The "Short-term Compensation Change" to Detect Earth Faults in Compensated Networks

Abstract

Many power grids, especially medium-voltage level supply grids, are operated in compensated mode. The earth fault compensation coil (arc suppression coil, ASC) connected to the main power feeder compensates the capacitive network currents in case of an earth fault. Consequently, the fault current at the fault location is drastically reduced. Due to the low touch voltage, the network does not have to be necessarily switched off during a fault occurence. Therefore, supply reliability is increased. This, however, makes earth fault detection, in particular detecting the direction of single-pole faults, considerably more difficult. In this publication an innovative method for directional earth fault detection, e.g. using overhead line indicators, in compensated networks is presented. This algorithm is based on altering the amount of fault current compensation by the compensation coil. In order to determine the location of an earth fault, the network is temporarily operated in the under-compensated mode instead of slightly over-compensated mode. Therefore, zero-sequence currents of faulty feeders shift to more capacitive values. By evaluating this shift of the zero-sequence current, the direction of the fault location can reliably be detected at different positions in the network. First, the physical background of this method is explained. The algorithm is validated by network simulations, where different scenarios are examined. The results of the simulations and advantages and disadvantages are discussed and the method is compared to established methods.