Author(s):
Date presented: July 22nd, 2018
Andrew Blakeley-Smith
BSc (Hons) CNAA, CP Eng, MIEAust, MIRSE
Director, Andrew Blakeley-Smith & Associates
Jan Stelmach
MSc Electrical Eng, MIEAust CPEng NER APEC Eng.
Director, D’ACE Design and Consulting Engineers
SUMMARY25kV railway electrification implementation started in Europe, was implemented in the UK in the late 1950’s and wasmigrated to Australia in the mid 1970’s. Although some modification and additions were made to accommodate localconditions such as the use of the Multiple Earthed Neutral (MEN) in utility distribution systems, even at that timetechnology had advanced to the point where some specification requirements really needed reviewing but, lackingpractical experience, remained unchanged. This has become more pressing by the 21st century with the advent of, forexample, Optical Fibre technology, LED signals, axle counters and the demise of the Signal Post Telephone reducingS&C circuit lengths, questioning the requirement for Booster Transformers. Never the less, many specifications stillquote the standards of the 1950’s.Unquestioning compliance with requirements appropriate to these standards can have a significant cost, particularlywhere existing railways run parallel to, but have no running, over 25kV lines, new or to be electrified, or achievingseparation of earthing systems in existing complexes or new developments over or immediately adjacent to a 25kVrailway. The resulting design may be overly complex, time consuming, expensive or, in practice, realisticallyunachievable.Recent injection testing of nominally non-immune signalling equipment and short circuit and normal running EarthPotential Rise (EPR) testing on complex Central Business District (CBD) sites has shown that, when the going getstough, these issues must be looked at anew from first principles and old rules not followed blindly, if time and costblowouts are to be avoided. In some instances, by failing to recognise the nature of a problem, such as EPR arising fromlightning, outdated costly design requirements may not even be effective.
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