Switchgear and Protection Mcq with Answers

1. In ac distribution system the voltage can be controlled by using

(a) tap changing transformer.
(b) booster transformer
(c) induction regulator.
(d) any of the above.

2. Tap changing transformers are employed for

(a) stepping down the voltage.
(b) stepping up the voltage.
(c) supplying low voltage current to instruments.
(d) both stepping up and stepping down the voltage.

3. The best location for use of a booster transformer in a transmission line is

(a) at the sending end.
(b) at the receiving end.
(c) at the intermediate point.
(d) any where in the line.

4. For voltage control in ac distribution system the induction regulators have the advantage(s) of

(a) reliability of operation.
(b) operation independent of load and power factor variations.
(c) stepless voltage variations without acing or short-circuiting of turns as in the case of transformers.
(d) all of the above.

5. A line voltage regulator is to be used in a single phase 200 V, 5 kVA system to keep the voltage constant for voltage variations within ± 10%. The rating (in kVA) of the voltage regulator is

(a) 0.05
(b) 0.5
(c) 5
(d) 50

4. Series capacitor is used in a transmission line to

(a) compensate the voltage drop.
(b) reduce line losses.
(c) limit short-circuit current.
(d) improve load power factor.

5. Shunt compensation in an EHV line is used to improve

(a) stability and fault level.
(b) fault level and voltage profile.
(c) voltage profile and stability.
(d) stability, fault level and voltage profile.

6. …………are used to provide compensation at the receiving end of a transmission line so as to improve its voltage profile.

(a) Condensers.
(b) Resistors.
(c) Reactors.
(d) Condensers, resistors or reactors.

7. The combined effect of series and shunt compensation on transmission lines in terms of degree of series compensation (K_se), degree of shunt compensation (K_sh), and surge impedance of uncompensated line (Z_o) is given by which one of the following equations ?

(a) Z’_o = Z_o √(1 – K_se).√(1 – K_sh)
(b) Z’_o = [√(1 – K_se).√(1 – K_sh)] ÷Z_o
(c) Z’_o = Z_o[(1 – K_se)÷(1 – K_sh)]^1/2
(d) Z’_o = Z_o[(1 – K_sh)÷(1 – K_se)]^1/2

8. Consider the following statements : Addition of lumped capacitances in parallel to a loss-free transmission line increases

1. characteristic impedance.
2. propagation constant.
3. system stability.
4. charging current.

Which of these statements are correct ?
(a) 1 and 3
(b) 2 and 4
(c) 2, 3 and 4
(d) 1, 2 and 4

9. What will happen if a short-circuit fault occurs in a switched capacitor controlled reactor?

(a) Oscillation.
(b) Capacitor discharge.
(c) Over voltage.
(d) Noise.

10. An AC capacitor is to be switched in parallel with AC line using back to back connected thyristor. What is the firing angle of thyristor for first switching?

(a) 0°
(b) 180°
(c) 90°
(d) 45°

11. Which of the following is provided with arcing horns?

(a) Isolator.
(b) Air-break switch.
(c) Oil switch.
(d) None of the above.

12. Pole mounted substations are used in

(a) primary transmission system.
(b) secondary transmission system.
(c) primary distribution system.
(d) secondary distribution system.

13. With large reactance interconnector between two power stations

(a) the power stations may fall out of step due to large angular displacement between the power stations.
(b) power will be transferred with minimum power losses.
(c) power will be transferred with voltage fluctuations and noise.
(d) none of the above.

14. AC network analyzer is employed for solving the problems of

(a) load flow.
(b) load flow and stability.
(c) load flow and short circuit.
(d) load flow, stability and short circuit.

15. Consider the following statements : Stability studies constitute

1. the major analytical approach to the study of power system electromechanical dynamic behavior.
2. the involvement of one or just a few machines undergoing slow or gradual changes in operating conditions.
3. the determination of the locus of essentially steady-state operating points of the system.
4. the determination of whether or not the rotors of the machines being perturbed, return to the constant speed operation. Which of the statements given above are correct ?

(a) 1, 2 and 3.
(b) 2, 3 and 4.
(c) 1 and 4.
(d) 1, 2, 3 and 4.

16. Power system stability is defined as

(a) that attribute of the system or part of the system which enables it to develop restoring forces between the elements there of equal or greater than disturbing forces so as to restore a state of equilibrium between the elements.
(b) the maximum power flow possible through some particular point in the system when the entire or part of the system is disturbed.
(c) both (a) and (b).
(d) neither (a) nor (b).

17. Stability limit of a power system is defined as

(a) that attribute of the system or part of the system which enables it to develop restoring forces between the elements there of equal or greater than disturbing forces so as to restore a state of equilibrium between the elements.
(b) the maximum power flow possible through some particular point in the system when the entire or part of the system is disturbed.
(c) both (a) and (b).
(d) neither (a) nor (b).

18. Steady-state stability of a power system is the ability of the power system to

(a) maintain voltage at the rated voltage level.
(b) maintain frequency exactly at 50 Hz.
(c) maintain a spinning reserve margin at all times.
(d) maintain synchronism between machines and on external tie lines.

19. Transient disturbances are caused by

(a) sudden load changes.
(b) switching operations.
(c) inadvertent tripping of lines and generators.
(d) faults in the power system.
(e) all of the above.

20. Transient stability of a 3-phase power systems having more than one synchronous generator is not affected by which one of the following specifications?

(a) Initial operating conditions of generators.
(b) Quantum of large power disturbance.
(c) Fast fault clearance and reclosure.
(d) Small changes in system frequency.