9/9/2015 Frequently asked Electrical Engineering Interview Questions

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Why is star delta starter preferred with induction motor?Star delta starter is preferred with induction motor because it reduces the starting current about 3­4 times of the direct

current which causes the voltage to drop and hence it causes less damages and losses. Also, it increases the starting torque

and hence prevents from the damaging of the motor winding.

What are the differences between an alternator and a generator?Alternator and generator, both devices have the same basic functionality. They both convert mechanical energy into

electrical energy and they both have the same principal of electromagnetic induction. The main and only difference

between these two devices lies in the construction. Alternator has a stationary armature and a rotating magnetic field for

high voltages, while generator uses stationary magnetic field and rotating conductor which rolls on the armature with slip

rings.

Other than these two questions, three more important electrical engineering interview questions and answers are asfollows:

Why AC systems are more used or preferred over DC systems?The reasons why AC systems are more widely used and more preferable than DC systems are as follows:

1. It is comparably easy to maintain and modify the voltage of AC electricity for transmission and distribution than it is

for DC electricity.

2. The entire plant cost, ie, circuit breakers, isolators, transformers, etc is much lower in comparison to that of DC

transmission.

3. All the power stations produce AC electricity, and hence it is advantageous and also easy to use AC rather than

converting it and using DC.

4. AC is practically a sine wave current, and hence in case of a large fault in the network, the sine wave will naturally

tend to zero at some point and hence it is very easy to interrupt it in an AC system rather than in a DC system.

Why is negative feedback more preferable in control system?The role of feedback system in control system is to check deviation from the desired result, that is, it takes the sample

output back to the input and compares the output signal with the input signal for any kinds of error. Negative feedback

results in a better stability for the system. It rejects any kind of disturbance signal and is less sensitive to any kind of

parameter variations.

What is reverse power relay?

9/9/2015 Frequently asked Electrical Engineering Interview Questions

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Reverse power relay are used for the protection of the generating stations. The generating stations feed power to the grid

and in case when the generating stations are off, there is no generation in the plants and it pulls off power from the grid.

To stop this power flow from the grid to the generating stations, reverse power relays are used.