# Electrical Interview Questions – Part 1

## 1. What is “pu” in electrical engineering?

Pu means per unit and this will be used in the diagram of a single line of the energy system, it is like a large electric circuit without components (generators, transformers, loads) with different classifications (in MVA and KV).

In general, the largest MVA and KV classifications of the component are considered base values, then all other classifications of components will return to this base. These values are called pu values. (p.u = actual value / base value)

## 2. Why link is provided in neutral of an ac circuit and fuse in phase of ac circuit?

The link is provided at a neutral common point in the circuit from which several connections are made for the individual control circuit and, therefore, is provided in the form of a link to withstand high amperes. But in the case of a fuse in the phase of the AC circuit, it is designed in such a way that the rating of the fuse is calculated only for the particular circuit (that is, the load). Therefore, if a fault occurs, the fuse connected to the particular control circuit will only turn off

## 3. What is a tapโchanging transformer?

It is a transformer that has one or more output cables, so the switch can be used to change the output voltage of a reference cable.

## 4. What is VCB?ย

Vaccum Circuit Breaker (VCB) is normally used to break circuitย  to prevent excess current during a short circuit.ย A vacuum circuit breaker is a type of circuit breaker in which the cooling of the arc takes place in a vacuum. This technology is suitable for medium voltage application. VCB can used upto 11kV.

## 5. 1 Ton is equal to howย  many killoWatt?

1 ton = 12000 BTU/hr Convert BTU/hr into Horse power
12000* 0.0003929= 4.715hp
1 ton = 4.715* 0.746 = 3.5 KW

## 6. Why use VCB at High transmission system? Why can’t use ACB?

Actually the thing is vaccum has high arc queching property compare to air because in VCB, the die electric strength equals to 8 times of air. They y alway vaccum used as inHT breaker and air used as in LT.ย

## 7.ย what is the diff. btwn. electronic regulator and ordinary rheostat regulator for fans?

The difference between the electronic regulator and the ordinary one is that in the electronic register. The power losses are smaller because as we slow down the electronic record. provide the necessary power for that particular speed, but in the case of an ordinary rheostat type register. the waste of energy is the same for each speed and energy is not saved. In the electronic regulator, the triac is used to control the speed. By varying the firing angle, the speed is controlled, but in the dynamic control the resistance is reduced in steps to achieve the control of the speed.

## 8. Whats is MARX CIRCUIT?

It is used with generators to charge a number of capacitor in parallel and download them in series. It is used when the voltage required for the test is greater than that available.

## 9.ย What is resonant peak?

Resonant peak is defined as the maximum value of the closed loop transfer function. A large resonant peak corresponds to large overshoot in the transient response

## 10.ย What is Resonant Frequency?

The frequency at which the resonance peak occurs is called the resonance frequency. The resonance frequency explains the speed of the transient response

## 11. What is Gain Margin?

The gain margin is defined as the reciprocal of the magnitude of the open loop transfer function at the phase crossing frequency. The profit margin indicates the amount by which the gain of the system can be increased without affecting the stability of the system.

## 12.ย  What isย Phase Margin?

The phase margin is the amount of additional phase shift in the gain crossing frequency required to bring the system to the edge of instability.

## 13.ย Difference between megger test equipment and contact resistance meter test instruments?

The Megger test equipment is used to measure the electrical resistance of the cable, the continuity of the conductor, the phase identification, while the test instruments of the contact resistance meter are used to measure the low resistance as relays, contactors

## 14.ย Which motor has high Starting Torque and Staring current DC motor, Induction motor or Synchronous motor?

The motor of the DC series has a high starting torque. We can not start the induction motor and the synchronous motors under load, but we can not start the DC series motor without load.

## 15.ย what is ACSR cable and where we use it?

ACSR means aluminum conductor reinforced with steel, this conductor is used in transmission and distribution.

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