Andrew Blakeley-Smith, BSc(Hons), MIEAust, MIRSE
Director Andrew Blakeley-Smith & Associates
Allan Neilson, BE(Elect), MIPENZ, FIRSE
Manager Traction & Electrical Engineering, ONTRACK – (New Zealand Railways Corporation)
Earthing & Bonding is an essential element in an a.c. electrification environment to ensure personnel and property safety. It is a highly interdisciplinary and iterative activity in the design process of a new 25kV a.c. railway system and many of the fundamentals are not widely understood - yet the underlying principles do not require much more than a basic appreciation of Ohms Law. Personnel hazards resulting from induction and earth potential rise (EPR) are, in practice, very rare events however care must be taken when focussing on the strict numeric requirements of standards that we do not lose sight of the big picture, both in terms of immediate and consequential hazards. These can only be avoided by a top down approach to earthing and bonding, and therefore compromises in design are inevitable.
The design of earthing and bonding systems is well documented by various railway administrations but frequently applied inappropriately as the origin of some of the practices and criteria often seems to have been forgotten. Solutions are frequently subject to subjective philosophical decisions and much faith is often placed in highly accurate modelling derived from input data and assumptions of dubious accuracy. The international signalling fraternity has made great strides in recent times in a top down approach to their contribution to overall rail safety with a consequent harmonizing of standards which the authors would like to see extended to earthing and bonding practice.
This paper aims to ensure that all key aspects of this cross-disciplinary subject are understood, reviewing some past historical practices adopted by different rail authorities and sets out parameters for good design and installation practices applicable to both Australia and New Zealand in alignment with contemporary international practice. This paper builds on the paper presented by the authors at the CORE 2008 conference in Perth.
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