Considering DGs Voltage Protection in Optimal Coordination of Directional Overcurrent Relays to Minimize the Energy Not Supplied

So far, the overall operation time of relays has been used as the objective function in all directional overcurrent relays (DOCRs) optimal coordination problems. However, it cannot guarantee that in an optimal coordination of DOCRs at presence of distributed generations (DGs), the reliability indices will reach the minimum value. The reason is the existence of DGs voltage protection at their connection point to the network. This protection plays a key role in determining participation of DGs in improving network reliability during fault conditions. However, in the previous studies in which the overall operation time of relays is considered as the objective function, the voltage protection of DGs is not taken into account. In this article, coordination between DOCRs and their interactions with the DGs voltage protection is considered in calculation of the energy not supplied (ENS). Also, instead of the overall operation time of the DOCRs, the ENS value is considered as the optimization objective function. A probabilistic hourly seasonal model has been used to model the renewable DGs and the network loads. Various scenarios have been simulated to demonstrate the efficiency of the proposed method over a standard 33-bus radial distribution network.