Case study for assessment of high risk earthing on distribution assets

Electrical power utilities typically base distribution earthing design on a standard design philosophy. Utilities will apply either common or separately earthed standard designs to suit a set of criteria that is aimed at achieving the safest and most manageable earthing configuration for the distribution network. Unfortunately the method of implementation of these standard designs has resulted in common earthed substations which generate significant earthing risk throughout distribution networks, higher than most Australian Standards would recommend. This paper identifies the recommended assessment techniques and correct testing methods that have been proven in analysing a high risk distribution network in a Tasmanian township. The case demonstrates the required mitigation strategies and future design considerations for the area to control risk to as low as reasonably practicable, and also highlights the need for power utilities to consider nonstandard designs in order to responsibly manage the changing distribution network.