Surveying the effect of distributed generation (DG) on over current protection in radial distribution systems

In the recent years, using distributed generation resources (DG), which are usually based on renewable energies, have noticeably developed on account of benefits for DGs such as reducing environmental pollutions and their interminable sources. Presence of DG influences the performance of distribution network that can be positive or negative. In this paper the effect of DG on the performance of an It-overcurrent (inverse time overcurrent) relay, used for current protection of the grid has been studied. The study has been performed from two points of views; it´s effect on relay operating time and relay reach (the certain distance that relay are set to protect). For studying DG´s effect on the performance of a Distribution system, the effect of a DG with different injection percent (to the max grid load), which is placed in different distances from the grid voltage source has been examined. The Simulations has been performed by using Matlab/Simulinki Simpower system software. The results show that the DGs injection percent and its distance from the It-over current relay significantly affect the It-over current relay protection performance.