Impact of distributed generation on relay coordination

The reliability and stability of the power system decreases with abnormal operating condition of the protective system which may be caused due to overvoltage, under-frequency, overload etc. and leads to interruption of the supply, and may damage equipment's connected to the system. To maintain system stability and reliability it is necessary to have a protective system which operates as quickly as possible, isolates smallest part of the system under fault. For this purpose it is necessary to have coordination between the protective devices to assure safe operation. Over-current relays especially Inverse Definite Minimum Time (IDMT) relays are most commonly used protective device in the distribution system. It is vital that during abnormalities or faults, the IDMT relays must be capable to isolate only the faulty part of power system from the healthy system. A population based optimization algorithm called Teaching-learning based optimization algorithm is used in order to get optimum settings of TMS & PS. The CTI associated with primary and backup relay pairs is getting violated due to changes in fault current level. Thus coordination between primary and back up relays fails in the presence of distributed Generation. Hence interconnection of DG in the distribution system causes adverse impact on protection coordination.