History of earthing and the impact on coal mining

The use of earthing in electrical power reticulation has an interesting history. Initial power distribution systems did not deliberately reference the phase conductors to earth. Later, depending on the application, there was a bifurcation of earthing practices, with some systems solidly earthed through low impedance resistors and some loosely earthed through high impedance resistors. The coal mining industry in Australia has converged to high resistance earthing. The supply is removed on the first earth fault to ensure that the fault is not escalated on the occurrence of a second earth fault. While this has safety benefits, there are challenges for the design of sensitive earth leakage protection. This is further complicated with the introduction of Variable Speed Drives (VSDs). This paper charts the history of earthing and how it has influenced the way that earth fault protection is implemented in coal mines, both in Australia and overseas.