Reverse Power Protection of An Alternator

Today’s complex power scenario consumer wants continuous power supply. Therefore now generator has become the ultimate power source and generator’s function is the heart of power system. Hence we should protect the generator from the occurring problems. Based on the form of input energy we can run the generator as a motor or generator. The generator used here is a synchronous machine and it is synchronized with the grid i.e. the bus bar.

The faults which can make major damage to both the generator and the economical situation are described below. We need to develop the generator which is fault tolerant and work very efficiently in abnormal condition also.

Condition for Reverse Power

Following are the possible circumstances in which reverse power condition may arise.

i) When number of units is working in parallel and failure of one unit may result in feeding the power from healthy units to the suffered unit.

(up to here)

ii) If one unit in all connected parallel units is overloaded and then its consequence would reduce the speed. Frequency decreases due to the decrease of speed and also generated EMF will get reduced. Finally at the critical stage, the machine will runs as a motor.

iii) The terminal voltage of the bus-bar is increased when load is suddenly thrown off. Alternator will run as the asynchronous motor if the above condition is not detected properly.

When the input to the turbine is stopped, the generator takes power from the bus-bar and it will rotate like the synchronous motor.  Transmission of electrical energy from the bus-bars to the machine in opposite direction during the motoring action of the generator is called as the Reverse power.

Effects of Reverse Power

The turbine will run as a load and the alternator will work as the synchronous motor during the reverse power condition. The Motoring protection is very useful for the prime mover and load coming on the generator bus-bar. The power flow from bus-bars to the generator is measured by the reverse power protection. Normally, in most cases the power taken is low such as 2% to 10%.  The electricity and power factor is dependent on the excitation level.

The direction of power flow in any one direction can be sensed by the single element directional power rely. The setting is based on the type of prime mover.