New adaptive algorithm for detecting low- and high ohmic faults in meshed networks

Statistics show that the major portion of grid faults are earth faults. Conventional relays are designed only for low ohmic earth faults under stationary conditions and for non meshed systems. They can handle neither high ohmic earth faults, which occur especially in rural networks with overhead lines, nor intermittent earth faults in compensated cable networks. Additionally all algorithms are very sensitive to real and virtual crosstalks from the load current to the zero-sequence-system, which occur in every meshed system. As a consequence, very often the earth fault is not recognized or the wrong feeder is selected to be healthy. In the paper the reasons for the crosstalk from the load current to the zero-sequence-system, the influence even to transient relays and the benefits of the new adaptive algorithm are explained in detail. The theoretical explanation is completed with the presentation of real field results from a very large meshed distribution network.