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
Description : A thermal protection switch can protect against (a) short-circuit (b) temperature (c) overload (d) over voltage
Last Answer : (c) overload
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 : The inverse definite mean time relays are used for over current and earth fault protection of transformer against (a) heavy loads (b) internal short-circuits (c) external short-circuits (d) all of the above
Last Answer : (b) internal short-circuits
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 : 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 : 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 : 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 : 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 : 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 : 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 : Directional relays are based on flow of (a) power (b) current (c) voltage wave (d) all of the above
Last Answer : (a) power
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 : Fault diverters are basically (a) fuses (b) relays (c) fast switches (d) circuit breakers
Last Answer : (c) fast switches
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 : 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 : Induction cup relay is operated due to changes in (a) current (b) voltage (c) impedance (d) all of the above
Last Answer : (d) all of the above
Description : If overloading a DC machine becomes necessary in an emergency, you should ____________. A. cool the machine with portable blowers and fans B. hold thermal overload relays open with blocks of ... the windings for cooling D. increase the residual magnetism value of windings to reduce eddy currents
Last Answer : Answer: A
Last Answer : Thermal overload relays are used to protect the motor against overcurrent due to heavy loads.
Description : Thermal circuit breaker has (a) delayed trip action (b) instantaneous trip action (c) both of the above (d) none of the above
Last Answer : (a) delayed trip action
Description : A three-phase, induction-type motor experiences an open in one phase. Which of the listed automatic protective devices will prevent the machine from being damaged? A. Overspeed trip B. Thermal overload relay C. Three-pole safety switch D. Magnetic blowout coil
Last Answer : Answer: B
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 : 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 : 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 : 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 : The under voltage relay can be used for (a) generators (b) busbars (c) transformers (d) motors (e) all of the above
Last Answer : (e) all of the above
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 : When a wave propagates on a transmission line, it suffers reflection several times at (a) tapping (b) load end (c) sending end (d) sending and other end (e) all of the above
Last Answer : (d) sending and other end
Description : The line insulation is the insulation level of the station equipment. (a) less than (b) same as (c) more than (d) proportional to (e) not directly related with
Last Answer : (e) not directly related with
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 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 (e) none of the above
Last Answer : (c) extinguish the arc
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 : The time of closing the cycle, in modern circuit breakers is (a) 0.003 sec (b) 0.001 sec (c) 0.01 sec (d) 0.10 sec (e) none of the above
Last Answer : (a) 0.003 sec
Description : The voltage appearing across the contacts after opening of the circuit breaker is called______voltage. (a) recovery (b) surge (c) operating (d) arc (e) none of the above
Last Answer : (a) recovery
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 : The current zero interruption, in oil and air blast circuit breakers, is achieved by (a) lengthening of the gap (b) cooling and blast effect (c) both (a) and (b) (d) deionizing the oil with forced air (e) none of the above
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 : 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 : SF6 gas (a) is yellow in colour (b) is lighter than air (c) is nontoxic (d) has pungent small (e) none of the above
Last Answer : (c) is nontoxic
Description : The main function of a fuse is to (a) protect the line (b) open the circuit (c) protect the appliance (d) prevent excessive currents (e) none of the above
Last Answer : (d) prevent excessive currents
Description : When power is restored after a complete power failure, a steering gear pump motor will ____________. A. have to be restarted B. have to be reset C. restart automatically D. trip its overload relays
Last Answer : Answer: C
Description : What is the normal setting of overload relays?
Last Answer : Ask E/O. Normally 90-100% of rated normal current. Sometimes can be set to 105% of rated current.
Last Answer : Overload relays are of induction, solid state, thermal, electromagnetic type.
Description : For an Resistive Load and Inductive load considered for switching operation of circuit breaker, Switching of which load is difficult and Why?
Last Answer : In case of switching resistive load, current and voltage will be in phase i.e,when during current zero voltage also will be zero in case of resistive load. Hence the voltage at the ... maximum. This results in re-striking of arc once again. Therefore switching inductive load will be difficult
Description : What is re-striking voltage?
Last Answer : The Re-striking voltage may be defined as the resultant transient voltage which appears across the breaker contacts at the instant of arc extinction
Description : When does an arc extincts?
Last Answer : If the rate of rise of re-striking voltage (RRRV) is less than rate of rise of dielectric strength between the breaker contacts arc will not sustain and extincts
Description : What is recovery voltage in circuit breaker?
Last Answer : Recovery voltage in circuit breakers is defined as the power frequency rms voltage which appears across the breaker contacts after the transient oscillations die out and the final extinction of the arc ... poles of the circuit breaker. It is the voltage developed after the arc extinction is competed
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.