Interview Questions

60+ Interview questions for electrical engineers

1.How electronic regulator differs from ordinary rheostat regulator

Loss of power is very less while comparing the electronic regulator with an ordinary regulator and the reason for that is electronic regulator speed can be controlled so the needed power is used. In the case of an ordinary rheostat regulator, power wastage is equal for every speed so no power is saved.

2. Describe vacuum circuit breaker

A circuit breaker is a switching device and it can be operated manually and automatically. Protection of electrical system can be done by circuit breaker this type of circuit breaker is used for medium voltage. During a short circuit or overload, arc isolation is done in the system through the vacuum chamber.

3. What are the components of the load break switch

  • Potential transformer
  • Current transformer
  • Vacuum circuit breaker
  • Power fuse
  • Inverter
  • Anti-single phasing device
  • Arm lever for manual operation

4. Describe ATS

An automatic transfer switch is an electrical switch and it can transfer load from one source to another or it can also be described as it transfers power from normal to an emergency.

5. How a motor is affected by unbalanced voltage

Performance and the life of the motor would decrease. Current unbalance would happen if there is an unbalance in voltage at the motor stator terminals. Torque pulsation would happen because of the unbalanced current and also increases the mechanical stress and vibrations.

6. What are the types of electrical equipment in a substation

  • Power transformers
  • Instrument transformers
  • Conductors and insulators
  • Isolators
  • Bus bars
  • Lightning arresters
  • Circuit breakers
  • Relays
  • Capacitor banks and miscellaneous equipment

7. What is an electrical power transformer

With the help of a transformer, power transfer is done from one circuit to another. For the transmission and generation of power, this transformer would increase and decrease the voltage

8. Describe instrument transformers

The current and voltage transformer is an instrument transformer. Alternating current is measured by using the current transformer and it is done by taking samples of the higher currents of the system. The potential transformer takes samples of high voltages of a system to provide low voltage to the relays of the protection system.  

9. What is a bus bar

Bus bar can be described as a conductor that carries current and it has many incoming and outgoing line connections. Mostly substations have bus bars and it is divided into a single bus, ring bus, and double bus.

10. What is a one-line diagram

The one-line diagram can be explained as a simplified single-phase circuit diagram of a three-phase balanced electrical power system. A single line is used to indicate it and apparatus symbols are used. There are certain advantages for one line diagram they are simplicity, three phases of the balanced system is represented by one phase, and the circuit completion through the neutral is removed.

11. How to examine the electrical power system

The electrical power system must be safe and efficient. So in order to achieve this certain analyses must be done to design and operate a power system. Basic analysis of a power system can be done by

  • Power flow analysis
  • Fault analysis
  • Stability analysis

Power flow analysis is the major analysis in a power system. The fault could occur in a power system because of insulation failure in equipment, damage to conductors and tower, accidental faulty operation, and flashover of transmission lines by lightning stroke. Fault analysis would show the bus voltage and line current in case of faults. Stability analysis can be described as the ability of the machines in the system to remain in synchronism with one another during the faults and removal of the faults.

12. if any two phases in an induction motor are interchanged, then what will happen

The motor will run in the reverse direction

13  What is the primary and secondary transmission 

The transmission of power from the generation station to the substation is the primary transmission and the transmission would be done at high voltages in the range of 66kv-400kv. This will be supplied to the substation.

During secondary transmission, the primary voltage is reduced to low values of from 3.3KV – 33KV for secondary transmission.

14. Describe the merits of DC transmission

  • It only needs two conductors
  • There won’t be any problems related to inductance, capacitance, and phase displacement which we can see in AC transmission
  • Voltage drop is less for the same load and sending end voltage
  • There won’t be any system instability like AC transmission
  • For a DC transmission, there would be less corona loss and reduced interference with communication circuits

15. What are the required properties of the transmission line material

  • High electrical conductivity
  • Economical
  • Specific gravity must be low
  • Tensile strength must be high

16. What are the commonly used conductors

  • Copper
  • Aluminum
  • Galvanized steel
  • Cadmium copper

17. What are the requirements of transmission lines

  • Less transmission loss
  • It must deliver the power at a specified voltage
  • No radio interference
  • High availability

18. Explain medium and short line transmission

The range of medium transmission lines is from 50Km – 150Km and the line voltage in between 20KV-100KV. The long-distance transmission line is 150Km in length and it would carry higher voltage than 100KV.

