Performance of directional relays without voltage sensors: impact of distributed generation technologies

Abstract

Radial distribution networks are mainly protected w ith overcurrent relays, which are used for both earth a fault protection. Nevertheless, higher capacitive c urrent of underground cables can cause false tripping problem for overcurrent relay of a feeder during a line-to-grou nd fault on the adjacent feeder. The contribution of distrib uted generation (DG) to the fault current during a line- to-line fault also leads to a similar situation. To solve t his problem, a novel algorithm of directional relay has been pro posed in a previous work [1]. Based on the symmetrical compo nents method, the algorithm only uses current measurement s to determine fault direction and thereby suppresses th e cost of voltage sensors. This paper presents effect of distributed generator s on the directional algorithm by comparing the cases of Inv erterinterfaced Distributed Generators (IIDGs) in PV sys tems and of synchronous generators (SGs) in CHP plants. Results show good performances in both cases during earth faults. However, during line-to-line faults, this algorithm gives better results in case of IIDGs.