Impact of PV Sources on the Overcurrent Relays in Medium Voltage Distribution Networks

Integration of renewable sources to the power grids has become more economical and prevalent. These sources cause the load flow to change in the network which can affect the overcurrent (OC) relays as the main protective device in medium voltage (MV) distribution networks. In other words, increasing the current flowing through the lines will result in operating OC relays during normal conditions of the network. In addition, the generation of renewables varies due to change in the weather conditions, which can make it difficult to determine appropriate OC relay settings. In this paper the impact of Photovoltaic (PV) sources on the operation of the OC relays will be examined. It will be shown that the integration of PV sources bring about the operation of OC relays inadvertently due to changes in magnitude and/or direction of flowing current through the relays. To address this problem, recalculation of OC relay settings will be studied. EMTDC/PSCAD software is used in this paper to simulate the impact of PV source on the OC relays in the MV distribution network.