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
Last Answer : Interruption of large currents by relay requires arc suppressing blow out coils, wide separation of the opened contacts, high speed opening of contacts.
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 : 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 : 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 : 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 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 : 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 : 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 : 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 operating speed depends upon (a) the spring tension (b) the rate of flux built up (c) armature core air gap (d) all of the above
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 : To reduce short circuit fault currents are used. (a) reactors (b) resistors (c) capacitors (d) none of the above
Last Answer : (a) reactors
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 : 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 : 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 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 : 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 : 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 : 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 : 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 : Admittance relay is _______ relay. (a) impedance (b) directional (c) non-directional (d) none of the above
Last Answer : (b) directional
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 : 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
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 : As shown in the illustration, all 'MS' contacts are opened and closed by means of ________. EL-0073 A. operating coils B. magnets C. manual operation of the master switches D. solenoid switches
Last Answer : Answer: C
Description : The arc resulting from the tripping of a circuit breaker is prevented from damaging the contacts by _____________. A. designing the contacts to open slowly B. directing the arc into an ... an inverse timed thermal trip for short circuit currents D. instantaneous magnetic trip for overload currents
Last Answer : Answer: B
Description : When the series field relay "FR" of the winch circuit shown in the illustration is energized during dynamic braking the _______________. EL-0102 A. shunt Field Relay "FR-B.O." is de-energized and contacts ... . shunt Field Relay "FR-B.O." opposes the series coil's flux and sets the mechanical brake
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 : Burning of controller contacts, when opening, is prevented by _____________. A. coating the contact surfaces lightly with petroleum jelly B. magnetic blowout coils C. an overvoltage release D. an overcurrent release
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 : An ideal nozzle design aims at (A) Minimising wall friction (B) Suppressing boundary layer separation (C) Both (A) & (B) (D) Neither (A) nor (B)
Last Answer : (C) Both (A) & (B)
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 : 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 : Series reactors should have (a) low resistance (b) high resistance (c) low impedance (d) high impedance
Last Answer : (a) low resistance
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 : 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 : Give the two methods of arc interruption?
Last Answer : High resistance interruption:-the arc resistance is increased by elongating, and splitting the arc so that the arc is fully extinguished Current zero method:-The arc is interrupted at current zero position that occurs100 times a second in case of 50Hz power system frequency in ac.
Description : In general AC distribution systems, arc interruption in vacuum circuit breakers are designed to function in a time period of (a) One cycle (b) Two to three cycles (c) Within ten cycles (d) None of the above
Last Answer : In general AC distribution systems, arc interruption in vacuum circuit breakers are designed to function in a time period of One cycle
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 : 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 : 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