MCQ

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ELECTRICAL MACHINES

Q11. A 1 KVA, single phase, 50 Hz, 100/250 V transformer gives the following results on short circuit test conducted at high voltage side:
Voltmeter reading: 12.5 V; Ammeter reading: 4 A; wattmeter readin: 80 W.
The equivalent resistance referred to high voltage side will be _______.

Q12. A 3000/300 V transformer takes 0.8 A at power factor of 0.4 on open circuit. Magnetizing current of the transformer will be

Q13. Primary and secondary voltage of autotransformer are 500 V and 400 V repectively. When secondary current is 100 A, calculate % saving of copper

Q14. Calculate core area of 500 kVA , 1-phase, 50 Hz, 6600/5000 V auto transformer, emf per turn = 8 V, maximum flux density 1.3 Wb/square meter

Q15. In a transformer zero voltage regulation at full load is

Q16. A transformer has copper loss of 1.5 % and reactance of 3.5 % when tested on load. If its full load regulation is -0.9 % find its power factor.

Q17. Transformer will operate at maximum efficiency when

Q18. No load efficiency of transformer is________than full load efficiency

Q19. Open circuit and short circuit tests on a 3 kVA, 230 / 230 V, 50 Hz, single phase transformer gave the following results:
OC test: 230 V, 2 A, 100 W
SC test: 15 V, 13 A, 120 W
Determine the efficiency of the transformer at full load and 0.80 power factor lagging.

Q20. A 1000 KVA transformer has an efficiency of 95% at full load and also at 60% of full load, both at unity power factor. Determine the efficiency of the transformer at 80% of full load and unity power factor