ELECTRICAL QUESTIONS AND ANSWERS|Online electrical engineering & Electrical Interview Questions

Wednesday, November 17, 2010


Hey Amit first of all thanks for asking your doubts.Let me apologize for not posting the answer for your questions for a long time.I couldn't post because of internet problems and other work issues.

1.When there is a sudden loss in the demand what happens to the transformer and generation? 
Consider a train running at 50 km/hr with 20 coaches.Assume that 5 coaches detaches when the train is running.What happens at this time is train will be experiencing an increase in speed and the engine driver has to reduce the speed to bring the train speed to 50 km/hr.

Similarly in a Power System,when there is a sudden loss in load or demand the speed of turbine(steam turbine, hydraulic turbine..etc)  driving the generator increases.So a SPEED GOVERNOR is employed to reduce the speed of the turbine by limiting the input to the turbine.

Consumers need a constant voltage profile for proper functioning of the electrical equipments.But when there is a sudden loss in load, generator terminal voltage is increased.We know that field coils are used instead of permanent magnets in generator.The field coils are excited using a exciter.If we adjust the input to the exciter, the magnetic field changes thereby changing the generator's terminal voltage.this is done by using AUTOMATIC VOLTAGE REGULATOR(AVR).

Speed Governor controls Real Power generation and the frequency of supply.
AVR controls Reactive Power generation and the voltage.

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