electrical engineering test questions

electrical engineering test questions
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Electrical Engineering Technical Test Questions

1. Consider the following statements:
1. Reduce fault level
2. Improve stability of the system
3. Achieve asynchronous operation
Among these statements:
(a) 1 and 2 are correct
(b) 2 and 3 are correct
(c) 1 and 3 are correct
(d) 1, 2 and 3 are correct

Ans:-B

2. Consider the following statements regarding stability analysis by Routh-Hurwitz criterion:
1. For a system to be stable, all the coefficients of the characteristic equation must be present and be of the same sign.
2. If a system is to be stable, there should not be any sign change in the first column of the Routh‘s array.
3. The order of the auxiliary equation obtained from the elements of the Routh‘s table is always odd.
Of these statements:
(a) 1 and 2 are correct
(b) 2 and 3 are correct
(c) 1 and 3 are correct
(d) 1, 2 and 3 are correct

Ans:-A
3. A synchro transmitter-control transformer pair is excited at 400 Hz ac voltage. The output voltage
(a) has constant magnitude but its phase angle is proportional to the angular difference between their rotor angles
(b) Has a magnitude proportional to the sine of the angular difference between their rotors with its phase angle changing by 180° whenever the sign of the angular difference changes
(c) Has both magnitude and phase angle proportional to the angular difference between their rotors
(d) Has constant magnitude but its phase angle changes by 180° whenever the sign of the angular difference changes

Ans:-B


4. To ensure that a two-phase induction type servomotor does not run when the control phase voltage is zero, the ratio of
(a) Stator leakage reactance to rotor phase resistance should be high
(b) Rotor leakage reactance to rotor phase resistance should be less than one
(c) The sum of stator and rotor resistances to the sum of stator and rotor leakage reactances should be greater than one
(d) Torque to inertia should be very high

Ans:-B

5. A 1000/5 A bar primary current transformer has the ratio and phase errors at its rated current with a certain secondary burden of — 0.24 per cent and +30 minutes respectively. If the number of secondary turns is reduced by unity, the new ratio error and phase error at the rated current and for the same burden will be respectively
(a) —0.24 per cent and + 30 minutes
(b) + 0.26 per cent and + 30 minutes
(c) + 0.24 per cent and — 30 minutes
(d) zero and + 30 minutes

Ans:-A

Directions: The following items consist of two statements, one labelled the “Assertion A” and the other labelled the ‘Reason R’. You are to examine these two statements carefully and decide f the Assertion A and the Reason R are individually true and f so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below and mark your answer sheet accordingly.
Codes:
(a) Both A and R are true and R is the correct explanation of A
(b) both A and R are true but R Is NOT a correct explanation of A
(c) A is true but R is false
(d) A is false but R is true



6. Assertion (A): The generated voltage in three- phase supply contains harmonics.
Reason (R): The angular variation of the radial component of the magnetic flux in the air-gap is not a pure sinusoid.

Ans:-A

7. Assertion (A): The driving-point impedance and the driving-point admittance are reciprocals of each-other.
Reason (R) : The driving-point network functions are the ratios of Laplace transforms of appropriate quantities (voltage and current) at the same pair of terminals.

Ans:-A

8. Assertion (A): In the case of wave-type winding in a dc machine of more than two poles, two brushes may be just enough for communication, but the normal practice is to use as any brushes as there are poles in the machine.
Reason (R): On using more than two brushes in a 4-pole machine, the number of coils in series undergoing communication becomes half and so also the emf of self-induction in the commutated coils.

Ans:-C

9. The economizer, a component of steam power plants, is a heat-exchanger utilizing the waste heat of
(a) bleed-steam to heat the feed water
(b) flue-gas to heat the feed water
(c) flue-gas to heat the air going into the boiler
(d) flue-gas to heat the pulverised coal

Ans:-B

10. Consider the following statements about the utility of delta-connected tertiary windings in star-star connected power transformer:
1. It makes supply available for small loads.
2. It provides low reactance paths for zero sequence currents.
3. It is used to suppress harmonic voltages.
4. It is used to allow flow of earth fault current for operation of protective relays.
Which of these statements are correct?
(a) 1 and 2
(b) 2, 3 and 4
(c) 1, 3 and 4
(d) 1, 2, 3 and 4

Ans:-D

11. A 3-phase transmission line conductors were arranged in horizontal spacing, with ‘d’ as the distance between adjacent conductors. If these conductors are rearranged to form an equilateral triangle with sides equal to‘d’, then the
(a) capacitance and the inductance will increase
(b) capacitance will increase and the inductance will decrease
(c) capacitance and the inductance will remain the same
(d) capacitance will decrease and the inductance will increase

Ans:-B


12. The Inductance per unit length of an overhead line due to internal flux linkages
(a) depends on the size of the conductor
(b) is independent of the size of conductor and constant
(c) depends on the current through the conductor
(d) depends on distance between conductors

