Electrical Engineering Interview Questions & Answers

Q. 1 Why star delta starter is preferred with induction motor?

Ans. There are three main reasons of using star delta starter-

1 Starting current is reduced three-four times then the direct current received from the source. This help in reducing the losses.

2 Because of this the starting torque is increased which reduce the damage the of motor winding.

3 Star delta circuit comes in contact with circuit during the starting of motor, which reduce the voltage three times and indirectly current is also reduced and starting become safe.

Q.2 State the application of storage batteries.

Ans. -Batteries are used for emergency lighting at hospitals, house holds, banks and rural areas.

-As a supply power source at telephone exchange and other boarding stations.

- For lighting diesel trains.

Q. 3 What is slip in an induction motor?

Ans Slip is the difference between the speed of rotor and flux speed. It is represented by the symbol 'S'.

Q. 4 What are the different methods of starting a synchronous motor?

Ans. By auxiliary motor. In this method the rotor of the synchronous motor is rotated by the auxiliary motor , due to which poles of the motor are exited and rotor field is locked.

By providing the damper winding:

Bar conductors are embedded in the outer periphery of the rotor poles and are short-circuited with the short-circuiting rings at both sides. The machine is started as a squirrel.

Q.1 What is the difference between alternator and Generator?

Ans. Both devices convert mechanical energy into electrical energy but the construction of both the devices is different. Generator consist stationary magnetic field and rotating conductor. It convert emf into DC current. While alternator has stationary armature and rotating magnetic field and it convert mechanical power into AC current.

Q.2 Why AC system is preferred over DC system?

Ans. Advantages are.

a. Easy transmission and distribution.

b. Cost of AC transmission is low and power losses are less.

c. AC is the basic produced current.

Q.3 What kinds of cables are used for power transmission?

Ans. 1 Low tension cables.

2. High tension cables

3. Super tension cables.

Q. 4 What is slip in an induction motor?

Ans. Slip is the difference between flux speed(Nx) and rotor speed (N). Rotor spee is always less then synchronous speed.

Q. 5 What is reliability?

Ans.It can be define as the capacity of the power system to withstand the load of the demand.

Q. 6 What is reverse power relay?

Ans. 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.

Q.7 Why is negative feedback more preferable in control system?

Ans. 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.

Q.8 What is hunting?

Ans. We come across the term HUNTING when we study about three phase synchronous motor operations. The word hunting is used because after sudden application of load the rotor has to search or hunt for its new equilibrium position. That phenomena is referred as hunting in synchronous motor.

Q.9 What is the significance of vector grouping in Power Transformers?

Ans. Every power transformer carries a vector group listed by its manufacturer. Fundamentally it tells you the information about how the windings are connected (delta or wye) and the phace difference betweent the current and voltage. EG. DYN11 means Delta primary, Wye Secondry and the current is at 11 o clock referred to the voltage.

Q.10 Why is negative feedback more preferable in control system?

Ans. 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.

Q. 1 What is maximum power theorem?

Ans. It explain about the total load that an resistance extract from the network. This include the maximum network power and in this case the load resistance is being equal to the network resistance.

Q. 2 How can you relate power engineering with electrical engineering?

Ans. Power engineering is the sub branch of electrical engineering. It consist with generation, transmission and distribution of electrical energy. All electrical equipment came under power engineering. Power engineering deals with the design and maintenance of electrical equipment.

Q. 3 What are the various cables used for transmissions of power?

Ans. 1 High tension cables ( 1000 volts)

2 Low tension cables ( 23000 volts)

3 Super tension cables ( 132 kv)

Q.4 What are the advantages of low power factors?

Ans. Line losses are 1.57 times unity power factor.

large generators and transformers are required.

Large conductor sized.

Low lagging power factors.

Q.5 What is reverse generating capacity?

Ans. Reverse generating capacity is the extra generating power for preventing maintenance.

Q.1 Why all domestic loads are inductive in nature?

Ans: In gen almost all the home appliances are made up of coil like things be it pump,light bulb ,motor etc tats why all the domestic loads are inductive.

Q.2 What is the cost ratio of refrigerated cooling(air conditioning) to evaporative cooling(desert coolers)

Ans: 8:1 , So the cost of cooling by air conditioner is 8 times then that required by standard desert cooler!

Q.3 Why all domestic loads are inductive in nature?

Ans: In gen almost all the home appliances are made up of coil like things be it pump,light bulb ,motor etc tats why all the domestic loads are inductive.

Q 4 What is the difference between generator and alternator?

Ans. In generator the magnetic field is stationary but the armature is rotating

While in alternator, the armature is stationary but the magnetic field is rotating.