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Underground Mine Earthing Study

AEE recommended an earth grid design for this remote mine’s Power Station that satisfied step and touch potential limits at the power station and at the adjacent fuel storage tank area. The design was developed using GroundMat software (© SKM Incorporated) and  based on a measured soil resistivity of 66 Ohm-m.

Six off 6.0 metre earth rods around the earth grid periphery were recommended to augment the six off 2.4 metre earth rods already installed inside the earth grid area.

With a calculated earth resistance of 1.51 Ohm, the grid was suitable for either TN or IT operation of the mine 11 kV supply where:

  • the TN option was with a solidly earthed neutral, &
  • the IT option was with a high resistance neutral earthing resistor where the power station earth grid served as both the power station earth and underground plant earth.

An earth fault return current split of 50% via the 11 kV cable screens and 50% via the body of the earth was assumed for the earth potential rise study in the TN system.