Investigating the Effects of Adding Distributed Generation Resources to the Distribution Networks on their Protection System Performance

The addition of distributed generation resources to the distribution networks leads to changes in the amplitude and direction of the short circuit current, which in turn causes malfunction of over current relays in these networks. Given that redesigning the protection system of these networks is economically costly and technically challenging, the present study proposes a method to prevent potential problems for the network’s protection system by limiting the capacity of installable DG on the network buses. In this regard and as the main feature of the proposed approach, first, this paper tries to fully describe all the problems arisen from integrating the distributed generation resources into the distribution network’s protection system. Based on this, these problems are categorized into five groups including, lack of back up relay operation, time coordination disruption between relays, unintentional creation of isolated areas and two kinds of unwanted operation of relays. Finally considering the worst-case scenario for each of these problems and in order to avoid them, the maximum potential capacity of the distributed generation resources which can be installed on each bus of a standard sample network has been determined.