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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 standardization activities, permission must first be obtained from the Manager, Standards Licensing and Contracts, IEEE Standards Activities Department. Other entities seeking permission to reproduce this document, in whole or in part, must obtain permission from the Manager, Standards Licensing and Contracts, IEEE Standards Activities Department. IEEE Standards Activities Department Standards Licensing and Contracts 445 Hoes Lane, P.O. Box 1331 Piscataway, NJ 08855-1331, USA 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. This is an unapproved IEEE Standards Draft, subject to change. ii 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. iii 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. Copyright © 2005 IEEE. All rights reserved. This is an unapproved IEEE Standards Draft, subject to change. 5 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 Copyright © 2005 IEEE. All rights reserved. This is an unapproved IEEE Standards Draft, subject to change. 6 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. Copyright © 2005 IEEE. All rights reserved. This is an unapproved IEEE Standards Draft, subject to change. 7 October 13, 2005 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 Copyright © 2005 IEEE. All rights reserved. This is an unapproved IEEE Standards Draft, subject to change. 8 October 13, 2005 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. This is an unapproved IEEE Standards Draft, subject to change. 9 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. Copyright © 2005 IEEE. All rights reserved. This is an unapproved IEEE Standards Draft, subject to change. 10 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 Copyright © 2005 IEEE. All rights reserved. This is an unapproved IEEE Standards Draft, subject to change. 11 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. Copyright © 2005 IEEE. All rights reserved. This is an unapproved IEEE Standards Draft, subject to change. 12 October 13, 2005 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