Transformers

51. N atural air coo ling is generally restricted for transformers up to

1. 1.5 MVA
2. 5 MVA
3. 15 MVA
4. 50 MVA

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52. Natural oil cooling is used for transformers up to a rating of

1. 3000 kVA
2. 1000 kVA
3. 500 kVA
4. 250 kVA

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53. Negative voltage regulation is indicative that the load is

1. capacitive only
2. inductive only
3. inductive or resistive
4. none of the above

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54. Noise level test in a transformer is a

1. special test
2. routine test
3. type test
4. none of the above

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55. No-load current in a transformer

1. lags behind the voltage by about 75°
2. leads the voltage by about 75°
3. lags behind the voltage by about 15°
4. leads the voltage by about 15°

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56. No-load current of a transformer has

1. has high magnitude and low power factor
2. has high magnitude and high power factor
3. has small magnitude and high power factor
4. has small magnitude and low power factor

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57. No-load on a transformer is carried out to determine

1. copper loss
2. magnetising current
3. magnetising current and loss
4. efficiency of the transformer

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58. Open circuit test on transformers is conducted to determine

1. hysteresis losses
2. copper losses
3. core losses
4. eddy current losses

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59. Part of the transformer which is most subject to damage from overheating is

1. iron core
2. copper winding
3. winding insulation
4. frame or case

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60. Power transformers are designed to have maximum efficiency at

1. nearly full load
2. 70% full load
3. 50% full load
4. no load

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