Rahman Dashti

During a short circuit, regardless of the damage it causes to the short circuit point due to an electric arc, it also causes high dynamic and thermal stresses to the power system equipment such as overhead lines, cables, transformers and power switches. And the passage of this current requires equipment that can withstand this current, and to cut it, we need switches with high cut-off power, which imposes a heavy cost on the system. For this reason, it tries to limit the fault currents so as not to damage these equipments. Therefore, in order to protect the network equipments, it is necessary to quickly detect the fault point and cut it off at the right time. To do this, it is very important to relay. And power switches are used under the command of relays. In case of an error in a point of the network, the relays identify it and then separate the damaged part from other parts of the network by power switches, but this point It should be borne in mind that the network protection relays should be coordinated with each other, because if the relays are misdiagnosed, the desired relay will not separate the faulty part of the network, or if the network separates other non-defective parts from The network disconnects, so the best way to protect the power network by the relays is to coordinate between the relays. The purpose of coordinating the relays is to select the shortest fault path to disconnect the damaged network with the highest operating speed.