A New Transient-Based Earth Fault Protection System for Unearthed Meshed Distribution Networks

This paper deals with the protection against earth faults in medium voltage meshed networks with unearthed neutral. A communication-supported protection system is proposed and assessed through numerical simulations. The protection system is based on the use of directional relays installed at both ends of each line of the network. Each relay communicates by sending permissive signals following the so-called directional comparison overreaching transfer trip scheme. Each directional relay implements a new transient fault detection algorithm based on the angle between the zero-sequence voltage and current phasors. The phasors are estimated at the dominant frequency of the network transient-response within the first milliseconds after the fault, which range can be evaluated by means of a simplified circuit equivalent representation. The performances of the protection system and the detection algorithm are evaluated for different network configurations. By using a specifically developed co-simulation tool that interfaces EMTP-RV with Matlab, the influence of the communication latency is also analyzed. A Monte Carlo method is applied to analyze the effects of fault resistance, incidence angle and fault location variations. Results of a real-time simulation obtained in the Opal-RT environment further support the applicability of the algorithm.