provide
acceptable service from the standpoint of minimizing the lightning outages. Although, the setting of
insulation levels for OCS is not part of the scope of this standard, we would like to recommend that similar
to the utility transmission line OCS insulation standards subcommittee should consider other factors such as
lightning outages and contamination prior to selecting insulation levels.
The other feature that makes OCS designers and engineers contemplate is the question as to whether to
shield nor not to shield the OCS system with overhead ground wire(s). A lightning stroke terminating on an
unshielded OCS will encounter surge impedance much higher than that of a ground wire shielded OCS. As
a result of the higher surge impedance, the induced voltage will be higher and consequently the number of
flashovers across the OCS insulators will be higher. While the above discussion brings out much inferior
performance per circuit mile for unshielded rather than shielded OCS, the unshielded OCS can be
acceptable in regions of very low isokeraunic levels and urban areas where shielding may be provided by
trees and nearly building. Also, it should be mentioned that strokes to unshielded OCS will set up traveling
waves on OCS conductors that will travel to the substation. Thus the substation is the recipient of large and
more numerous lightning surges from unshielded OCS than from shielded OCS. Please also keep in mind
that the crest value of the surge will be determined by the insulation level of the OCS.
While we are evaluating the risk to the OCS from direct strokes, we must not overlook the effect of induced
lightning strokes, especially OCS located near transmission lines and other shielding structures.
Shielded OCS with ground wires in addition to having much smaller surge impedance and consequently
reduced crest voltages, lightning strokes progressively drain into the ground as the waves successfully reach
adjacent towers and in a few spans from the struck pole the waves disappear. This establishes the other
advantage of the shielded OCS that the equipment in the substation are not subjected to surges for lightning
strokes on the OCS a few spans away from the substation.
Copyright © 2005 IEEE. All rights reserved.
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October 13, 2005
IEEE P1927/D1.1
Fig. 1
2002 Edition
This edition of IEEE P1627, Standard for Grounding Practice for DC Electrification Overhead Contact
System, Including Application of Lightning Arresters for Transit Systems was prepared by the
VEHICULAR TECHNOLOGY SOCIETY, Rail Transit Vehicle Interface Standards Committee, Overhead
Contact Systems Sub-Committee for Rail Transit, power supply working group.
Origin and Development of IEEE P1627
The Overhead Contact Systems Sub-Committee for Rail Transit Systems was formed in 2001 with the
purpose of developing standards governing the design and construction of overhead contact systems (OCS)
for rail transit. The primary concern of the committee regarding OCS for light rail systems was the lack of
uniform practices for grounding OCS and application of lightning arresters and their effect on safety to
passengers, personnel and equipment, and reliability and cost effectiveness of such systems.
Prior and during the development of this standard there were reports of lightning arrester failures in several
systems resulting in service interruption and equipment failures. Questions were being raised regarding the
grounding of OCS support poles and the pros and cons of using lightning arresters in the OCS. Most
importantly, there was no understanding of the lightning arrester failures and recommended application
guidelines. The good news so far has been that there have been no reports regarding personnel injuries.
At the time this standard was completed, the working group had the following membership:
Nikitas D. Rassias, Chair
Ramesh Dhingra, Co-Chair
Alan Blatcxhford
Butch Campbell
Ron Clark
Ian Hayes
Albert Hoe
Michael Long
Steve Mitan
Jay Sender
Jeffrey N. Sisson
Benjamin Stell
Gary Touryan
Carl Wessel
Paul White
Tom Yong
The following members of the balloting committee voted on this standard. Balloters may have voted for
approval, disapproval, or abstention. (To be provided by IEEE editor at time of publication.)
_____________________________________________________________________________________
Copyright © 2005 IEEE. All rights reserved.
This is an unapproved IEEE Standards Draft, subject to change.
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October 13, 2005
IEEE P1927/D1.1
Contents
Introduction .................................................................................................................................................... ii
1. Overview ..................................................................................................................................................... 5
1.1 Scope ..................................................................................................................................................... 5
1.2 Purpose .................................................................................................................................................. 5
2. References ................................................................................................................................................... 6
3. Definitions, abbreviations, and acronyms .................................................................................................... 7
