The "Short-term Isolated Star Point Grounding" to Detect Earth Faults in Compensated Networks – The Concept

Many medium-voltage power supply grids, especially in Europe, are built as a compensated design. The earth fault compensation coil (arc surpression coil, ACS) connected to the grid feeder compensates the capacitive grid currents in case of an earth fault, which ensures low residual currents at the fault location. However, this makes earth fault detection, especially the directional detection of single-pole faults, much more difficult. In this paper an innovative algorithm for directional earth fault detection, e.g. with an overhead line indicator, in compensated networks is presented. This algorithm is based on altering the star point grounding of the network. To determine the location of an earth fault, the network earthing is changed from compensated to isolated temporarily by deactivating the compensation unit. During this period, the direction of the fault location can be reliably detected at various positions in the network. First, the physical background of this method is explained. Then the proposed algorithm is validated by network simulations, with different scenarios being investigated. The results of the simulations are discussed, and a practical recommendation is given.