19. Explain the short transmission line

If the length of the transmission line is up to 50Km, and the line voltage is lower than 20KV then it is a short transmission line.

20. Why do we use AC transmission instead of DC and what are its advantages

Voltage can be increased or decreased according to our need in AC power and that’s why we are using AC instead of DC. High voltage transmission of DC power would reduce power loss. AC power can be generated at high voltages because there is no commutation problem. 

21. How to do the transmission line voltage regulation

Certain methods can be used to control the voltage during transmission over long distances.

  • Use tap change transformers
  • Booster generators can be used
  • Shunt capacitors can be used at the receiving end during heavy loads or low power factors
  • Shunt reactors can be used during low loads to neutralize the effect of shunt capacitance of the long transmission lines

22. Which motor is an unexcited single-phase synchronous motor

Reluctance motor

23. The maximum power developed in the synchronous motor is depended upon

It is depended on the supply voltage for rotor excitation and coupling angle maximum value

24. What is the proximity effect

In the case of two ac carrying conductors which is nonparallel. Internal current in both the conductors gets rearranged in a way that the AC current density on the side nearer to the other conductor is lesser than that at the other end, and this is called proximity effect.

25. Why transformer cores are laminated

To minimize eddy current losses

26. Why do we connect the capacitor banks in series

The capacitor bank is connected in series so that the voltage at the load end can be improved in the transmission line. The voltage drop is high in a transmission line because of the impedance of the line. So to improve the voltage at the load terminals capacitor banks are used in series.

27. Explain the corona effect

Mostly corona would occur in high voltage transmission, the conductors that carry electric power at higher voltage have a strong electrostatic field around them and this would result in a violet visible discharge and it is called the corona. There would be humming sound in high voltage transmission line and this sound is due to the ionization of air around transmission conductor and this is called corona effect

28. What is the use of big rings at transmission line network or in substation

The metal ring that we see in this image is the corona ring, this ring is also installed in substations. In high voltage transmission networks, the corona discharge is very high. While using the corona ring it distributes the electrical potential gradient evenly and maintains the maximum value below the threshold limits of the corona effect. Corona rings are used at high altitude electrical equipment where the density of the air is less.

29. Why bundled conductors are used in extra high transmission line

In higher voltages, the chances of the corona are high, so bundled conductors are used in extra high voltage transmission lines to reduce the corona effect. Sub conductors have placed in a certain distance through-out the transmission line and this would reduce the corona discharge loss and interference with the communication lines nearby.

30. What are the factors that favor the corona

  • The tendency of the corona would be high during stormy weather
  • The conductors which have rough surface have more corona tendency
  • The tendency of the conductor would increase if the distance between the conductors are shorter
  • Chances of the corona are high in case of higher voltage

31. When will be the skin effect of the conductor will reduce

The skin effect of a conductor will reduce when the resistivity of conductor material increases.

32. The mechanical vibration produced by the laminations of a transformer depends on

  • Clamping tightness
  • The laminations gauge
  • size of laminations

33. Why no load on a transformer is carried out

It is carried out to determine magnetizing current and loss

34. Why sumpner’s test is carried out in transformers

It is carried out to determine the temperature of the transformer

35. What is the purpose of providing an iron core in a transformer

The reluctance of the magnetic path can be decreased by this

36. Explain switchyard

Switchyard can be considered as a junction where the transmission of power takes place. A power plant can be secured by switchyard and it also helps in the transmission of power.

Switchyard links the generation plant and transmission system, the switchyard is considered as a switching station it is the heart of power plant. Reactive power devices are controlled by switchyard.

37. What is the equipment in a switchyard

  •  Current and voltage transformer
  • Lightning arrestor
  • Power transformers and isolators
  • Bus bar and circuit breaker
  • Earthing switch and wave trap

38. What are the protection system elements in an electrical system

  • Protective relays
  • Circuit breakers
  • Current and voltage transducers
  • Communication channels
  • DC supply system and control cables

39. How can relays detect faults

During a fault condition the voltage, current, and frequency would behave in a peculiar way. Relays are able to measure the current and voltage and know the changes in current and voltage. Relays can detect if there is an overcurrent or under-voltage case and it also has many other methods of detection.

