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

1 Answer

Answer :

(d) prevent excessive currents

Related questions

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 : 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 : To reduce short circuit fault currents are used. (a) reactors (b) resistors (c) capacitors (d) none of the above

Last Answer : (a) reactors

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 : 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 : 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 : A thermal protection switch can protect against (a) short-circuit (b) temperature (c) overload (d) over voltage

Last Answer : (c) overload

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

Last Answer : (d) all of the above

Description : A differential relay measures the vector difference between (a) two currents (b) two voltages (c) two or more similar electrical quantities (d) none of the above

Last Answer : (c) two or more similar electrical quantities

Description : The material used for fuse must have (a) low melting point and high specific resistance (b) low melting point and -low specific resistance (c) high melting point and low specific resistance (d) low melting point and any specific resistance

Last Answer : (a) low melting point and high specific resistance

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 : 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 : 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 : The reflection co-efficient at the open circuited end of a transmission line. (a) zero (b) infinity (c) unity (d) none of the above

Last Answer : (c) unity

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 : 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 : 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

Last Answer : (c) both (a) and (b)

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 : 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 : 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 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 : 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 : 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 : 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 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 : 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 : 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 : The arc voltage produced in A.C. circuit breaker is always (a) in phase with the arc current (b) lagging the arc current by 90" (c) leading the arc current by 90° (d) none of the above

Last Answer : (a) in phase with the arc current

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 : In a circuit breaker the basic problem is to (a) maintain the arc (b) extinguish the arc (c) transmit large power (d) emit the ionizing electrons

Last Answer : (c) transmit large power

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

Last Answer : (d) all of the above

Description : Burden of a protective relay is the power (a) required to operate the circuit breaker (b) absorbed by the circuit of relay (c) developed by the relay circuit (d) none of the above

Last Answer : (b) absorbed by the circuit of relay

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 : Magnetic circuit breaker has ______ trip action. (a) delayed (b) instantaneous (c) both of the above (d) none of the above

Last Answer : (b) instantaneous

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 : 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 : Fault diverters are basically (a) fuses (b) relays (c) fast switches (d) circuit breakers

Last Answer : (c) fast switches

Description : Which of the following medium is employed for extinction of arc in air circuit breaker ? (a) Water (b) Oil (c) Air (d) SF6

Last Answer : (c) Air

Description : The arcing contacts in a circuit breaker are made of (a) copper tungsten alloy (b) porcelain (c) electrolytic copper (d) aluminium alloy

Last Answer : (a) copper tungsten alloy

Description : On which of the following routine tests are conducted ? (a) Oil circuit breakers (b) Air blast circuit breakers (c) Minimum oil circuit breakers (d) All of the above

Last Answer : (d) All of the above

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 : 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 : 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 : Bus coupler is very essential in arrangement (a) single bus (b) double bus, double breaker (c) main and transfer bus (d) all of the above

Last Answer : (c) main and transfer bus

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