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Thursday, July 28, 2011

Objective electrical engineering solved question papers

Objective electrical engineering solved question papers
Electrical Engineering objective questions MCQ
Electrical Engineering Solved Sample Questions

1. A single-phase induction on motor with only the main winding excited would produce zero torque at
(a) synchronous speed only
(b) starting and synchronous speed
(c) starting only
(d) starting and a speed slightly below synchronous speed

Ans:-B


2. A polyphase slip-ring induction machine has the stator and rotor windings wound for
(a) the same number of phase 6ut different number of pairs of poles
(b) the same number of pairs of poles but different number of phases
(c) the same number of phases with number of pairs of poles either equal or different
(d) the same number of pairs of poles with number of phases either equal or different

Ans:-D


3. The single-phase Induction motor is started with
(a) capacitance connection
(b) inductance connection
(c) resistance connection
(d) shaded pole arrangement

Ans:-A




4. Low voltage starting of induction motors is prescribed because
(a) high starting current at full voltage would damage the windings
(b) it facilitates smooth acceleration.
(c) it increases the life of the motor.
(d) it is mandated by electric supply authorities to prevent voltage dips at other consumer premises.

Ans:-A



5. The leakage flux in a transformer depends upon the
(a) applied voltage
(b) frequency
(c) load current
(d) mutual flux

Ans:-C


6. The voltage regulation of a large transformer is mainly influenced by
(a) no-load current and load power factor
(b) winding resistances and load power factor
(c) leakage fluxes and load power factor
(d) winding resistances and core loss

Ans:-C



7. The following lists relate to speed control of dc motors. Match List I with List II, and select the correct answer using the codes given below the lists:
List I
A. Armature voltage control
B. Field current control
C. Use of diverter resistance
D. Rheostatic control
List II
1. Speeds above base speed
2. Speeds below base speed
3. Poor motor efficiency
4. Speed control of series motor
Codes:
A B C D
(a) 1 2 3 4
(b) 2 1 4 3
(c) 4 1 3 2
(d) 2 3 1 4

Ans:-B

8. In a line printer used to print the output of a computer, the paper is required to be advanced by line spacing as soon as printing of the line is over. Which one of the following motors is best suited for this application?
(a) DC motor
(b) Synchronous motor
(c) Induction motor
(d) Stepper motor

Ans:-D


9. While plugging a 3-phase Induction motor, one supply terminal gets disconnected, then the motor will
(a) Continue to run in the same direction
(b) stop
(c) start rotating in the opposite direction at the same speed
(d) start rotating in the opposite direction at reduced speed

Ans:-A





10. The inductance of a three-phase transmission line is 1.2 mH /phase/km. If the spacing of conductors and the radius of the conductor are doubled, then the Inductance of Ike line will be
(a) 4.8 mH /phase/km
(b) 1.2 mH /phase/km
(c) (In 2) x 1.2 mH /phase/km
(d) (In 4) x 1.2 mH /phase/km

Ans:-B

11. A three-phase transmission line of negligible resistance and capacitance has an inductive reactance of 100 ohms per phase. When the sending-end and receiving-end voltages are maintained at 110 kV, the maximum power that can be transmitted will be
(a) 121MW
(b) 121/3 MW
(c) 363 MW
(d) 363 kW

Ans:-A


12. The surge impedance of a 100 km long underground cable is 50 ohms. The surge impedance of a 40 km long similar cable would be
(a) 20 ohms
(b) 50 ohms
(c) 80 ohms
(d) 125 ohms

Ans:-B

13. A string insulator has 4 units. The voltage across the bottom-most unit is 33.33% of the total voltage. Its string efficiency is
(a) 25%
(b) 33.33%
(c) 66.67%
(d) 75%

Ans:-D


14. The design of insulation for systems above 400 kV, is based upon
(a) lightning over voltage
(b) switching surges
(c) system voltage level
(d) system load level

Ans:-B

15. Bundled conductors in EHV transmission systems provide
(a) increased line reactance
(b) reduced line capacitance
(c) reduced voltage gradient
(d) increased corona loss

