Transformers

11. A transformer transforms

1. voltage
2. current
3. power
4. frequency

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12. An ideal transformer is one which has

1. no losses and magnetic leakage
2. interleaved primary and secondary windings
3. a common core for its primary and secondary windings
4. core of stainless steel and winding of pure copper metal

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13. An ideal transformer will have maximum efficiency at a load such that

1. copper loss = iron loss
2. copper loss < iron loss
3. copper loss > iron loss
4. none of the above

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14. An open-circuit test on a transformer is conducted primarily to measure

1. insulation resistance
2. copper loss
3. core loss
4. total loss

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15. Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is

1. approximately equal to one
2. less than one
3. great than one
4. none of the above

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16. Buchholz's relay gives warning and protection against

1. electrical fault inside the transformer itself
2. electrical fault outside the transformer in outgoing feeder
3. for both outside and inside faults
4. none of the above

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17. Delta/star transformer works satisfactorily when

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

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18. Distribution transformers are generally designed for maximum efficiency around

1. 90% load
2. zero load
3. 25% load
4. 50% load

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19. During open circuit test of a transformer

1. primary is supplied rated voltage
2. primary is supplied full-load current
3. primary is supplied current at reduced voltage
4. primary is supplied rated kVA

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20. During short circuit test iron losses are negligible because

1. the current on secondary side is negligible
2. the voltage on secondary side does not vary
3. the voltage applied on primary side is low
4. full-load current is not supplied to the transformer

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