Operational Experience in Determining the Earth Fault on Resonant Grounded Networks

Resonant grounding of the medium voltage (MV) network’s neutral point improves the power quality and creates conditions for development of more reliable network. By changing the way of the MV network grounding, conditions for relay protection of single phase fault (earth fault) are changed due to reduced value of zero sequence current during earth fault and demands on the relay protection are increased. Protection system is not able to selectively detect earth fault with high transient resistance and repetitive current earth faults in cable network, so it requires more sensible approach. In case of fault detection, technically more demanding fault indicators must be used. This article will show experiences in detecting earth faults in resonant grounded MV network of Elektra Zagreb.