Technical Interview: Electrical and Electronics Engineering: Questions

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Electrical and Electronics Engineering

1) Explain the working principle of a battery. List the batteries used in cell phones, laptops and electric vehicles with their Voltage ratings and operating characteristics.

2) Classify various types of storage cells. Explain the working principle of lead acid battery.

3) Define operating and restraining torques. Write the expression for operating and restraining torques of an admittance relay.

4) List the different protections used for motors. What is the main function of an overload protective device to protect the motors?

5) What is meant by single phasing? How to detect single phasing in a motor?

6) What are the effects of single phasing of a squirrel cage motor? During single phasing, maximum to nominal torque drops to.

7) Explain operation of balanced voltage longitudinal differential protection. Draw how the secondaries of CTs are connected in a balanced voltage longitudinal differential protection of transformer.

8) What are the required properties of CTs when using for indicating, metering and protection purpose?

9) What is meant by accuracy limit factor of current transformer? List out standard accuracy limiting factors.

10) Classify voltage transformers. List out the limits of errors in VT for measuring and protection purpose.

11) Draw the equivalent circuit diagram and vector diagram of potential transformer. Explain the causes of phase angle error and ratio error.

12) Define instrument security factor. Explain its significance.

13) What is meant by rated short time thermal current of a current transformer? List out the factors on which it depends.

14) Name different types of CTs used for protection and their purpose.

15) Define burden on CT and state the factors on which it depends.

16) What is the burden on the CT secondary with 1A compared to the CT with 5A secondary?

17) Explain the behavior of CT under transient fault condition. Explain the effect of CT saturation on impedance and overcurrent protection.

18) Explain the working principle of negative sequence relay. List out the functions of negative sequence current protection.

19) Difference between power transformer and distribution transformer. State the reasons for excessive flux densities in power transformers.

20) Explain how a thermal relay works. Draw thermal withstand curves for electric motor and thermal relay.

21) Explain the working principle of differential feeder protection scheme provides protection under double end power supply conditions?

22) Define a drive and state advantages of electric drive over other conventional drives.

23) Why do we need to consider rise in temperature in an electrical drive? What are the assumptions made for calculating rise in temperature in electrical drive systems?

24) Define a torque and differentiate between speed torque characteristics of single cage and double cage motors.

25) Draw the typical performance characteristics of LV induction motor. List out the factors affecting the losses.

26) What is meant by communication? Compare D. C. series motor and D. C shunt motor in terms of commutating properties.

27) Explain the working principle of linear motor and state its applications.

28) Explain the working principle of air blast circuit breaker. Explain why resistance switching is never used with air blast circuit breakers.

29) What will happen if secondary winding of current transformer is kept open? Explain the reasons for the cause.

30) Classify different types of measuring instruments based on working principles. Which of these principles is not used to design a wattmeter and which type of the instruments can՚t be used for the measurement of both D. C and A. C?

31) List out the methods used for testing cables for short circuits, ground faults and open circuits.

32) Classify null detectors and state the main features of electronic null detectors.

33) Why do we use bridge measurements? Explain how to reduce the errors due to thermal e. m. f in bridge measurements.

34) Why do we use arm ratios in bridge method of measurements? Explain how to decide the upper and lower limits for it.

35) Define installed capacity of a generating plant. What is the total installed electrical power generation capacity in India?

36) List the different standard voltages used for generation, transmission, and distribution systems.

37) What is the approximate useful life span of a transmission lines according to Indian standards?

38) Define load factor and state the order of normal residential or domestic load factor.

39) Explain the working principle of synchronous motor. Explain the effect of reversal of field current on the direction of rotation of the machine.

40) What is meant by plugging? Explain how plugging is done for synchronous motors.

41) Is the power developed in a salient pole machine is always greater than or lesser than the power developed by smooth rotor machine? Explain the reasons for it.

42) Define fractional pitch. Why do we prefer to have fractional pitch type of A. C machines?

43) Explain the working principle of repulsion motor. Explain what will happen if the load on a repulsion motor is increased beyond a certain value under which the reluctance torque cannot maintain the synchronous speed?

44) Out of synchronous machine, double cage induction machine, slip ring induction machine and D. C shunt machine, which machines is costlier for the same power output and state the reasons for it.

45) Explain the working principle of a D. C. motor. What will happen if A. C. supply is applied to D. C motor and explain the reasons for its effects?

46) How do you choose a rating of a pump? What eventually happen if we switch on a pump (introduction motor) with 25 % lower than its rated voltage?

47) What is the significance of reactive power in electrical power transmission system? Explain the methods used to inject the reactive power into transmission systems.

48) Classify electrical power transmission and distribution systems. What are the main criteria used for designing feeders and transmission lines?

49) Why do we need to maintain the power transmission system voltage within the limits? Where do we have to place, he booster transformers to increase/decrease the voltage in a transmission line?

50) Why and where do we prefer to use underground cabling? What is the general distance beyond which we don՚t prefer to go for underground cabling?

51) Define the zero-sequence impedance of a transformer. Draw zero sequence network circuits for different three phrase transformers connections.

52) Classify different protection schemes used for electrical distribution system & compare them.

53) List the methods of checking the instant of synchronization. What is the condition for maximum synchronization power in the parallel operation of alternators?

54) What is hydrograph and mass cure? Explain their importance.

55) Classify hydro turbines and draw the operating characteristics of water turbine.

56) What is the main function of turbine? Differentiate between impulse and reaction turbines.

57) Classify hydroelectric power plant. List out the factors on which the hydroelectric power plant output depends.

58) Explain the basic working principle of magneto hydro dynamic power generation.

59) What is an inter-connector? State the factors on which the power transmitted through the inter-connector depends.

60) What are the advantages of combined operation of power plants? Explain how reactive power is controlled in an inter-connected system.

61) State the necessary conditions for connecting alternators in parallel. Explain how the total KW load is divided between alternators connected in parallel.

62) What are the factors on which the amount of excitation of an alternator depends? Explain the effect of increasing the excitation of one of the alternators operating in parallel for sharing the load equally.

63) Explain the working principle of synchronous generator when it is operating under steady state, transient and sub-transient conditions.

64) Explain the effect of increasing the driving torque of one of the alternators operating in parallel.

65) Explain the effect of changing speed of one of the two alternators connected in parallel.

66) Explain the effects of varying the excitation of a synchronous machine connected to infinite busbars.

67) Explain the effects of varying the torque prime mover of the synchronous machine connected to infinite busbars.

68) Define synchronous capacity and short circuit ratio.

69) What is the condition for economical loading of alternators operating in parallel? Explain how is an alternator made to share the load after synchronizing?

70) Why do we use a synchroscope? Name the motor used in synchroscope.

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