Exam Question
(a) What is the purpose of reverse power relay? (6)
(b) Explain with the aid of a simple sketch the working of a reverse power relay. (10)
Class 4 (4th Engineer)
MET
📅 Jan 2023
Reference Answer
### (a) Purpose of a Reverse Power Relay (6 Marks)
A reverse power relay is a directional protective device crucial for the safe operation of electrical power plants, particularly in marine applications where generators frequently operate in parallel.
Its primary purposes are:
1. **Prevention of Motoring**: The fundamental purpose is to prevent a generator from 'motoring'. This occurs when the generator's prime mover (e.g., a diesel engine or steam turbine) fails or is unable to provide the necessary torque to generate power. In this state, the alternator, still connected to the live busbar, ceases to be a generator and starts acting as a synchronous motor, drawing power from the other parallel-running generators or the shore supply. This reverse flow of power drives the failed prime mover.
A reverse power relay is a directional protective device crucial for the safe operation of electrical power plants, particularly in marine applications where generators frequently operate in parallel.
Its primary purposes are:
1. **Prevention of Motoring**: The fundamental purpose is to prevent a generator from 'motoring'. This occurs when the generator's prime mover (e.g., a diesel engine or steam turbine) fails or is unable to provide the necessary torque to generate power. In this state, the alternator, still connected to the live busbar, ceases to be a generator and starts acting as a synchronous motor, drawing power from the other parallel-running generators or the shore supply. This reverse flow of power drives the failed prime mover.
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