Date:MAR 94 25kV A.C. Electrified Lines - Traction
Page 1 of 6 Part A Synopsis This is issued by the to define the Boards requirements for continuity bonding on railway systems. This will ensure a continuous return circuit and that currents in the return circuit do not interfere with the operation of signalling circuits or equipment. It will also allow paralleling of return circuits to reduce overall return resistance. Approval and authorisation Submitted by:.............................. 25kV A.C. Electrified Lines - Traction Nominated responsible manager Approved by :.............................. Chairman, Electrification & Plant Subject Committee Authorised by :............................. Board Member, Engineering This document is the property of the, it shall not be reproduced in whole or in part, nor disclosed to a third party, without the written permission of the Director, Engineering Standards. Copyright 1994 Published By s Railway Technical Centre Derby
Issue / Revision record This standard will be updated when necessary by distribution of a complete replacement. Amended or additional parts of revised pages will be marked by a vertical black line in an adjacent margin. Issue Rev Date Comments 1 A Mar. 94 Original Document Responsibilities and distribution Controlled copies of this standard shall be worked to by all staff responsible for the specifying, designing, and installing continuity bonding on electrified railway systems. This standard shall be distributed to all relevant T & RS Engineers, Electrification Engineers, S & T Engineers and Civil Engineers within each business. Withdrawn Document Contents Page 2 of 6 Section Description Page No. Part A Synopsis 1 Approval & authorisation 1 Issue/Revision record 2 Responsibilities and distribution 2 Implementation 2 Supply 2 Contents 2 Part B Implementation The provisions of this standard are mandatory and apply from the date of receipt. Supply Controlled copies of this standard must be obtained from the TDCC Manager, Document Services, Dovedale House, RTC, London Road, Derby, DE24 8UP. 1 Purpose 3 2 Scope 3 3 Definitions 3 4 Continuity bond requirements 4 Appendices A References 6 Uncontrolled copies are also available from the same source of supply
Part B Withdrawn Document Page 3 of 6 1 Purpose 1.1 To define the mandatory requirements for traction bonding on the return current circuits of an alternating current (A.C.) electrified railway. 2 Scope 2.1 For new electrification schemes the requirements of this document shall be implemented prior to the energisation of the electric traction equipment concerned. 2.2 For existing electrification schemes, where the requirements of this document differ from those previously implemented, change to the existing installation shall be implemented where reasonably practicable to do so. 3 Definitions 3.1 Continuity bonding Continuity bonding is the generalised term governing all electrical connections made to the return rails to provide a continuous circuit back to the electricity supply distributing source. The term also covers electrical connections made to the return rails or midpoint connections of impedance or resonating bonds in order to provide a direct path, or increase the number of paths, for the current to return to the distributing source. For the purposes of this standard any other equipment carrying return traction current such as impedance or resonating bonds shall also be considered as continuity bonds. 3.2 Step Potential When an earth electrode is subject to a potential rise, the surrounding area is subjected to a potential gradient which is greatest at the earth electrode. The actual potential reduces to true earth potential or zero at some distance from the electrode. "Step Potential" is the potential difference between the persons' feet caused by the potential gradient.
Page 4 of 6 Definitions (continued) 3.3 Touch Potential This is the potential difference between a persons' hand which is touching an exposed conductive part and any other part of the body which is touching an exposed conductive part at a different potential. 4 Continuity bonding requirements 4.1 The traction return system shall be connected so as to ensure its continuity. 4.2 Any exposed conductive path that may be subject to 25kV due to flashover or by inadvertent contact with live conductors shall be connected to the traction return system so as to ensure rapid disconnection of supply under such fault conditions. 4.3 The traction return system shall be installed so as to ensure its connection to the general mass of earth via the foundations of the overhead line structures or other means which may be considered necessary if overhead structure foundations are not available. 4.4 The traction return rails and the exposed conductive paths connected thereto shall not rise in potential above 50V rms A.C. under normal load and 430V rms A.C. under fault conditions with respect to the mass of earth. (Note: A European Standard "Safety, grounding and protection - fixed equipment" is in draft form.) 4.5 The traction return system shall be arranged so that no step or touch potentials arise greater than the values given in 4.4 above. 4.6 Electrical conductors connected to the traction return system shall be rated to carry the traction return current. 4.7 Arrangements shall be made to ensure that surface or buried metal pipes, earth electrodes and other metallic objects do not develop hazardous potentials through induction from the traction current or voltage, and are not damaged by any traction return current which flows in them.
Page 5 of 6 Continuity bonding requirements (continued) 4.8 Where non-metallic or reinforced concrete structures are so close to live equipment that they are at risk from flashover, arrangements shall be made to ensure that such flashovers are discharged to the traction return current path to give rapid disconnection from the supply and to avoid damage to the structure and to the overhead lines. 4.9 The normal method for ensuring that hazardous step and touch potentials do not arise is by equipotential bonding. 4.9.1 In cases where equipotential bonding, for the purpose of providing a path for the fault current or for avoiding hazardous step and touch potentials, would result in electrical interference or damage to other electrical systems, or damage to structures, pipes, etc., there is a conflict of requirements. In such cases, the design shall be arranged to ensure that such interference and damage are contained within acceptable limits while satisfying the requirements of clause 4.4. The preferred method for resolving such conflicting requirements is physical separation, in order to remove the requirement for equipotential bonding. 4.9.2 Where physical separation is not possible, insulated barriers or other means shall be employed to prevent a person from being simultaneously in contact with exposed metalwork which is bonded to the traction return path and exposed metal which is not bonded, unless it is shown that no hazard arises from permitting such contact. 4.10 The detailed bonding arrangements shall be subject to scrutiny and acceptance by the Signalling function, as detailed in the appropriate, to ensure that the functioning of track circuits is not jeopardised. 4.11 Where applicable the installation of the traction return system shall result in acceptable telecommunications interference levels as defined in 4.2.12 of GM/TT0094.
Appendix A References Withdrawn Document Page 6 of 6 Reference Location. A.1 GM/TT0126 Prod & mods of bonding plans and installation Part B 4.10 of bonding etc. (not NSE) A.2 GM/TT0129 Production of drgs and installation of negative Part B 4.10 bonding on NSE. A.3 GM/TT0094 Electromagnetic compatibility between railways Part B 4.11 and their neighbourhood