Mitigating the risk of an equipotential rise voltage arising on the HV side of an 11kV:415V or 22kV:415V distribution transformer being transferred to the LV network is traditionally by either ensuring that the resistance to earth of a combined HV and LV earth is very low often by using a number of parallel earths, or by using two separated earths. .
These face challenges of cost and feasibility. Recommended guidelines are described on the options including resistance to earth, separation distance, protective devices, increased insulation, arresters, resistive earthing; and addressing induced voltages in earthing leads.
Examples are presented