Considerations and improvements of configuration and protection of a 72 kV mining resistance neutral grounded system

This paper provides a discussion on grounding of the neutral of a 72 kV mining system supply with high and low resistance grounding (HRG/LRG), and proposes improvements to the configuration and protection associated with neutral resistance grounded (NRG) systems. For safety reasons, the ground potential rise (GPR) of the switchyards in the mine is limited to 100 Volt. In addition to the reduction of the mine switchyardpsilas ground resistance, the line-to-ground-fault current is reduced by inserting NGR between the ground and the neural of the source transformer. The paper examines the technical viability of extending techniques used for systems of lower voltages such as those used on some generatorpsilas HRG, to a 72 kV mine system. With the advancement of numerical relays and the economical availability of such relays improved protection systems could be adapted for the subject installations.