Motor is a device which converts electrical energy into mechanical energy. Motor protection is also essential. To protect the motor we are using the microprocessor based motor protection relay against various faults. Induction motors are widely used in industry because of their rigidity and speed-control flexibility. Therefore, the problem of induction motor protection attracted many researchers. The digital protection techniques that are used in digital relays provide better performance and higher accuracy than the conventional electromagnetic and solid-state relays.
The purpose of all protective relay designs is to protect the system or certain components against a variety of hazards and abnormal operating conditions and to limit the financial and operational liabilities incase of motor or system failure. Electromechanical or electronic elements ,this depends largely on the quality and reliability of the digital components utilized in the relay circuits. It is well recognized that the quality and reliability of these components are far superior to other comparative system components such as mechanical devices. Another very important consideration is the economics of the digital relay compared to the other types .Digital relays cost less then or at least equal to the cost of their electromechanical or electronic counter parts. Taking into consideration that the costs of electromechanical and electronics relays have been increasing, while at the same time and the cost of digital devices have been rapidly decreasing in the last decade. In the case of a large induction motor digital protection is far superior compared to other electromagnetic or electronic systems currently used. Since the digital relay is much more flexible than the other types the only limitation being the availability of the hardware and software specifically designed for this applications, expandable to take advantage of any future developments in the system integration and speed. The protection of motor(5HP) under all operating conditions that the conventional relay can protect it from. The relay will use the same input signals used to drive an electromechanical or electronic relay. The algorithm will calculate the operating conditions of the motor and will trip it only if it detects an abnormally that could cause damage to the motor or its drive.
Microprocessor-based digital protection relay for induction motor protection represents a major improvement over conventional electromechanical and electronic schemes. However, at the present time, it can be justified only for large motors ( > 1500 HP ) and for motors in critical installations.
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