Switchgear and Protection Mcq with Answers

21. The power transmission capacity of a transmission line is

(a) proportional to transmission voltage.
(b) proportional to the square of transmission voltage.
(c) inversely proportional to transmission voltage.
(d) inversely proportional to the square of transmission voltage.

22. The load carrying capability of a long ac transmission line is

(a) always limited by the conductor size.
(b) limited by stability considerations.
(c) reduced at low ambient temperatures.
(d) decreased by the use of bundled conductors of single conductors.

23. Maximum power will be transferred from the sending end to the receiving end by a transmission line when

(a) the line reactance is √3 times its resistance, i.e., X = √3R.
(b) the torque angle δ = 90°.
(c) both (a) and (b).
(d) neither (a) nor (b).

24. The steady state stability limits for round rotor and salient pole 3-phase synchronous generator are attained at the values of power angle δ

(a) = π/2, and = π/2, respectively.
(b) < π/2, and < π/2, respectively.
(c) < π/2, and = π/2, respectively.
(d) = π/2, and < π/2, respectively.

25. Which one of the following statements is true?

(a) steady-state stability limit is greater than transient stability limit.
(b) steady-state stability limit is equal to transient stability limit.
(c) steady-state stability limit is less than the transient stability limit.
(d) no generalization can be made regarding the equality or otherwise of the steady, state stability limit and transient stability limit.

26. Steady-state stability of a power system is improved by

(a) reducing fault clearing time.
(b) using double circuit line instead of single circuit line.
(c) single pole switching.
(d) decreasing generator inertia.

27. The methods employed in improving the system stability are

(a) increasing the system voltage only.
(b) reducing the transfer reactance only.
(c) using high-speed auto-reclosing circuit breaker only.
(d) using all (a), (b), (c) together.

28. Series capacitors are used to

(a) compensate for line inductive reactance and improve the stability of the power system.
(b) improve the voltage.
(c) reduce fault level.
(d) improve the power factor.

29. In a multimachine interconnected system, subsequent to a 3-phase fault, the transient stability is examined by

(a) equal-area criterion.
(b) solution of swing equation.
(c) either by equal-area criterion or by solution of swing equation
(d) combination of equal-area criterion and solution of swing equation.

30. The equal area criterion of stability is used for

(a) no load on the bus-bar.
(b) one machine and infinite bus-bar.
(c) more than one machine and infinite bus-bar.
(d) none of the above.

31. The ‘equal area criterion’ for the determination of transient stability of a synchronous machine connected to an infinite bus

(a) ignores line as well as synchronous machine resistances and shunt capacitances.
(b) assumes accelerating power acting on the rotor as constant.
(c) ignores the effect of voltage regulator and governor but considers the inherent damping present in the machine.
(d) takes into consideration the possibility of machine losing synchronism after it has survived during the first swing.

32. The ‘Equal area criterion’ for the determination of transient stability of the synchronous machine connected to an infinite bus:

(a) Ignores line as well as synchronous machine resistances and shunt capacitances.
(b) Assumes accelerating power acting on the rotor as constant.
(c) Ignores the effect of voltage regulator and governor but considers the inherent damping present in the machine.
(d) Takes into consideration the possibility of machine loosing synchronism after it has survived during the first swing.

33. For what value of damping parameter, the transient stability is assured by equal area criterion?

(a) Independent of systems damping.
(b) If only damping is exactly zero.
(c) For all values of damping parameters.
(d) If only damping is positive and finite.

34. Equal area criterion gives the information regarding

(a) stability region.
(b) absolute stability.
(c) relative stability.
(d) swing curves.

35. The critical clearing time of a fault in power system is related to

(a) reactive power limit.
(b) short-circuit limit.
(c) steady-state stability limit.
(d) transient stability limit.

36. With fault clearing time, the transient stability limit of a power system

(a) increases.
(b) decreases.
(c) first increases and then decreases.
(d) first decreases and then increases.

37. For which one of the following types of motors, is the equal-area criterion for stability applicable ?

(a) Three phase synchronous motor.
(b) Three-phase induction motor.
(c) DC series motor.
(d) DC compound motor.

38. The inertia constants of two groups of machines which do not swing together are M₁ and M₂ such that M₁ > M₂. It is proposed to add some inertia to one of the two groups of machines for improving the transient stability of the system. It should be added to

(a) M₁
(b) M₂
(c) either to M₁ or to M₂.
(d) neither of the above.

39. The transient stability limit of a power system can be appreciably increased by introducing

(a) series inductance.
(c) series capacitance.
(b) shunt inductance.
(d) shunt capacitance.

40. Consider the following statements: The transient stability of the power system under unbalanced fault condition can be effectively improved by

1. excitation control.
2. phase shifting transformer.
3. single-pole switching of circuit breakers.
4. increasing the turbine input.

Of these statements
(a) 1 and 2 are correct.
(b) 2 and 3 are correct.
(c) 3 and 4 are correct.
(d) 1 and 3 are correct.