Relay coordination and harmonic analysis in a distribution network with over 20% renewable sources

Distributed generation changes the radial nature of distribution systems and affects the performance of the protection system. Power quality and system protection are interwoven and cannot be separated. Protection engineers need to be aware of the effects that power quality (PQ) has on the distribution system and the power quality engineer must understand the effects the protective relays have on the distribution system. The ever increasing addition of distributed generation (DG) in the distribution system has complicated the issue of the relay coordination and protection in general. The addition of DG resources impacts on the distribution relay protection of the system. This paper focuses on the impact of the addition of renewable energy sources (RES) into the distribution system. One network is proposed to have less than 20% of the circuit loading added to it by RES, while the second network has multi renewable sources (>20%) added. Harmonic analyses of the two networks were carried out, supported by ETAP analysis software. First, it was shown that there were no appreciable changes in the protection systems when the addition of the DG was less than 20%. With Huge penetration of DG, there is need to determine new protection device locations for relay coordination and measure the different harmonic contents.