Enhancement of overcurrent protection in active medium voltage distribution networks

Using renewable sources to meet the load demand in the distribution level has become more economical and prevalent. The integration of these sources has impact on the load flow direction and magnitude. These changes can affect the operation of overcurrent (OC) relays as the main protective device in medium voltage (MV) distribution networks. In other words, the changes in the current magnitude and direction will result in misoperation of the OC relays during normal conditions of the network. In addition, the variation of the output generation of renewable sources due to weather condition changes, makes it difficult to define appropriate settings for OC relays. In this paper, a novel idea for improvement of OC relay operation in MV distribution networks in the presence of photovoltaic (PV) sources is presented. The proposed protection system is based on the augmentation of current and the reduction in voltage during the fault. Therefore, a combination of directional OC and under-voltage (UV) protection can distinguish between faulty and normal conditions. The proposed method is simulated using EMTDC/PSCAD software. The results show that the proposed method can effectively protect the MV distribution network containing PV sources.