DESIGN AND ANALYSIS OF PROTECTIVE RELAYS FOR PROTECTION OF THREE PHASE INDUCTION MOTOR

Abstract

Every electrical equipment has to be monitored to protect it and provide human safety under abnormal operating conditions. Electric motors play a vital role in everyday life from electricity generation plants, industries and domestic uses. Majority of the industrial loads are induction motors and electric motors are used in electrically powered rail vehicles such as electric multiple units and long distance trains. It shows how much important it is to protect induction motor from various abnormal conditions. Simulation software are very useful for educational and industrial purpose where you can simulate a system and check its performance under various condition before creating the actual system. Here various protective relays are simulated in MATLAB and Proteus professional software and various results were obtained. In this dissertation, overcurrent relay, undervoltage relay, thermal relay and digital negative sequence relay are simulated and under various operating conditions the operation of relay is studied. Microcontroller based relay is used to protect the motor from over temperature. A motor can be slightly overloaded only if the temperature of the motor is not high and if the temperature of the induction motor is high it should not be overloaded as it will further increase the temperature of the motor and it will reduce the lifetime of the motor. Overcurrent relay will operate if the current in any phase of the motor will increase and it will protect the motor against various faults. Further, digital negative sequence relay is simulated and its operation is studied under line to ground fault and it is successfully operated under the fault condition. Now a days a major research is going in the field of digital relays. These relays are more capable in detecting faults and they have fast operation.