Transient Power Frequency Overvoltages Transferred to Low Voltage Networks from the EPR of HV and MV Transformer Stations

The transient power frequency overvoltages appearing in the low voltage (LV) supply networks are causing increasing number of damages both in electrical equipment (household, office etc.) containing electronic control parts and in telecommunications apparatus especially in their line cards. Accordingly to the practical experiences one significant source of these transient overvoltages is the transfer of the earth potential rise (EPR) caused by the earth faults occurring in the high voltage substations. The paper describes the ways of identification of the EPR caused by phase-to-earth fault in high voltage (HV) networks and double earth faults in medium voltage (MV) networks with not directly earthed neutral. The mechanism of the voltage transfer and the relative importance of the different parameters in the magnitude of the transferred voltages are also investigated.