Improving the Differential Protection of Power Transformers Based on Fuzzy Systems

One of the causes of unwanted interruption in power transformers is its magnetizing inrush current. Due toits current conditions, this current causes the differential relay to misdiagnosis the internal fault of the transformer and leads to an incorrect cut-off command. In this paper, fuzzy systems are using to improve the differential protection of the transformer and to stabilize it against magnetizing inrush current. The basis of the proposed algorithm is that if the cut-off command is sending by the differential relay, by applying Clarke transform to the differential current and using fuzzy logic, the decision to send the cut-off command to the protection relays is made. The proposed algorithm is applying to a sample of the substation transformers model in Iran. The network is simulating in PSCAD/EMTDC software and the output of the simulation is transferring to MATLAB software to apply the proposed algorithm. The simulation results show the efficiency of the proposed algorithm in improving the differential relay.