Ans:-C

16. A power system is subjected to a fault which makes the zero sequence component of current equal to zero. The nature of fault is
(a) double line to ground fault
(b) double line fault
(c) line of ground fault
(d) three-phase to ground fault

Ans:-B


17. For which of the following reasons is a differential relay biased to avoid maloperation when used for transformer protection?
(a) Saturation of CT’s
(b) Mismatch to CT ratios
(c) Difference in connection of both sides
(d) Current setting multiplier
Select the correct answer using the codes given below:
Codes:
(a) l and 4
(b) l and 2
(c) 2, 3 and 4
(d) 1, 2 and 3

Ans:-D

18. Protection scheme used for detection of loss of excitation of a very large generating unit feeding power into a grid employs
(a) under voltage relay
(b) offset mho relay
(c) under frequency relay
(d) percentage differential relay

Ans:-B


19. Which one of the following is not true regarding HVDC transmission?
(a) Corona loss is much more in HVDC transmission.
(b) The power transmission capability of bipolar line is almost the same as that of signal circuit ac line
(c) HVDC link can operate between two ac systems whose frequencies need not be equal
(d) There is no distance limitation for HVDC transmission by underground cable

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 if the Assertion A and the Reason R is individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answer to these items using the codes given below and mark your answer sheet accordingly.
Codes:
(a) Both A and R is true and R is the correct explanation of A
(b) Both A and R is 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

20. Assertion (A) : In three-phase star connected network, the neutral point can assume any potential upto phase voltage.
Reason (R) : The three-phase voltage system is unbalanced. The three voltages are not equal in magnitude but they are displaced by 1200.

Ans:-A

21. Assertion (A) : In a balanced three-phase star connected system, the line voltage is equal to 1.732 times the phase voltage.
Reason (R) : The line voltage is the vector sum of the two phase voltages.

Ans:-C


22. Assertion (A): Linearity is essential for the servo amplifiers.
Reason (R) : The servo amplifiers are used to amplify’ the output of the null detector.

Ans:-B


23. Assertion (A): The sampling period of a sampled data system must be ≤ 0.5 s to have a bandwidth ≤ 6.28 rad/s.
Reason (R): The signal is fully preserved in the sampled version so long as the sampling frequency is at least twice the maximum frequency contained in the signal.

Ans:-A

24. Assertion (A): For High-Q coils, inductance measurement is better done with Hay’s Bridge rather than with Maxwell’s Bridge.
Reason (R): Hay’s Bridge uses the standard capacitor in series with a variable resistor while Maxwell’s Bridge uses it in parallel.

Ans:-A

25. Assertion (A): Self-biasing method of biasing is generally used for a CE amplifier. Reason (R): The design of self-biasing circuit is very easy as compared to other biasing circuits.

Ans:-A


26. Assertion (A): In analog computation only summing amplifiers and integrators are used.
Reason (R): The differentiators using operational amplifiers cannot be designed.

Ans:-A

27. Assertion (A): In a salient pole 3-phase alternator, direct axis synchronous reactance is more than the quadrature axis synchronous reactance.
Reason (R): The length of air-gap along the direct axis of the salient pole 3-phase alternator is less than that along quadrature axis.

Ans:-A

28. Assertion (A): Adaptive delta modulation circuit has less distortion.
Reason (R): Quantisation noise is reduced.

Ans:-A


29. Assertion (A): A phase controlled line commutated converter can be operated both as rectifier and invertors.
Reason (R): S.C.R.’s have the property of blocking positive as well as negative voltages and they can be made conducting whenever required during the positive half cycle.

Ans:-C


30. Assertion (A) : In the nominal — π model of an overhead transmission line, the value of the sending-end voltage obtained for the normal rated load at the receiving-end at rated voltage, is higher than the actual value.
Reason (R): The nominal — π method underemphasize the effect of line capacitance giving a higher value of the sending-end voltage than the actual.

Ans:-C

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