40. Explain circuit breaker

The circuit breaker can be considered as an automatically operated electrical switch, which is designed to protect electrical circuits from damages such as overload or short circuits. There are different types of circuit breakers with different sizes. Circuit breakers are mostly arranged with pilot devices so that fault current can be sensed.

If the circuit breaker detects the fault, contacts within the circuit breaker will open to interrupt the circuit. Mechanically stored energy in the breaker is used to separate the contacts

41. Why electrical clearance is needed

Electrical is needed to provide the physical separation required for the phase to phase, phase to structure, and phase to ground. Air gaps are to provide a safe working area and to prevent flashovers.

42. What is short circuit force

Short circuit forces are structure loads, which is caused by circuit current

43. What will happen to the power factor of the synchronous motor if the excitation current is increased

Power factor will improve

44. What will happen to the PF of the synchronous motor, if the field of the synchronous motor is under-excited

Power factor will be lagging

45. In a transmission system, the receiving end voltage can be maintained close to sending end voltage by using

Static or synchronous condensers

46. For what purpose do we use batteries in a power substation

Batteries are used in a power substation to operate the trip circuit

47. For which type of transmission lines does the MHO relay is used

They are used for long lengths

48. What are the types of relay that are used for the protection of apparatus and transmission lines  

  • Over-current and directional relay
  • Distance and under-voltage relay
  • Thermal and under-frequency relay
  • Differential and pilot relay
  • Phase sequence relays

49. Why the efficiency of the induction motor is less when compared to the transformer

The working principle of the transformer and an induction motor is the same which is mutual induction. In the case of the transformer, the flux will travel from primary to secondary winding through the core of the transformer, while in case of induction motor the flux travels from stator to rotor through the air gap. So the power factor of the induction motor will be less when compared to the transformer.

50. What is islanding operation in the electrical grid

If the frequency of the electrical grid is declined below the rated pre-determined frequency, then the electrical grid would be divided into a number of small islands that have some generation units and load centers. The method of splitting the electrical grid into a small part is to protect the healthy part of the grid.

51. What is the disadvantage of constant voltage transmission

The system short circuit current will increase

52. The surge impedance for the overhead line is

100-200 ohms

53. What are the different type of test conducted on a transformer

A polarity test is done to know the relative polarity of the primary and secondary terminals so that the windings of the transformer can be connected in parallel.

Open circuit test, this test is also known as the no-load test and this will help to determine the core losses in the transformer.

By doing a short circuit test we could know the full load copper loss in the transformer.

Sumpner’s test is carried out to know the temperature rise in the transformer

54. What are the types of faults that could occur in a power system

Phase faults

Phase faults are phase to ground faults, phase to phase fault, phase – phase to ground fault, and three-phase fault

Open circuit faults – Mostly open circuit faults are occurred by overhead line parting or by the pole of circuit breaker not fully closing.

Inter turn faults – The inter-turn faults, mostly occurs in transformers, generators, and motors. This could occur due to the insulation breakdown between the turns of the same phase or between the parallel winding.

Over-load faults can occur due to exceeding the maximum permissible load currents through the windings, cables, or transmission line

55. What type of insulators are used in 220KV transmission lines

Suspension type

56. In a transmission line where grounding is done

At the supply end

57. Why thermal protection switch is used in the power line system

It is used as a protection against overload.

58. Where the earthing switch is generally installed

It is generally installed on circuit breaker frame

59. In a transmission line which wire is above all the other wire

Earth wire

60. What is the advantage of transmitting power at high voltage

Size of the conductor is reduced

61. What are the advantages of an overhead distribution system over underground distribution system

The initial cost will be less and they are easy to repair in case of any faults

62. What will happen if the voltage and P.F in a transmission system increases

The efficiency of transmission will increase

63. How can we improve the power factor of a factory

It can be improved by installing shunt capacitors near the load

80+ Electrical interview questions


post-graduate in Electronics & communication.

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