Circuit Breakers Part 2 Online MCQ EE

Circuit Breakers Part 2

Instructions: Click the answer button to see the correct answer.

Ques. The arc voltage produced in ac circuit breaker is

1. In phase opposition to the arc current.
2. lagging the arc current by 90°
3. leading the arc current by 90°
4. In phase with the arc current

Answerd

Ques. As the force on contact is increased, the contact resistance will

1. increase exponentially
2. remain unaltered
3. increase linearly
4. decrease.

Answer d

Circuit Breakers Part 2

Ques. The heat produced at the contact point, due to passage of current, will least depend on

1. temperature of the surrounding medium.
2. current flowing
3. contact resistance
4. time during which the current flows

Answer a

Ques. For the contact and their material, which of the following should have low value

1. Thermal conductivity
2. Thermal capacity
3. Contact resistance
4. All of the above.

Answer c

Ques. Minimum arcing voltage will be least in case of

1. tungsten
2. carbon
3. silver.
4. graphite

Answer c

Circuit Breakers Part 2

Ques. Minimum arcing voltage for platinum is 16 V. It can be therefore concluded that when the voltage is below 16 V

1. it will not be possible to interrupt the circuit
2. it will be possible to interrupt any value of current without bringing contact closer to one another.
3. it will be possible to interrupt any value of current without arcing
4. it will not be possible to pass the current

Answer c

Ques. Oil immersion of contacts is the method of

1. arc prevention
2. none of the above.
3. de ionization
4. arc dispersion

Answer d

Ques. Which of the following is not the method of arc dispersion ?

1. Oil immersion of contacts
2. De ionization of arc path.
3. Use of rectifiers
4. Magnetic blow out of arc

Answer c

Ques. Which of the following contact point metals has the highest melting point ?

1. Gold
2. Silver
3. Copper.
4. Tungsten

Answer d

Ques. The arc voltage produced in the circuit breaker is always

1. in phase with arc current
2. all of these
3. leading the arc current by 90°
4. lagging the arc current by 90°

Answer a

Circuit Breakers Part 2

Ques. Ionization process during arc is generally accompanied by emission of

1. light
2. all of these
3. heat
4. sound

Answer b

Ques. Sparking between contacts can be reduced by

1. inserting resistance in the line
2. all of these
3. inserting a capacitor in series with the contacts
4. inserting a capacitor in parallel with the contacts.

Answer d

Ques. For magnetic blow out of arc the magnetic field is produced

1. all of these
2. parallel to the axis of the arc
3. in the load circuit
4. at right angles to the axis of the arc.

Answer d

Ques. Cool gases are solids brought into the arc stream assist in quenching the arc mainly by

1. providing arc shield
2. De ionization
3. reducing current density
4. providing parallel paths.

Answer b

Ques. Sparking occurs when a load is switched off because the circuit has

1. high capacitance
2. all of these
3. high inductance
4. high resistance.

Answer c

Circuit Breakers Part 2

Ques. HRC fuses are

1. High resistance and Capacitance fuses
2. Heat reflecting cool fuses
3. High rupturing capacity fuses.
4. Holding and Resisting current fuses

Answer c

Ques. Which of the following metals does not amalgamate with mercury ?

1. Tungsten
2. Molybdenum
3. All of these
4. Nickel alloy

Answer c

Ques. For the same current, which of the following fuse wires will have the least fusing time ?

1. 20 SWG TIN – 10 A
2. 18 SWG TIN – 12.5 A
3. 24 SWG TIN-5 A.
4. 22 SWG TIN-7.5 A

Answer c

Ques. An automatic device that operates at present values is known as

1. mercury switch
2. relay
3. contractor.
4. fuse

Answer b

Circuit Breakers Part 2

Ques. The basic function of a circuit breaker is to

1. ionize the surrounding air
2. produce the arc
3. extinguish the arc.
4. transmit voltage by arcing

Answer c

Ques. In a circuit breaker the arc is indicated by the process of I. Thermal emission II. Ionization of oil III. High temperature of air IV. Field emission

1. I and II only
2. I and IV only.
3. I, II and III only
4. II, III and IV only

Answer b

Ques. The power factor of the arc in circuit breaker is

1. always leading.
2. always unity
3. always zero
4. always lagging

Answer b

Ques. Air blast circuit breakers are usually used for

1. permanent break
2. repeated duty.
3. intermittent duty
4. instantaneous duty

Answer b

Circuit Breakers Part 2

Ques. Flame proof switch gears are usually preferred

1. substations
2. in mines
3. on transmission lines of low voltage
4. in high MVA capacity circuits.

