Determination of the Earth Fault Factor in Power Systems for Different Earthed Neutrals

This paper proposes an analytical method to calculate the earth fault factor (EFF) in power systems, under different neutral earthed possibilities. The magnitude of the EFF depends on the way the neutrals of a system are earthed and influences some important aspects in power systems as the sensitivity and selectivity of relays, the value of short-circuit currents, the overvoltage between lines and earth, the determination of arrester rating and the system insulation level. The obtained results are compared with the values of EFF referred in International Standards.