3.1 Definitions ............................................................................................................................................. 7
3.2 Abbreviations and Acronyms ................................................................................................................ 8
4. Grounding .................................................................................................................................................... 9
4.1 Ground Wire. ......................................................................................................................................... 9
4.2 OCS support grounding ......................................................................................................................... 9
5. Lightning Arresters ...................................................................................................................................... 9
5.1 Application ............................................................................................................................................ 9
5.2 Lightning Arrester Rating .................................................................................................................... 10
6. Service Requirements ................................................................................................................................ 11
7. Testing ....................................................................................................................................................... 11
7.1 Design Test .......................................................................................................................................... 11
7.2 In Service Test ..................................................................................................................................... 12
Bibliography .............................................................................................................................................. 13
Copyright © 2005 IEEE. All rights reserved.
This is an unapproved IEEE Standards Draft, subject to change.
iv
October 13, 2005
IEEE P1927/D1.1
Draft Standard for DC Electrification Overhead
Contact Systems, Including Application of
Lightning Arresters for Transit Systems
1. Overview
1.1 Scope
The scope of this standard covers practices for grounding OCS used in dc traction electrification for rail,
light rail, and trolley bus, including the proper application and testing of lightning arresters.This style sheet
is intended to provide IEEE standards working groups with guidelines for the formatting of draft standards
that are to be submitted to the IEEE Standards for publication and inclusion in the IEEE Standards
document database.
1.2 Purpose
The purpose of this standard is to establish minimum requirements for grounding of OCS and application of
lightning arresters that will provide a reasonable degree of safety to personnel and equipment from lightning
and its related hazards. At present time there are no uniform practices for grounding OCS used in dc
traction electrification or for application of lightning arresters. Such a standard will provide increased
protection to passengers, personnel and equipment, reduce maintenance and initial costs and improve
systems performance.
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October 13, 2005
IEEE P1927/D1.1
2. References
This standard shall be used in conjunction with the following publications. If the following standards are
superceded by an approved version, the latest revision shall apply. In case of conflict between this standard
and the referenced document, this standard shall take precedence. Those provisions of the referenced
standard that are not in conflict with this standard shall apply as referenced.
National Electrical Safety Code
National Electrical Code
Canadian Electrical Code
Canadian Standards Association
British Standard BSN EN 50124-1:2001 Railway Applications – Insulation coordination
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October 13, 2005
IEEE P1927/D1.1
3. Definitions, abbreviations, and acronyms
3.1 Definitions
Clearance: Shortest distance in air between two conductive materials
Creepage Distance: Shortest distance along the surface of the insulating material between two conductive
materials
Electrical Section: Part of an electrical circuit having its own voltage rating for insulation coordination
Grounded: electrical section connected to earth that cannot be interrupted
Ground Wire: The conductor installed for the purpose of providing electrical continuity between the
supporting structure of the overhead contact system and the common return or grounding system.
Insulated: All components isolated from the energized OCS conductors by at least one level of insulation.
An insulated section may be under the influence of adjacent energized circuits. An insulated section may be
considered as an electrical section.
Lightning Arrester: A device typically mounted on OCS poles and connected to the OCS, designed to
protect insulated feeder cables against lightning, by providing a path to ground through a spark-gap, with or
without variable resistance elements.
Nominal voltage: Value assigned to a circuit or system approximately equilivent to the working voltage for
designating the voltage class.
Overvoltage: Voltage having a peak value exceeding the maximum steady state voltage at normal
