Detection of broken conductor with ground contact faults in medium voltage power networks

A major problem concerning the operation of medium voltage power networks refers to the neutral-point grounding system. Several technical solutions are in use, none of them being completely satisfactory. One criterion to appreciate the efficiency of a grounding system is the ability of the network’s protective system to accurately detect various types of faults such as broken conductor with ground contact faults. This type of fault make a relatively important figure (3 to 10 %) in the total faults statistics for a medium voltage network. In order to detect such faults, the sensed variables are the zero-sequence voltage and the neutral-grounding current. In this paper an analytical and computational analysis is performed to see how various fault and network parameters affect these variables, assuming different grounding systems. Measurements made in two real medium voltage networks show good agreement with the theoretical results.