## electrical

### Switchgear and Protection MCQ Objective Questions and Answers Page - 5

1.
 Where severe synchronising swing occur, the relay employed is A Impedance relay B Mho relay C Reactance relay D Induction relay Answer : B Explanation :
2.
 Which of the following relays has inherent directional characteristic  ? A Mho B Reactance C Impedance D None of the above Answer : A Explanation :
3.
 A differential relay responds to A Algebraic difference of two or more similar electrical quantities. B Phasor difference of two or more similar electrical quantities. C Algebraic difference between two currents. D Algebraic difference between two voltages. Answer : B Explanation :
4.
 Difference relays are used for protection of equipment against A Internal faults B Overcurrent C Reverse current D Reverse power Answer : A Explanation :
5.
 Undervoltage relays are mainly used for A Motor protection B Transformer protection C Transformer protection D All of these Answer : D Explanation :
6.
 In a biased differential relay the bias is defined as a ratio of A Number of turns of restraining and operating coil. B Operating coil current and restraining coil current. C Fault current and Operating coil current. D Fault current and Restraining coil current. Answer : A Explanation :
7.
 Differential relays are used for protection of A Feeders B Alternators C Transformers D All of these Answer : D Explanation :
8.
 Both voltage and current signals are required for A A plain overcurrent relay B A differential relay C A direction relay D A biased differential relay Answer : C Explanation :
9.
 The relay used for feeder protection is A Undervoltage relay B Translay relay C Thermal relay D Buchholz relay Answer : B Explanation :
10.
 In the case of transmission line protection, overcurrent relay is used A Only up to  110 kV. B Only up to  220 kV. C Only up to  50 kV. D Only up to  1,100 kV. Answer : C Explanation :
11.
 Phase relays are used to provide protection against A Single line to ground fault. B Three phase fault only. C Phase faults involving two or more phases. D Double phase to ground fault only. Answer : C Explanation :
12.
 In a 3-phase circuit, residual current means the flow of  __________ current. A Negative-sequence B Zero sequence C Dc transient D Answer : B Explanation :
13.
 Zero- sequence current is used for relaying purposes only in the case of A Phase overcurrent relay. B Phase impedance relay. C Ground overcurrent relay. D Ground impedance relay. Answer : C Explanation :
14.
 Over conventional electromechanical relays, the transistor relays have the advantages of A Low power consumption, less maintenance and greater sensitivity. B Quick operation and high reset to pick-up ratio. C Wide range of characteristics approaching more or less to ideal requirements. D All of the above. Answer : D Explanation :
15.
 Over conventional electromechanical relays, the transistor relays have the limitations of A Characteristics varying temperature and ageing. B Low short-time overload capacity. C Reliability dependent upon the large number of small components and their electrical connections. D All of the above. Answer : D Explanation :
16.
 In a static overcurrent relay, inverse time characteristics are obtained by A A transistor amplifier. B An integrating circuit. C A transistor switch. D A differentiating circuit. Answer : B Explanation :
17.
 Two-input phase comparator in a static relay is made up of a A Transformer amplifier. B Transistor logic circuit. C Rectifier bridge. D Thyristor bridge. Answer : C Explanation :
18.
 The phase comparators in case of static relays and electromechanical relay normally are A Cosine and sine comparators respectively. B Sine and cosine comparators respectively. C Both are sine comparators. D Both are cosine comparators. Answer : A Explanation :
19.
 Merz-Price protection is employed for protection of A Alternators B Transformers C Transmission lines. D Both (a) and (b) Answer : D Explanation :
20.
 Negative-sequence voltages in the stator induces. A High frequency currents in the rotor. B High frequency voltage in the rotor. C Low frequency currents in the rotor. D High frequency currents in the stator. Answer : A Explanation :
21.
 The short-circuit current of an alternator, in case of line to line fault, depends on its A Short-circuit resistance. B Transient reactance. C Synchronous reactance. D None of the above. Answer : C Explanation :
22.
 We do not require any protection against prime mover failure in case of A Turbo-generator sets. B Hydrogenator sets. C Diesel-engine driven alternators. D Back pressure turbo-generators. Answer : A Explanation :
23.
 For the protection of stator winding of an alternator against internal fault involving ground, the relay used is a A Biased differential relay. B Directional overcurrent relay. C Plain impedance relay. D Buchholz relay. Answer : A Explanation :
24.
 The bias factor S in unit protection synchronous generators A Lies between  0.05  and  0.1 pu. B Is less than  0.05 pu C Lies between  0.1 to 0.25 pu. D Is greater than  0.025 pu. Answer : A Explanation :
25.
