Evaluating the impact of distributed generation on protection system coordination using protection miscoordination index

Distributed generation (DG) has been considerably increased for several years. However, it may provide negative impacts to the connected distribution system. One important problem is the protection system miscoordination which decreases system reliability. This paper proposes a method to quantify the impact of a DG on protection coordination by using Protection Miscoordination Index (PMI), the value of which shows the probability that the protection miscoordination will occur in the system. The constraints used to indicate the coordination problems are presented and tested. The obtained PMI results from various cases are analyzed. In addition, the maximum allowable capacity of a DG that can be installed to maintain the protection coordination is obtained using PMI.