operating conditions.
Rated Voltage: Value of voltage assigned to a component, device or equipment
Rated Impulse Voltage: Value of voltage assigned to the equipment referring to the specified withstand
capability of the insulation against transient overvoltages.
Rated Insulation Voltage: RMS withstand voltage assigned to the equipment referring to the specified
permanent (over five minutes) withstand capability of the insulation between energized components and
earth.
Surge Arrester: See Lightning Arrester
Working Voltage: Highest RMS value of the ac or dc voltage, which can occur between two points across
any insulation when each electrical circuit is at maximum voltage.
Working Peak Voltage: Highest value of the voltage which can occur in service across any particular
insulation.
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IEEE P1927/D1.1
3.2 Abbreviations and Acronyms
ANSI
AREMA
ASTM
AWG
DC
FRA
IEEE
ISO
LRV
NEC
NEMA
NESC
NETA
NFPA
OCS
OSHA
RMS
ROW
TES
UBC
UL
USASI
USDOT
American National Standards Institute
American Railway Engineering Association
American Society for Testing and Materials
American Wire Gauge
Direct Current
Federal Railroad Administration
Institute of Electrical and Electronics Engineers
International Organization for Standards
Light Rail Vehicle
National Electrical Code (NFPA-70)
National Electrical Manufacturers Association
National Electrical Safety Code
National Electrical Testing Association
National Fire Protection Association
Overhead Contact System
Occupational Safety and Health Administration Act
Root Mean Square
Right-of-way
Traction Electrification System
Uniform Building Code
Underwriters Laboratories, Inc.
United States of America Standards Institute
United States Department of Transportation
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IEEE P1927/D1.1
4. Grounding
4.1 Ground Wire.
4.1.1 OCS, when installed in regions where the isokeraunic level is higher than 10, shall be protected from
lightning surges with an overhead ground wire or wires as required to maintain a maximum shielding angle
of no more than 45 degrees Fig. 1.
4.1.2 Ground wire shall be 9/16 diameter Copperweld having 19 number 9 conductors, and 40%
conductivity. Hard drawn copper wire 4/0 Awg stranded could also be used if theft is not a concern.
4.1.3 Ground wire shall be bonded at each OCS support with a 9/16 Copperweld, 40% conductivity wire.
4.1.4 Ground wires shall be terminated into the traction power substations and shall be connected to the
substation ground grid.
4.2 OCS support grounding
4.2.1 OCS support poles with lightening arresters attached to them shall have 5 ohms footing resistance
maximum. OCS poles without lightning arresters attached to them hall have 25 ohms footing resistance
maximum. The grounding of the pole could be accomplished by connecting the pole foundation steel
caisson to the pole, by providing ground rods or counterpoise wires. Earth resistivity shall be measured and
the measurements shall be used to calculate the pole footing resistance. Following the installation of the
pole, the footing resistance shall be measured and recorded for future reference.
4.2.2 Overhead ground wire shall also be sized to carry load and fault current for electrical services attached
to the pole including traction power.
4.2.3 Where multiple ground rods are being used, they shall be spaced apart further than the length or their
immersion. Two 10-foot rods should be spaced 20 feet apart. Connect ground rods to grounding wire with
4/0 Awg copper wire located 18 inches below ground. Provide two bonds from the 4/0 Awg grounding
wire to the pole. Use -corrosive connections to connect the grounding conductor to the ground rods and to
the pole.
5. Lightning Arresters
5.1 Application
5.1.1 Lightning arresters shall be provided and shall be connected to the OCS at mid point between
substations and at places where electrical equipment are connected to the OCS, such as insulated cables,
transformers, and circuit breakers. For OCS systems that require multiple taps from parallel underground
feeders, lightning arresters shall be and shall be connected to the OCS system at 1000 feet maximum
spacing. Also, lightning arresters shall be connected to the catenary system at places where tight electrical
clearances exist between the OCS and overpasses such as bridges, convention centers or tunnels.
5.1.2 Use a 9/16 Copperweld 600 insulated with jacket wire 40% conductivity to connect the lightning
arrester to the OCS support footing ground grid using an exothermic weld. If theft is not a concern than
copper wire of equivalent size can be substituted for the copperweld ground wire. Maintain lightning
arrester ground leads to a minimum. If is not practical to connect the lightning arrester to the catenary pole
Copyright © 2005 IEEE. All rights reserved.
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October 13, 2005
IEEE P1927/D1.1
(round pole) then extend the ground wire down the OCS support and connect it to the OCS support’s
ground grid (use insulated grounding conductor to avoid arcing).
5.1.3 Locate lightning arresters directly (as close as possible) at the terminals of the apparatus being
protected. At this location, and with the arrester ground leads connected directly to the tank, frame, or other
metallic structure which supports the insulated parts, the voltage applied to the insulation will be limited to
the sparkover voltage and the discharge of the arrester.