 Field failure in an alternator occurs due to A Failure of exciter B Faulty field circuit breaker. C Inrush of large currents D Both (a) and (b) Answer : D Explanation :
26.
 A soon as a fault develops in a generator stator, it is essential to suppress field excitation, otherwise A Terminal voltage will drop. B It may lead to loss of synchronism. C It will continue to supply power to the stator winding fault. D All of the above. Answer : C Explanation :
27.
 If there is an open circuit in the field circuit of a generator A The generator will continue to operate as an induction generator supplying load at a very low leading power factor. B The supply voltage will drop, and the system stability will be affected. C The circulating current at slip frequency may overhead the generator. D All of the above. Answer : D Explanation :
28.
 The earth fault in stator causes A Arcing to core. B Severe heating in conductors and thereby damaging the insulation. C Open-circuit in the stator D Both (a) and (b) Answer : D Explanation :
29.
 Failure of insulation on stator winding of generator results in A Short circuit between turns. B Short circuit between one or more phases and earth. C Short circuit between phases. D All of the above. Answer : D Explanation :
30.
 The magnitude of earth-fault current for a given fault position within a winding depends upon A The winding connections. B The method of neutral grounding. C Unmatched characteristics of CTs. D Both (a) and (b) Answer : D Explanation :
31.
 For the protection of a large squirrel-cage induction motor against single phase normally A An overcurrent relay is used. B A differential relay is used. C A directional relay is used. D Negative sequence current sensitive relay is used. Answer : D Explanation :
32.
 The main function of undervoltage protective device generally employed with a motor starter is to A Open the supply circuit on failure of power supply. B Control the motor voltage. C Prevent the opening of supply circuit. D None of the above. Answer : A Explanation :
33.
 While adding extra stop buttons to an existing control system they must be in A Parallel to the load. B Series with the contactor coil. C Series with the motor. D Parallel to the start button. Answer : B Explanation :
34.
 The types of faults that occur in electric motors are A Stator B Overload C Undervoltage D All of the above Answer : D Explanation :
35.
 Negative-sequence currents flow in the stator windings of an ac motor due to A Unbalanced in the supply voltage B Unbalanced load C Phase reversal D Wither (a) or (b) Answer : D Explanation :
36.
 A negative sequence relay is commonly used to product A An alternator B A transformer C A transmission line D A bus bar Answer : A Explanation :
37.
 Earth fault protection for an electric motor is provided by means of A Instantaneous overcurrent relay. B Instantaneous relay having a setting of approximately  30%  of motor rated current in the residual circuits of two  CTs. C Ground wire D Both (b) and (c) Answer : D Explanation :
38.
 Any winding of a power transformer develops short-circuit owing to A Loose connection B Insulation failure C Impulse voltage D Mechanical vibrations Answer : B Explanation :
39.
 Which of the following relays has the capacity of anticipating the possible major fault in a transformer ? A Overcurrent relay B Differential relay C Buchholz relay D Over-fluxing relay Answer : C Explanation :
40.
 Which relay is used to detect and protect internal faults of a transformer  ? A Buchholz B Directional relay C Thermal relay D Distance relay Answer : A Explanation :
41.
 The delay fuses arc used for the protection of A Motors B Power outlet circuits C Fluorescent lamps D Light circuits Answer : A Explanation :
42.
 Which of the following is the least expensive protection for overcurrent is low voltage system? A Rewireable fuse B Isolator C Oil circuit breaker D Air break circuit breaker Answer : A Explanation :
43.
 Resistance grounding is used for voltage between A 33 kV to 66 kV B 11 kV to 33 kV C 3.3 kV to 11 kV D None of the above Answer : C Explanation :
44.
 The contacts of high voltage switches used in power system are submerged in oil. The main purpose of the oil is to A Lubricate the contacts B Insulate the contacts from switch body C Extinguish the arc D All of the above Answer : C Explanation :
45.
 In Railway applications   ______________   circuit breaker is used. A SF6 B Bulk oil C Minimum oil D Air break Answer : D Explanation :
46.
 To protect most of the electrical equipment handling low power, the types of relays used are A Thermocouple B Electronic and bimetallic C Both (a) and (b) D None of the above Answer : C Explanation :
47.
 Wave trap is used to trap waves of A Power frequencies B Higher frequencies entering generator or transformer units C Either of the above D None of the above Answer : D Explanation :
48.
 The reflection co-efficient at the open circuited end of a transmission line is A Zero B Infinity C Unity D None of the above Answer : C Explanation :
49.
 For the protection of power station buildings against direct strokes the requirements are A Interception B Interception and conduction C Interception, conduction and dissipation D Interception, conduction, dissipation and reflection Answer : C Explanation :