Practical Substation Earthing Design for Mine Site

Abstract

During an earth fault a phase conductor is connected to earth and fault current starts to flow between the phase and earth. Part of this earth fault current is injected into the ground to return back to the source and part of it flows via an earth return conductor. The current injected to the earth mass creates an earth potential rise in the vicinity of where it is injected. This earth potential rise creates touch potential, step potential and transfer potential. A mine site, especially a coal mine, requires lower touch potential and the earth fault current is limited to a lower value using neutral earthing resistor (NER). When the earth fault current on the secondary side of a delta-star transformer is limited using the NER the earth potential rise is also limited to a lower value which makes it easier to comply with the standards. This presentation will deal with the problems encountered in designing earthing system for a mine site complying with AS 2067-2008 and other relevant Australian Standards. It will discuss practical solutions and will cover the determination of allowable touch and step potentials, transfer potential as well as separation of high voltage and low voltage earthing systems.