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 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 : Series reactors should have (a) low resistance (b) high resistance (c) low impedance (d) high impedance
Last Answer : (a) low resistance
Description : Safety fuse wire used in domestic electrical appliances is made of metal of low (1) Resistance (2) Melting point (3) Specific gravity (4) Conductance
Last Answer : (2) Melting point Explanation: The fuse wire is based on the Joules law of heating which says that when the electric current is allowed to pass through a conductor, the conductor heats up and is ... . For this purpose the material used as fuse wire should have high resistance and low melting point.
Last Answer : Melting point
Description : In order that current should flow without causing excessive heating or voltage drop, the relay contacts should (a) have low contact resistance (b) be clean and smooth (c) be of sufficient size and proper shape (d) have all above properties
Last Answer : (d) have all above properties
Description : Insulation resistance of high voltage circuit breakers is more than (a) 1 mega ohms (b) 10 mega ohms (c) 100 mega ohms (d) 500 mega ohms
Last Answer : (c) 100 mega ohms
Description : A Fuse wire is characterized by – (1) High resistance and low melting point (2) High resistance and high melting point (3) Low resistance and high melting point (4) Low resistance and low melting point
Last Answer : (4) Low resistance and low melting point Explanation: A fuse is a type of low resistance resistor that acts as a sacrificial device to provide over current protection, of either the load or source ... melt if a current more than the safe current for the appliance starts flowing through the circuit.
Description : The nature of .fuse wire is – (1) high resistance and low melting point. (2) high resistance and high melting point. (3) low resistance and high melting point. (4) low resistance and low melting point.
Last Answer : (1) high resistance and low melting point. Explanation: A fuse or fusable link works by opening an electrical circuit when the current becomes too high. As the current increases, the temperature ... be connected in series with the appliance. Besides, it should have a comparatively high resistance.
Description : A Fuse wire is characterised by (1) High resistance and low melting point (2) High resistance and high melting point (3) Low resistance and high melting point (4) Low resistance and low melting point
Last Answer : Low resistance and low melting point
Description : The nature of fuse wire is (1) high resistance and low melting point. (2) high resistance and high melting point. (3) low resistance and high melting point. (4) low resistance and low melting point.
Last Answer : high resistance and low melting point.
Description : The material used for a fuse wire should have (a) high resistivity (b) high ductility (c) high melting point (d) low melting point
Last Answer : Ans:(d)
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 : A _______ is used to measure the stator % winding temperature of the generator. (a) thermocouple (b) pyrometer (c) resistance thermometer (d) thermometer
Last Answer : (c) resistance thermometer
Description : Resistance grounding is used for voltage between (a) 33kVto66kV (b) HkVto33kV (c) 3.3kVandllkV (d) none of the above
Last Answer : (c) 3.3kVandllkV
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 : Arc in a circuit behaves as (a) a capackive reactance (b) an inductive reactance (c) a resistance increasing with voltage rise across the arc (d) a resistance decreasing with voltage rise across the arc
Last Answer : (d) a resistance decreasing with voltage rise across the arc
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 : 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 : Overheating of relay contacts or contact born out is due to (a) slow making and breaking of load circuit contacts (b) foreign matter on the contact surface (c) too low contact pressure (d) all of the above
Last Answer : (d) all of the above
Description : Which of the following circuit breakers has high reliability and minimum maintenance ? (a) Air blast circuit breakers (b) Circuit breaker with SF6 gas (c) Vacuum circuit breakers (d) Oil circuit breakers
Last Answer : (b) Circuit breaker with SF6 gas
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 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 : Interruption of large currents by relay requires (a) arc suppressing blow out coils (b) wide separation of the opened contacts (c) high speed opening of contacts (d) all of the above
Description : Ionization in circuit breaker is facilitated by (a) high temperature (b) increase of mean free path (c) increasing field strength (d) all of the above
Description : An efficient and a well designed protective relaying should have (a) good selectivity and reliability (b) economy and simplicity (c) high speed and selectivity (d) all of the above
Description : The melting point of fuse wire should be high or low?
Last Answer : low
Description : Since fuse elements are made of zinc or any alloy of tin and lead, the melting point of the fuse element must be _____________. A. higher than that of copper B. lower than that of copper C. equal to that of copper D. reached when the conductor it is protecting becomes 'white hot.'
Last Answer : Answer: B
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.
Description : Why Isolation switches are provided along with the circuit breakers?
Last Answer : Isolation switches are provided for separating the disconnected element from the live portion of the system for the purpose of safety
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 : Air Blast Circuit Breakers Advantages Disadvantages
Last Answer : Air Blast Circuit Breakers Advantages Disadvantages In air blast circuit breakers, compressed air at a pressure of 20-30 kg/cm2 is employed as an arc quenching medium. Air blast circuit breakers ... air blast circuit breaker current chopping problem exists There is a problem of re-striking voltage
Description : Admittance relay is _______ relay. (a) impedance (b) directional (c) non-directional (d) none of the above
Last Answer : (b) directional
Description : Series capacitors are used to (a) compensate for line inductive reactance (b) compensate for line capacitive reactance (c) improve line voltage (d) none of the above
Last Answer : (a) compensate for line inductive reactance
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 : Air blast circuit breakers for 400 kV power system are designed to operate in (a) 100 microsecond (b) 50 millisecond (c) 0.5 sec (d) 0.1 sec
Last Answer : (b) 50 millisecond
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 : 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 : What will be the reflection coefficient of the wave of load connected to transmission line if surge impedance of the line is equal to load ? (a) Zero (b) Unity (c) Infinity (d) None of the above
Last Answer : (a) Zero
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 : 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
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 : 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 : 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