Performance analysis of a transient-based earth fault protection system for unearthed and compensated radial distribution networks

This paper deals with the protection against earth faults in distribution networks with unearthed or compensated neutral. A transient-based protection system is proposed and assessed through electromagnetic transient program (EMTP) simulations. The fault detection algorithm is based on the estimation of the angle between the zero-sequence voltage and current phasors. The estimation is carried out at the dominant transient frequency of the network response within the first milliseconds after the fault. The implementation of an improved filter and a zero-padding process allows for the identification of high resistance faults with a relatively low sampling frequency. An operation zone is proposed and assessed, also for unbalanced or mixed bare and cable line networks. The performances of the protection system are evaluated for a distribution network in both the cases of unearthed and compensated neutral through a Monte Carlo method that considers the fault resistance, incidence angle and fault location variations as random variables in the EMTP simulations.