Concept and practical testing of single pole operated earthing breakers in an urban MV cable network

The most important advantage of MV systems with isolated neutral or with Petersen coils is to allow uninterrupted power supply to the consumer in case of a single phase-to-ground fault even if it persists for a longer period. The shortcomings of those systems are: • possibly critical touch- and step voltages especially in larger systems with single phase-to-ground fault currents substantially higher than 100A • danger of double phase-to-ground faults caused by high transient voltages due to arc extinctions and restrikes at the fault location (intermittent faults) • possible destruction of the insulation of neighbouring cables by the fault current and transition to 2- and 3-phase faults.