Engineering Standard Electrical MEST 000002-07 Earthing Requirements for Transmission Structures Version: 1 Issued: February 2015 Owner: Engineering Approved By: Patrick Kelly Head of Electrical Engineering Authorise For Use By: Paul O Halloran Chief Engineer PRINTOUT MAY NOT BE UP-TO-DATE; REFER TO METRO INTRANET FOR THE LATEST VERSION
Approval Amendment Record Approval Date Version Description 20/02/2015 1 Initial issue PRINTOUT MAY NOT BE UP-TO-DATE; REFER TO METRO INTRANET FOR THE LATEST VERSION Page 2 of 7
Table of Contents 1 Purpose... 4 2 Scope... 4 3 Abbreviation... 4 4 Definitions... 4 5 References & Legislations... 5 5.1 General... 5 5.2 MTM Standards/Documents... 5 5.3 Rail Industry Standards/Documents... 5 5.4 Australian Standards/Documents... 5 5.5 International Standards/Documents... 5 6 Related Documents... 5 7 Basis of this Standard... 6 8 Risk... 6 9 Technical... 6 10 Appendices... 7 PRINTOUT MAY NOT BE UP-TO-DATE; REFER TO METRO INTRANET FOR THE LATEST VERSION Page 3 of 7
1 Purpose To define the requirements for the earthing of overhead structures supporting AC transmission. 2 Scope This Standard applies to all metallic and concrete structures supporting the transmission lines on the metropolitan railway network. This includes standalone transmission masts and shared structures. Should a transmission system on poles at 650V AC or higher phase to phase voltage be introduced, the provisions of this Standard shall apply. It does not apply to timber poles supporting AC transmission or 1500V traction conductors or to poles supporting cables at a potential of 415V or lower. The earthing of structures supporting AC transmission operating switches shall be specifically designed and constructed to provide step and touch potentials in accordance with ENA EG1-2006 Chapter 7. This standard does not apply to the earthing of substations or other buildings. 3 Abbreviation AC DC Alternating Current Direct Current High Voltage 4 Definitions Earthing AC Transmission Shall Shared Structure Should Standard Step and Touch Potential The installation of electrodes and connections to structures to maintain the structure near earth potential under a fault condition For the purpose of this standard, AC transmission is AC power equal to or greater than 650V phase to phase. Is used as the descriptive word to express a requirement that is mandatory to achieve conformance to the standard. An overhead structure which contains AC transmission and either or both signals and 1500V traction wiring Is used as the descriptive word to express a requirement that is recommended in order to achieve compliance to the standard. Should can also be used if a requirement is a design goal but not a mandatory requirement. A set of high level requirements that are mandatory to be adhered to achieve MTM s objectives. The voltage that a person may be exposed to under fault condition at a location PRINTOUT MAY NOT BE UP-TO-DATE; REFER TO METRO INTRANET FOR THE LATEST VERSION Page 4 of 7
5 References & Legislations 5.1 General 5.2 MTM Standards/Documents L1-NAM-INS-005 MEST 000002-02 F7748 STD_E0144 Design Practice Note - 22kV Support Structures Electrical Networks Standard - Overhead Line Electrification Earthing Arrangement Transmission Switch Structure Transmission Structure Earthing 5.3 Rail Industry Standards/Documents IPGOR-01 ENA EG1-2006 Chapter 7 PTC Train Infrastructure Electrical Safety Rules (High Voltage Rules) Substations Earthing Guide Power Frequency Voltage Design 5.4 Australian Standards/Documents AS/NZS 3000 AS/NZS 3000:2007 Appendix K Wiring Rules High Voltage Electrical Installations (as applicable in Victoria) 5.5 International Standards/Documents 6 Related Documents NA PRINTOUT MAY NOT BE UP-TO-DATE; REFER TO METRO INTRANET FOR THE LATEST VERSION Page 5 of 7
7 Basis of this Standard This Standard is based on Schedule K of the Wiring Regulations, AS 3000 and research of practices by other 1500V DC railways. It is to be noted that the current version of AS 3000 does not have Schedule K incorporated but that the Schedule is specified by Energy Safe Victoria as being applicable. The maximum permissible earth electrode resistance for the high voltage installation is 30 ohms. Separately, in locations accessible to persons, the conditions under fault condition must be examined to ensure that step and touch potentials are not exceeded. Step and touch potentials shall comply with the requirements of ENA EG1-2006 Chapter 7. Where structures supporting AC transmission are in public accessible areas, the design of the earthing arrangement shall be developed by MTM Engineering. It is to be especially noted where the AC transmission supporting structure is within 2000mm of other metallic structures, the design of the earthing shall ensure step and touch potentials are in accordance of the requirements of ENA-EG1 Chapter 4. The design shall record the presence of the adjacent metallic structures and how step and touch potentials are addressed. 8 Risk The earthing of structures is based on the risk presented to persons and assets. The original installation of the railway electrification did not address earthing on non-switching structures except to rely on the structures being bonded to power rail through a spark gap. The resistance to earth was assumed to be reasonable with the length of rail attached to the spark gap. A consequence of a transmission fault without the proper earthing is damage to the track circuits, disruption to services and possible injury to persons. 9 Technical Table 1 sets the earthing requirements for structures with transmission on the railway. Where there is uncertainty of the target electrode resistance at a specific location, all queries shall be directed to the Head of Engineering, Electrical for clarification. PRINTOUT MAY NOT BE UP-TO-DATE; REFER TO METRO INTRANET FOR THE LATEST VERSION Page 6 of 7
Table 1 - Transmission Structure Earthing Structure Configuration Transmission, 1500V and no signals Or Standalone Transmission mast Transmission, signals and 1500V Location Rail corridor where persons may approach structure but not normally accessible Station area - platforms, car parks and within 10m of pedestrian areas, not fenced Target Electrode Resistance (ohms) 30Ω 5Ω Electrodes 1 by 1440mm 4 by 1440mm, a minimum of 1500mm apart Comments Refer to drawing STD_E0144 for installation details. Specific design required as per clause 7 of this standard. Specific design required as per clause 7 of this standard. Or Transmission, signals and no 1500V All locations 5Ω 4 by 1440mm, a minimum of 1500mm apart 10 Appendices NA PRINTOUT MAY NOT BE UP-TO-DATE; REFER TO METRO INTRANET FOR THE LATEST VERSION Page 7 of 7