Sample Questions on Diploma Electrical Engineering

1. The advantage of transmitting power at high voltage is
(a) magnitude of current will be small
(b) it will reduce the voltage drop in the line
(c) power loss will be less
(d) all of these

2. In the protection scheme, relay functions as a
(a) switching device
(b) sensing device
(c) breaking device
(d) none of these

3. The most common type of fault is
(a) single-phase to ground
(b) phase-to-phase
(c) two-phase to ground
(d) three-phase to ground

4. HVDC transmission is mainly used for
(a) bulk power transmission over very long distances
(b) interconnecting two systems with the same nominal frequency
(c) eliminating reactive power requirement in the operation
(d) minimizing harmonics at the converter stations

5. The transfer function of a tachometer is of the form
(a) KS
(b) k/s
(c) k/(S+1)
(d) k/S(S+1)

6. In a speed control system, output rate feedback is used to
(a) Limit the speed of motor.
(b) Limit the acceleration of the motor.
(c) Reduce the damping of the system.
(d) Increase the gain margin.

7. A phase-lag compensator will
(a) improve relative stability
(b) increase the speed of response
(c) increase bandwidth
(d) increase overshoot

8. If the armature current is increased to double its previous value, and the time of commutation is halved, how will the reactance voltage vary?
(a) It will be halved
(b) It will remain the same
(c) It will be doubled
(d) It will become four times

9. Synchronous generators used in thermal power plants have
(a) Cylindrical rotors
(b) Salient pole rotors
(c) Stator slots in multiple of 6
(d) All of these

10. How can the reactive power delivered by a synchronous generator be controlled?
(a) By changing the prime mover input
(b) By changing the excitation
(c) By changing the direction of rotation
(d) By changing the prime mover speed

11. A cylindrical rotor synchronous motor with damper windings is switched on without dc supply to its field windings. It will
(a) not start
(b) start but not run at synchronous speed
(c) start as an induction motor and then run as a synchronous motor
(d) start and run as a synchronous motor

12. In hand tool applications, which of the following single–phase motor is used?
(a) Shaded pole motor
(b) Capacitor start motor
(c) Capacitor run motor
(d) Universal motor

13. Bundled conductors in EHV transmission lines results in
(a) Reduced capacitance
(b) Increased capacitance
(c) Increased inductance
(d) Decreased inductance

14. The rating of a 3–phase power system is given as
(a) rms phase voltage
(b) peak phase voltage
(c) rms line to line voltage
(d) peak line to line voltage

15. HVDC transmission lines are more economical for
(a) Short distance transmission
(b) Long distance transmission
(c) Any distance transmission
(d) Interconnected systems

16. Which of the following compensations is adopted for improving transient response of a negative unity feedback system?
(a) Phase lead compensation
(b) Phase lag compensation
(c) Gain compensation
(d) Both (b) and (c)

17. A negative sequence relay is commonly used to protect
(a) An alternator
(b) A transformer
(c) A transmission line
(d) A bus bar

18. For a single-phase capacitor start induction motor, which of the following statements is valid?
(a) The capacitor is used for power factor improvement.
(b) The direction of rotation can be changed by reversing the main winding terminals.
(c) The direction of rotation cannot be changed.
(d) The direction of rotation can be changed by interchanging the supply terminals.

19. Which three-phase connection can be used in a transformer to introduce a phase difference of 30° between its output and corresponding input time voltages?
(a) Star-Star
(b) Star-Delta
(c) Delta-Delta
(d) Delta-Zigzag

20. Which of the following motors definitely has a permanent magnet rotor?
(a) DC commutator motor
(b) Brushless DC motor
(c) Stepper motor
(d) Reluctance motor

21. The phase sequence of a three phase alternator will reverse if
(a) The field current is reversed keeping the direction of rotation same
(b) The field current remains the same but the direction of rotation is reversed
(c) The field current is reversed and the number of poles is doubled
(d) The number of poles is doubled without reversing the field current

22. The dc motor, which can provide zero speed regulation at full load without any controller is
(a) Series
(b) Shunt
(c) cumulative compound
(d) differential compound

23. Shunt reactors are sometimes used in high voltage transmission system to
(a) limit the short circuit current through the line.
(b) compensate for the series reactance of the line under heavily loaded condition.
(c) limit over-voltages at the load side under lightly loaded condition.
(d) compensate for the voltage drop in the line under heavily loaded condition.

