Online MCQ EE-Circuit Breakers Part Three

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

  1. Which of the following is a conducting medium for electric current ?
    1. Dissociated gas
    2. Low temperature gas
    3. High temperature gas
    4. Plasma.

    Answerd

  2. In circuit-breakers the contact space is ionized by
    1. thermal emission from surface of contacts
    2. any of these
    3. thermal ionization of gas
    4. field emission from the surface of contacts

    Answerb

  3. Which of the following are air-break switching devices ?
    1. Earthing switch
    2. Isolator
    3. All of these
    4. Limit switch

    Answerc

  4. Which of the following statement about SF6 gas is incorrect ?
    1. It has density 5 times that of air at 20 C
    2. It is non-inflammable
    3. It has dark yellow color.
    4. It is non-toxic gas

    Answerc

  5. SF6 gas is transported in
    1. liquid form in cylinders
    2. gas cylinders
    3. solid form in boxes
    4. air cylinders.

    Answera

  6. During arc extinction SF6 gas
    1. decomposes into SF4 and SF2
    2. decomposes into S and F ions
    3. gets oxidized
    4. reduces to SF3.

    Answera

  7. Dielectric strength of SF6 is
    1. less than that of air at atmospheric pressure
    2. less than that of oil used in OCB
    3. more than that of oil used in OCB
    4. more at lower pressure and low at higher pressures.

    Answerb

  8. Which of the following is the demerit of SF6 circuit breakers ?
    1. All of these
    2. Deterioration of quality of circuit breaker affects reliability of circuit breaker
    3. In flux of moisture in the gas system is dangerous
    4. sealing problem of gas

    Answera

  9. Sphere gaps are used for
    1. all of these
    2. measurement of impulse voltages
    3. measurement of high dc voltages
    4. measurement of high ac voltages

    Answera

  10. Flash point of dielectric is usually above
    1. 240°C.
    2. 100°C
    3. 80°C
    4. 140°C

    Answerd

  11. A fuse is normally a
    1. power factor correcting device.
    2. power limiting device
    3. current limiting device
    4. voltage limiting device

    Answerc

  12. Most of the fuses operate due to
    1. magnetic effect of current
    2. electrostatic effect of current
    3. none of these
    4. heating effect of current

    Answerd

  13. Normally the fuse elements are in parts which are connected in the middle by ten bridge. The melting point of tin bridge is
    1. 88°C
    2. 230°C
    3. 35°C
    4. 540°C.

    Answerb

  14. The voltage across the circuit breaker pole after final current zero is recovery voltage.
    1. false
    2. true

    Answerb

  15. Air circuit breakers are used for voltages above 12 kV.
    1. false
    2. true

    Answera

  16. Double pressure type SF6 circuit breaker is also known as Puffer type.
    1. true
    2. false

    Answerb

  17. Air blast circuit breakers and SF6 circuit breakers are preferred for EHV applications.
    1. true
    2. false

    Answera

  18. Arcing contacts of circuit-breakers are generally made of copper tungsten alloy.
    1. true
    2. false

    Answera

  19. The arc plays important role in the behavior of circuit breaker.
    1. true
    2. false

    Answera

  20. The arc has a brightly burning core of high temperature ranging from 6000 K to 25000 K.
    1. false
    2. true

    Answerb

  21. SF6 is a heavy, colorless and chemically inert gas.
    1. false
    2. true

    Answerb

  22. SF6 gas is electro-positive.
    1. false
    2. true

    Answera

  23. In oil circuit breakers transformer oil is used.
    1. true
    2. false

    Answera

  24. An isolator does not have any current making or current breaking capacity.
    1. true
    2. false

    Answera

  25. SF6 circuit breaker takes minimum time for installation.
    1. true
    2. false

    Answera

  26. A triple pole isolator has three identical poles, with operate simultaneously.
    1. false
    2. true

    Answerb

  27. Isolators operate under no current conditions.
    1. false
    2. true

    Answerb

  28. Non-linear resistors are used in lightning arresters.
    1. false
    2. true

    Answerb

  29. Switching over-voltages are proportional to system voltages.
    1. true
    2. false

    Answera

  30. Switching over-voltages arise from energizing of uncharged line can be reduced by the use of high voltage shunt reactors.
    1. false
    2. true

    Answerb

  31. The damage caused by surge depends on steepness of the wave-front.
    1. false
    2. true

    Answerb

  32. Bulk oil circuit breaker is used for outdoor UHV application.
    1. true
    2. false

    Answerb

  33. In electro-magnetic relays the restraining torque is given by springs.
    1. false
    2. true

    Answerb

  34. For remote operation circuit-must breaker be equipped with shunt trip.
    1. false
    2. true

    Answerb

  35. A protective system which responds to vector difference between two electrical quantities is known as differential protection.
    1. true
    2. false

    Answera

  36. Protective systems prevent faults by disconnecting an equipment in the event of abnormal condition.
    1. false
    2. true

    Answerb

  37. Selectivity
    is the property by virtue of which the protective relaying system
    distinguishes between normal condition and abnormal condition.

    1. true
    2. false

    Answera

  38. Frequency relays are used in generator protection.
    1. false
    2. true

    Answerb

  39. SF6 circuit breaker has high reliability and negligible maintenance.
    1. false
    2. true

    Answerb

  40. Tripping relays are slow and generally attracting armature type.
    1. false
    2. true

    Answera

  41. The over-current relays are connected to the system normally by means of CT’s.
    1. true
    2. false

    Answera

  42. Core balance CT’s are used for earth-fault protection.
    1. false
    2. true

    Answerb

  43. Short circuit tests are conducted on circuit breakers to prove the ratings of the circuit-breakers.
    1. true
    2. false

    Answera

  44. Fusing factor is the ratio of minimum fusing current to the current rating.
    1. true
    2. false

    Answera

  45. The distance protection responds to the ratio V/I.
    1. true
    2. false

    Answera

  46. Graded time lag and grade current over-current protection is used for single radial feeder where time lag can be permitted.
    1. true
    2. false

    Answera

  47. Distance relaying is based on measurement of impedance between relay location and fault point.
    1. false
    2. true

    Answerb

  48. Distance relay is used where time lag can be permitted.
    1. false
    2. true

    Answera

  49. Pilot wire differential relaying is used for lines up to 40 km of length.
    1. false
    2. true

    Answerb

  50. In motor starter, thermal relay provides overload protection as well as single phasing protection.
    1. false
    2. true

    Answerb

  51. Protection against unbalanced supply voltage is provided by negative phase sequence relays.
    1. false
    2. true

    Answerb

  52. Breaking current of a pole on a circuit breaker is the current in that pole at the instant of contact separation.
    1. false
    2. true

    Answerb

  53. Most of the alternators are provided with Buchholz relay in addition to differential protection.
    1. false
    2. tru

    Answera

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Online MCQ EE-Circuit Breakers Part Four
Online MCQ EE-Circuit Breakers Part Two

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