Answer b

Ques. Pressure of air in air blast circuit breakers is usually

1. 1 – 5 kg/cm sqr
2. 35-100 kg/cm sqr
3. 10-30 kg/cm sqr
4. 5 – 10 kg/cm sqr

Answer c

Ques. Air used in air blast circuit breaker

1. must have oil mist
2. must be free from moisture.
3. must have least carbon dioxide
4. must be ionized

Answer b

Ques. In a circuit breaker the time duration from the instant of fault to the instant of energizing of the trip coil is known as

1. lag time
2. operation time.
3. lead time
4. protection time

Answer d

Circuit Breakers Part 2

Ques. In a circuit breaker the lime duration from the instant of the fault to the extinction of arc is known as

1. lead time.
2. total clearing time
3. operation time
4. lag time

Answer b

Ques. In a circuit breaker the lime duration from the instant of fault to the instant of closing of contact is known as

1. Recycle time
2. Re closing time.
3. Total time
4. Gross time

Answer b

Ques. For high speed circuit breakers the total lime is nearly

1. Ten cycles.
2. Few cycles
3. One cycle
4. Half cycle

Answer d

Ques. For a high speed circuit breaker the total clearing time is nearly

1. 10 to 15 cycles
2. less than 50 cycles.
3. 1 to 2 cycles
4. 5 to 10 cycles

Answer c

Ques. If the power factor is zero, the active recovery voltage will be

1. minimum
2. 0.707
3. maximum.
4. 0.5

Answer c

Circuit Breakers Part 2

Ques. Which of the following is not a part of the circuit breaker ?

1. Explosion pot
2. Conservator
3. Fixed and moving contacts
4. Operating mechanism.

Answer b

Ques. A circuit breaker will normally operate

1. Whenever fault in the line occurs.
2. When the power is to be supplied
3. When the line is to be checked
4. When the switch is put on

Answer a

Ques. Which of the following circuit breaker will produce the least arc energy ?

1. All will produce same energy.
2. Air blast circuit breaker
3. Minimum oil circuit breaker
4. Plain oil circuit breaker

Answer b

Circuit Breakers Part 2

Ques. For a circuit breaker ‘break time’ is

1. all of these
2. opening time + arc duration
3. opening time + arc duration + resistor current duration.
4. same as opening time

Answer c

Ques. The breaking capacity of a circuit breaker in MVA (3 phase) is given by

1. rated service voltage x rated symmetrical current
2. √2x rated service voltage x rated symmetrical current.
3. 1.1 x rated service voltage x rated symmetrical current
4. √3x rated service voltage x rated symmetrical current.

Answer d

Ques. Which relay is used for feeders ?

1. Buchholz relay.
2. Merz price protection
3. MHO relay
4. Translay relay

Answer d

Ques. Which of the following relays is used on transformers ?

1. Merz price relay
2. Buchholz relay
3. MHO relay
4. None of these

Answer b

Ques. MHO relay is used for

1. circuit breakers
2. transmission lines
3. feeders.
4. rectifiers

Answer b

Ques. Merz-price protection is used on

1. capacitor bank
2. substations
3. generators.
4. induction motor

Answer c

Circuit Breakers Part 2

Ques. The values of fault current depend on

1. voltage at the faulty point and total impedance up to the fault
2. none of these
3. total impedance up to the fault
4. voltage at the faulty point

Answer a

Ques. The advantage of neutral earthing is

1. all of these
2. freedom from persistent arcing grounds
3. simplified design of earth fault protection
4. over-voltages due to lightning can be discharged to the earth

Answer a

Ques. The over-voltage surges in power systems may be caused by

1. resonance
2. lightning
3. any of these
4. switching

Answer c

Ques. The protection against over-voltage due to lightening is provided by

1. low tower footing resistance
2. use of overhead ground wires
3. any of these
4. use of surge diverters

Answer c

Circuit Breakers Part 2