Description : Thermal overload relays are used to protect the motor against over current due to (a) short-circuits (b) heavy loads (c) grounds (d) all of the above
Last Answer : (b) heavy loads
Last Answer : The inverse definite mean time relays are used for over current and earth fault protection of transformer against internal short-circuits.
Description : Large internal faults are protected by (a) merz price percentage differential protection (b) mho and ohm relays (c) horn gaps and temperature relays (d) earth fault and positive sequence relays
Last Answer : (a) merz price percentage differential protection
Description : H.R.C. fuses provide best protection against (a) overload (b) reverse current (c) open-circuits (d) short-circuits
Last Answer : (d) short-circuits
Description : Protective relays are devices that detect abnormal conditions in electrical circuits by measuring (a) current during abnormal condition (b) voltage during abnormal condition (c) constantly the electrical quantities which differ during normal and abnormal conditions (d) none of the above
Last Answer : (c) constantly the electrical quantities which differ during normal and abnormal conditions
Description : Fault diverters are basically (a) fuses (b) relays (c) fast switches (d) circuit breakers
Last Answer : (c) fast switches
Description : The single phasing relays are used for the protection of (a) single phase motors only (b) two phase motors only (c) two single phase motors running in parallel (d) three phase motors
Last Answer : (d) three phase motors
Description : Discrimination between main and back up protection is provided by the use of relays which are (a) fact (b) sensitive (c) slow (d) none of the above
Last Answer : (c) slow
Description : Which of the following devices will receive voltage surge first travelling on the transmission line ? (a) Lightning arresters (b) Relays (c) Step-down transformer (d) Switchgear
Last Answer : (a) Lightning arresters
Description : A thermal protection switch can protect against (a) short-circuit (b) temperature (c) overload (d) over voltage
Last Answer : (c) overload
Description : Which of the following statements is incorrect ? (a) Lightning arrestors are used before the switchgear (b) Shunt reactors are used as compensation reactors (c) The peak short current is (1.8 xV2) ... component (d) The MVA at fault is equal to base MVA divided by per unit equivalent fault reactance
Last Answer : (a) Lightning arrestors are used before the switchgear
Description : The delay fuses are used for the protection of ________ . (a) motors (b) power outlet circuits (c) fluorescent lamps (d) light circuits
Last Answer : (a) motors
Description : Ungrounded neutral transmission system is not recommended because of system (a) insulation being overstressed due to over voltages (b) insulation overstress may lead to failure and subsequent phase to phase faults (c) being inadequately protected against ground fault (d) all of the above
Last Answer : (d) all of the above
Description : Directional relays are based on flow of (a) power (b) current (c) voltage wave (d) all of the above
Last Answer : (a) power
Description : Relays can be designed to respond to changes in (a) resistance, reactance or impedance (b) voltage and current (c) light intensity (d) temperature (e) all above
Last Answer : (e) all above
Description : relay is preferred for phase fault on short transmission line. (a) Induction type (b) Reactance (c) Impedance (d) None of the above
Last Answer : (b) Reactance
Description : To reduce short circuit fault currents are used. (a) reactors (b) resistors (c) capacitors (d) none of the above
Last Answer : (a) reactors
Description : Overfluxing protection is recommended for (a) distribution transformer (b) generator transformer of the power plant (c) auto-transformer of the power plant (d) station transformer of the power plant
Last Answer : (b) generator transformer of the power plant
Description : For which of the following ratings of the transformer differential protection is recommended ? (a) above 30 kVA. (b) equal to and above 5 MVA (c) equal to and above 25 MVA (d) none of the above
Last Answer : (b) equal to and above 5 MVA
Description : Distance relays are generally (a) split-phase relays (b) reactance relays (c) impedance relays (d) none of the above
Last Answer : (d) none of the above
Description : relays are used for phase faults on long line. (a) Impedance (b) Reactance (c) Either of the above (d) None of the above
Last Answer : (a) Impedance
Description : 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
Last Answer : (c) both (a) and (b)
Description : D.C. shunt relays are made of (a) few turns of thin wire (b) few turns of thick wire (c) many turns of thin wire (d) many turns of thick wire
Last Answer : (c) many turns of thin wire
Description : Overload relays are of...... type. (a) induction (b) solid state (c) thermal (d) electromagnetic (e) all above
Description : A transmission line is protected by (a) inrush protection (b) distance protection (c) time graded and current graded over current protection (d) both (b) and (c) (e) none of the above
Last Answer : (d) both (b) and (c)
Description : Which of the following statements is incorrect? (a) Station batteries are used to operate relay only (b) The lightning arresters are basically surge diverters (c) An impedance relay has maximum fault current when fault occurs near the relay (d) A high speed relay has an operation of 1 to 2 cycles
