Overvoltages on distribution systems

In the framework of live working in a MV network, a cable-transformer system can be switched-off or switched-on. The ferroresonance phenomenon can occur during this procedure with very dangerous overvoltages. The metal oxide varistor (MOV) can fail during this phenomenon. The paper investigates the determination of the critical feeder length of cable, which will damage MOVs. A transformer model taking into account both the saturation and the hysteresis is proposed. The digital simulation concerning de-energization of the real configuration of the cable-transformer system is studied and the results obtained are verified by field tests.