Name Plate Information

The following information shall be provided:

Suitable for application on DC traction systems

Rated voltage

Nominal discharge current

Pressure relief capability in KA

Manufacturers name

Year of manufacture

Serial number
5.2 Lightning Arrester Rating
5.2.1 Lightning arresters discharge voltage is no more than 80% of the BIL of the equipment that is
protecting.
5.2.2 Voltage rating of lightning arresters shall be 125% of maximum continuous system operating voltage
measured from phase OCS to rail or the voltage rating of the lightning arrester shall be at least 5% above
the momentary maximum possible system operating voltage under any normal or expected peak fault
condition (allowing 5% for utility overvoltage and a percent for regeneration based no system parameters).
OCS to rail voltage shall not exceed the rating of the lightning arrester under all traction and utility systems
operating conditions.
Table 1 Traction Power Voltage Levels
System Nominal Voltage
(Volts)
System Maximum
Continuous Voltage (Volts)
System Maximum Momentary
Voltage (Volts)
Up to 850
1020
1,150
1,500
1,800
2,000
3,000
3,600
4,000
5.2.3 Lighting arrester rating shall be as listed on table 1.
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October 13, 2005
IEEE P1927/D1.1
Table 1- Arrester Ratings
Lightning Arresters
System Maximum
Temporary
Voltage Volts DC
Minimum Rated
Voltage Volts
DC
Nominal
Discharge
Current KA
Pressure Relief
Capacity KA
Maximum residual Voltage
at 20 KA Discharge current
in KV
1,150
1,300
100
20
5
2,000
2,100
100
20
9
4,000
4,200
100
20
16
Lightning Arresters
BIL KV
Minimum Rated
Voltage Volts DC
DC Withstand Minimum
Dry KV
Wet KV
Minimum
Energy KJ
1,300
65
45
25
3.22
2,100
65
45
25
4.83
4,200
65
45
25
11.27
6. Service Requirements
Operating ambient temperature shall be between -40 degrees C and + 40 degrees C. Altitude shall not
exceed 1800 feet. System OCS to ground voltage shall be within the rating of the arrester under all system
operating conditions.
7. Testing
7.1 Design Test

Lighting arrester shall be subjected to the following design test:

Insulation withstand test

DC Dry and Wet spark over test

Discharge voltage test

Impulse protective level voltage time characteristics
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October 13, 2005
IEEE P1927/D1.1

Accelerated aging procedure

Pressure relief test
New and clean arresters shall be used for each design test.
The arrester shall be mounted in the position(s) in which it is designed to be used.
Ambient temperature for test shall be -10 degrees centigrade to +20 degrees centigrade
more then + or – 3 degrees centigrade.
and shall not very
7.2 In Service Test
Lightning arresters shall be tested within a period of five (5) years. The yearly sampling for testing shall be
a group of twenty percent of all of the arrestors for a given line.
A representative sample on the in-service arrestors and on-hand spares shall be tested for possible
degradation and failure. Based on the testing results found either further samples maybe required for testing
period, or no further testing will be required until the next year, or identified testing period. The time
interval between testing the entire inventory shall be a maximum of five years, from the in-service date of
the alignment or line.
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IEEE P1927/D1.1
Bibliography
Lightning Strikes
British Standard BSN EN 50124-1:2001 Railway Applications – Insulation coordination
Copyright © 2005 IEEE. All rights reserved.
This is an unapproved IEEE Standards Draft, subject to change.
13