Last Answer : (a) Station batteries are used to operate relay only
Description : The relay with inverse time characteristic will operate within (a) 1.5 sec (b) 5 to 10 sec (c) 5 to 20 sec (d) 20 to 30 sec (e) none of the above
Last Answer : (b) 5 to 10 sec
Description : With which of the following, a circuit breaker must be equipped for remote operation ? (a) Inverse time trip (b) Time-delay trip (c) Shunt trip (d) None of the above (e) All of the above
Last Answer : (c) Shunt trip
Description : Circuit breakers are essentially (a) current carrying contacts called electrodes (b) arc extinguishers (c) circuits to break the system (d) transformers to isolate the two systems (e) any of the above
Last Answer : (a) current carrying contacts called electrodes
Description : 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 (e) none of the above
Last Answer : (c) interception, conduction and dissipation
Description : The short circuit in any winding of the transformer is the result of (a) mechanical vibration (b) insulation failure (c) loose connection (d) impulse voltage
Last Answer : (d) impulse voltage
Description : Over voltage protection is recommended for (a) hydro-electric generators (b) steam turbine generators (c) gas turbine generators (d) all of the above (e) none of the above
Description : Which of the following is the demerit of a 'constant voltage transmission system' ? (a) Increase of short-circuit current of the system (b) Availability of steady voltage at all loads at ... of carrying increased power for a given conductor size in case of long-distance heavy power transmission
Last Answer : (a) Increase of short-circuit current of the system
Description : Circuit breakers usually operate under (a) transient state of short-circuit current (b) sub-transient state of short-circuit current (c) steady state of short-circuit current (d) after D.C. component has ceased
Last Answer : (a) transient state of short-circuit current
Description : For which of the following protection from negative sequence currents is provided ? (a) Generators (b) Motors (c) Transmission line (d) Transformers
Last Answer : (a) Generators
Description : 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 (e) None of the above
Last Answer : (a) Rewireable fuse
Description : Air blast circuit breaker is used for (a) over currents (b) short duty (c) intermittant duty (d) repeated duty
Last Answer : (d) repeated duty
Description : 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
Last Answer : (b) higher frequencies entering generator or transformer units
Description : Purpose of Directional inverse Over current & earth fault relay; type- CDD
Last Answer : Directional phase or earth fault protection of ring-mains, parallel transformers, transformer feeders, parallel feeders etc., employing the time graded principle.; This relay comprises an inductive ... induction disc unit. The directional unit is normally provided with voltage polarising coils.
Description : Inverse definite minimum time lag relay is also called ___________ (A) pilot relay. (B) differential relay. (C) over current relay. (D) directional overcurrent relay.
Last Answer : Ans: B Inverse definite minimum time lag relay characteristic is inverse but minimum time is fixed. The operating time is inversely proportional to the magnitude of actuating quantity.
Description : transmission line has reflection coefficient as one. (a) Open circuit (b) Short-circuit (e) Long (d) None of the above
Last Answer : (a) Open circuit
Description : Which of the following parameter can be neglected for a short line ? (a) Inductance (b) Capacitance (c) Resistance (d) Reactance
Last Answer : (b) Capacitance
Description : Short-circuit currents are due to (a) single phase to ground faults (b) phase to phase faults (c) two phase to ground faults (d) three phase faults (e) any of these
Last Answer : (e) any of these
Description : A.C. network analyser is used to solve problems of (a) load flow (b) load flow and short-circuit (c) load flow and stability (d) load flow, short-circuit and stability (e) none of the above
Last Answer : (d) load flow, short-circuit and stability
Description : Shunt capacitance is neglected while considering (a) short transmission line (b) medium transmission line (c) long transmission line (d) medium and long transmission lines
Last Answer : (a) short transmission line
Description : Motor controllers are seldom troubled by grounds because ________________. A. cabinet heaters always keep internal components dry B. special insulation is used on wire for vital circuits C. ... on controller panels greatly reduce vibration D. contactors and relays are mounted on nonconducting panels
Last Answer : Answer: D
Description : Why asymmetrical breaking current is higher than the symmetrical breaking current in a circuit breaker?
Last Answer : Asymmetrical breaking current is the rms value of the combined sum of the dc and ac components of the short circuit current at the instant of separation of the breaker contacts while ... the ac component alone. Thus asymmetrical breaking current is higher than the symmetrical breaking current.
Description : What is meant by Current Chopping?
Last Answer : Current Chopping is a phenomenon of current interruption before the natural current zero is reached.
Description : Arc in a circuit breaker is interrupted at (a) zero current (b) maximum current (c) minimum voltage (d) maximum voltage
Last Answer : (a) zero current