The evaluation of overvoltage during short-time additional earthing of healthy phase for fault location in MV networks

The paper is focused on the operational experience with an automatic system for additional earthing of the faulty or healthy phase during an earth fault. The system is primarily used for limiting of a fault current in the point of the fault by earthing of the faulty phase during an earth fault. The equipment for additional earthing of faulty phase can also be used for short-time connection of healthy phase to earth fault location. There are fast circuit breakers for additional earthing in the substation and the cycle close-open is shorter then time for tripping of overcurrent protection in the outgoing feeder-bay (100 ms). This method of fault location in MV network could bring additional overvoltage which stresses the insulation of MV networks elements, similar as described in [7], [8] and [9]. This paper presents the simulation and experimental verification of this phenomenon and gives the recommendation for choosing the healthy phase for minimizing the negative influence of this location technique.