Ans:-B

13. A synchronous generator with a synchronous reactance of 1.3 Pu is connected to an infinite bus whose voltage is I pu, through an equivalent reactance of 0.2pu. For maximum output of 1.2 pu, the alternator emf must be
(a) 1.5pu
(b) 1.56pu
(c) 1.8 pu
(d) 2.5pu

Ans:-A

14. Consider the following statements:
Transient stability of a synchronous generator feeding power to an Infinite bus through a transmission line can be increased by
1. increasing the steam supply to the turbine driving the generator during fault clearing.
2. connecting resistors at the generator terminals during fault conditions.
3. employing a faster excitation system.
4. quickly throwing off the generator load.
Which of these statements are correct?
(a) 2 and 3
(b) 3 and 4
(c) l and 2
(d) 2 and 4

Ans:-D


15. An overhead transmission line having surge impedance ‘Z1 ‘is terminated to an underg1ound cable of surge impedance ‘Z2’ The reflection coefficient for the travelling wave at the junction of the line and cable is
(a) ZI +Z2 / Z1 -Z2
(b) Z2 / Z1 + Z2
(c) Z2 – Z1 / Z1 +Z2
(d) Z1 – Z2 / Z1 +Z2

Ans:-C


16. Ring main distribution is preferred to a radial system because
(a) voltage drop in the feeder is less and supply is more reliable
(b) voltage-drop in the feeder is less and power factor is high
(c) power factor is high and supply is more reliable’
(d) power factor is high and system is less expensive

Ans:-A

17. If the fault current is 3000 A for a relay with a plug setting of 50% and CT ratio of 1000:1, the plug setting multiplier would be
(a) 1.5
(b) 3
(c) 4.5
(d) 6

Ans:-D

18. Match List I (Protective schemes) with List II (Equipment) and select the correct answer using the codes given the Lists:
List I
A. Mho relays
B. Inverse time over current relays
C. Differential relays
List II
1. Generators
2. Transmission lines
3. Motors
Codes:
A B C
(a) 2 1 3
(b) 2 3 1
(c) 3 2 1
(d) 1 3 2

Ans:-C

19. Reversal of power flow In HVDC link by controlling the firing angle simultaneously at both the converter stations results in
(a) reversal of voltage polarity of HVDC pole
(b) reversal of current in dc link
(c) reversal of current in dc link as well as reversal of voltage polarity of HVDC pole
(d) neither reversal of current in dc link nor reversal of voltage polarity of HVDC

Ans:-B
20. In a loaded dc generator, if the brushes are given a shift from the interpolar axis in the direction of rotation, then the commutation will
(a) improve with fall of terminal voltage
(b) deteriorate with fall of terminal voltage
(c) improve with rise in terminal voltage
(d) deteriorate with rise in terminal voltage

Ans:-B
21. A dc shunt motor is required to drive a constant power load at rated speed while drawing rated armature current. Neglecting saturation and all machine losses, f both the terminal voltage and the field current of the machine are halved, then
(a) the speed becomes 2 pu (per unit) but armature current remains at 1 Pu
(b) the speed remains at 1 Pu but armature current becomes 2 Pu
(c) both speed and armature current becomes 2 Pu
(d) both speed and armature current remain at 1 pu

Ans:-B

22. A 3-phase synchronous motor with negligible losses is connected to the supply at rated frequency and constant terminal voltage ‘V’ The induced emf of the motor is designated as E. If the motor is now gradually loaded to its rated power, adjusting its excitation to obtain, say 0.8 leading power factor operations, then E-phasor would
(a) be less than V-phasor and also lead V-phasor
(b) be greater than V-phasor and also lead V-phasor
(c) be less than V-phasor and also lag V-phasor
(d) be greater than V-phasor and also lag V- phasor

Ans:-A
23. An alternator of 400 kW is driven by a prime mover of speed regulation 4% and another alternator of 200 km is driven by a prime mover of speed regulation 3%. The total load they can machines is
(a) 600 kW
(b) 500 kW
(c) 450 kW
(d) 400 kW

Ans:-C


24. Consider the following statements:
Modern alternators are designed for large air- gap to have
1. large inherent regulation.
2. very stable parallel operation.
3. higher stability limit
4. sinusoidal mmf distribution.
Which of these statements are correct?
(a) 1, 2 and 3
(b) 2, 3 and 4
(c) 1, 3 and 4
(d) 1, 2 and 4

Ans:-B


25. When a single-phase capacitor start induction motor is running at a steady speed delivering a fixed torque, then
(a) peak of forward rotor mmf is equal to the peak of backward rotor mmf
(b) peak of forward stator mmf is equal to the peak of backward stator mmf
(c) net forward rotating flux is equal to the net backward rotating flux
(d) forward flux produced by rotor current is equal to backward flux produced by rotor current

Ans:-C