Transformers

61. Power transformers are generally designed to have maximum efficiency around

1. no-load
2. half-load
3. near full-load
4. 10% overload

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62. Primary winding of a transformer

1. is always a low voltage winding
2. is always a high voltage winding
3. could either be a low voltage or high voltage winding
4. none of the above

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63. Reduction in core losses and increase in permeability are obtained with transformer employing

1. core built-up of laminations of cold rolled grain oriented steel
2. core built-up of laminations of hot rolled sheet
3. either of the above
4. none of the above

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64. Short 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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65. Silicon steel used in laminations mainly reduces

1. hysteresis loss
2. eddy current losses
3. copper losses
4. all of the above

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66. Spacers are provided between adjacent coils

1. to provide free passage to the cooling oil
2. to insulate the coils from each other
3. both (a) and (b)
4. none of the above

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67. Star/star transformers work satisfactorily when

1. load is unbalanced only
2. load is balanced only
3. on balanced as well as unbalanced loads
4. none of the above

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68. Sumpner's test is conducted on trans-formers to determine

1. temperature
2. stray losses
3. all-day efficiency
4. none of the above

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69. The changes in volume of transformer cooling oil due to variation of atmospheric temperature during day and night is taken care of by which part of transformer

1. Conservator
2. Breather
3. Bushings
4. Buchholz relay

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70. The chemical used in breather for transformer should have the quality of

1. ionizing air
2. absorbing moisture
3. cleansing the transformer oil
4. cooling the transformer oil.

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