Interview Questions

Electrical Interview Questions – Part 2

1. Why the capacitors works on ac only?

Generally, the capacitor provides infinite resistance to the DC components (ie, blocks the DC components). allows alternating current components to pass through.

2. Explain the working principal of the circuit breaker?

The circuit breaker is one that makes or breaks the circuit. It has two contacts, namely, fixed contact and mobile contact. Under normal conditions, the mobile contact comes into contact with the fixed contact, thus forming the closed contact for the current flow. During abnormal and defective conditions (when the current exceeds the nominal value), an arc occurs between the fixed and moving contacts and, therefore, forms the open circuit. The arc is extinguished by means of extinction of the arc such as air, oil, vacuum, etc.

3. How many types of colling system it transformers?

  • ONAN (oil natural,air natural)
  • ONAF (oil natural,air forced)
  • OFAF (oil forced,air forced)
  • ODWF (oil direct,water forced)
  • OFAN (oil forced,air forced)

4. What is the full form of KVAR?

We know that there are three types of electric power as active, apparent and reactive. Then KVAR is the support for Kilo Volt Amps with reactive component.

5. What is excitation?

Excitation is applying an external voltage to DC shunt coil in DC motors.

6. What is the function of interposing current transformer?

The main function of an interposing current transformer is to balance the currents supplied to the relay where otherwise there would be an imbalance due to the relationships of the main current transformers. The interposing current transformer is equipped with a wide range of taps that the user can select to achieve the required balance.

7. What is power quality meter?

Electrical quality meters are common in many industrial environments. Small units are now also available for domestic use. They provide operators with the ability to monitor the two disturbances in the power supply, as well as the energy used within a building or by a single machine or device. In some situations, the function and operation of the equipment are monitored and controlled from a remote location where communication is made through modem or high-speed communication lines

8. What is the main use of rotary phase converter?

The rotary phase converter will convert the single-phase power into a true balanced three-phase power, so it is often called a single-phase to three-phase converter. Often, the advantages of three-phase motors and other three-phase equipment make it worthwhile to convert single-phase 3-phase so that small and large consumers do not want to pay the additional cost of a 3-phase service, but still want to use 3 phases

9. What is meant by knee point voltage?

Knee point voltage is calculated for electrical Current transformers and is very important factor to choose a CT. It is the voltage at which a CT gets saturated. (CT‐current transformer).

10. What will happen if DC supply is given on the primary of a transformer?

Mainly the transformer has high inductance and low resistance. In the case of DC power supply, there is no inductance, only the resistance in the electrical circuit will act. So a high electric current will flow through the primary side of the transformer. So for this reason the coil and insulation are burned.

11. What is the difference between isolators and electrical circuit breakers?

The insulators are mainly for switching purposes under normal conditions, but they can not operate in fault conditions. Actually, they were used to isolate CBs for maintenance. Whereas CB is activated in fault conditions according to the detected fault

12. What are HRC fuses and where it is used?

The HRC represents the “high breaking capacity” fuse and is used in the distribution system for electrical transformers

13. what is stepper motor.what is its uses?

The stepper motor is the electric machine that acts on the input pulse applied to it. is a type of synchronous engine that runs in steps in any direction instead of running in full cycle. Therefore, in the automation parts it is used

14. What is SF6 Circuit Breaker?

SF6 is Sulpher hexa Flouride gas.. if this gas is used as arc quenching medium in a Circuitbreaker means SF6 CB.

15. what is meant by insulation voltage in cables? explain

It is the property of a cable that by virtue of being able to withstand the applied voltage without breaking, is known as the insulation level of the cable.

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