24. MHO relay is normally used for protection of
(a) Short line
(b) Long line
(c) Medium line
(d) None of these

25. A Buchholz relay is used for
(a) Protection of induction motor
(b) Protection of synchronous motor
(c) Protection of transformer against external fault
(d) Protection of transformer against internal fault

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26. The insulation of modern EHV is designed based on
(a) Lightening voltage
(b) Switching voltage
(c) Corona voltage
(d) Radio Interference

27. Which of the following circuit breakers produce least arc energy?
(a) Air circuit breaker
(b) Oil circuit breaker
(c) Vacuum circuit breaker
(d) Air blast circuit breaker

28. The basic function of a transformer is to change
(a) The power level
(b) Voltage level
(c) Power factor
(d) Frequency

29. A negative feedback closed loop system is supplied to an input of 5 volt. The system has a forward gain of 1 and a feedback gain of 1. What is the output voltage?
(a) 1.0 V
(b) 2.5 V
(c) 1.5 V
(d) 2.0 V

30. Time response for a second order system depends on value of æ. If æ = 0 then the system is called as
(a) Un-damped system
(b) Under damped system
(c) Critically damped system
(d) Over damped system

31. The function of commutator in a d.c. generator is
(a) to collect current from armature conductors
(b) to improve commutation
(c) to conduct current to the brushes
(d) to change a.c. to d.c.

32. The function of starter in d.c. motors is
(a) to avoid excessive current at starting
(b) to control the speed
(c) to avoid armature reaction
(d) to avoid excessive heating

33. The efficiency of a d.c. machine is maximum when
(a) the machine is running at full-load
(b) the machine is running at no-load
(c) the variable loss equals the constant loss
(d) none of these

34. Which motor can conveniently operate at lagging as well as leading power factor?
(a) squirrel-cage induction motor
(b) wound-rotor induction motor
(c) synchronous motor
(d) d.c. shunt motor

35. Which portion of the power system is more prone to faults?
(a) Alternators
(b) Transformers
(c) Overhead lines
(d) Underground cables

36. Salient pole type rotors are generally used with prime movers of
(a) high speed
(b) low speed
(c) medium speed
(d) both high and low speed

37. In an npn transistor, the majority carriers in the emitter are
(a) free electrons
(b) holes
(c) neither
(d) both

38. Transistor is a
(a) current controlled current device
(b) current controlled voltage device
(c) voltage controlled voltage device
(d) voltage controlled current device

39. Zener diodes are commonly used as
(a) Rectifiers
(b) voltage regulators
(c) amplifiers
(d) none of these

40. Which of the following transistor configurations has the highest power gain?
(a) common base
(b) common emitter
(c) common collector
(d) none of these

41. The number of diodes required in a bridge rectifier circuit is
(a) One
(b) Two
(c) Three
(d) four

42. Out of the following devices, the fastest switching device is
(a) JFET
(b) BJT
(d) triode

43. Thyristor is nothing but a
(a) controlled switch
(b) controlled transistor
(c) amplifier with large current rating
(d) amplifier with higher gain

44. The output of a 2-input OR gate is zero only when
(a) both inputs are 0
(b) either input is 0
(c) both inputs are 1
(d) either input is 1

45. Which logic gates are designated as universal gates?
(a) NOT, OR and AND gates
(b) XNOR, NOR and NAND gates
(c) NOR and NAND gates
(d) XOR, NOR and NAND gates

46. The basic elements of a microprocessor are
(a) ALU and memory
(b) ALU and control unit
(c) ALU, memory and I/O devices
(d) ALU, control unit and memory

47. In microprocessor architecture, flag indicates
(a) the number of the microprocessor
(b) the name of the manufacturer
(c) the internal status of the CPU
(d) the bit size of the microprocessor

48. A modulator is a system to
(a) separate two frequencies
(b) impress the information on to a radio frequency carrier
(c) extract information from the carrier
(d) amplify the audio frequency signal

49. The main purpose of modulation is to
(a) combine two waves of different frequencies
(b) achieve wave-shaping of the carrier wave
(c) transmit low-frequency information over long distances efficiently
(d) produce sidebands

50. The most useful modulation technique for high fidelity audio broadcasting on radio in current practice is
(a) amplitude modulation
(b) frequency modulation
(c) pulse amplitude modulation
(d) pulse code modulation