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Electrical Engineering Objective Questions { Transformers }

71. A transformer has Ni and N2 turns in primary and secondary windings respectively. Its secondary windings reactance of x2 LI, when referred to primary, is
A. x,,
B. x2?1
C. N
D. N2

72.  A good voltage regulation of a transformer means
A. difference between primary and secondary voltage is least
B. difference between primary and secondary voltage is maximum
C. output voltage fluctuation with power factor is the least
D. output voltage fluctuation form no load to full load is least.

73. Match the items on the left side with the most appropriate item on the right side and select the correct answer from the codes given below the lists : Type,Application (A) circuits (B) Distribution trans-,(Q) Impedance former matching (C) Pulse transformer ,(R) At different localities of a city (D) Audio-frequency,(S) At generating transformer. Power,(P) Thyristor firing transformer
A. A?P, B?Q, C?R, D?S
B. A?S, B?R, C?Q, D?P
C. A?S, B?R, C?P, D?Q
D. A?R, B?S, C?P, D?Q

74.  Open-circuit test on a single-phase transformer gave the following data : 230 V at 50 Hz, 2 A, p.f. = 0.2 lag. If open-circuit test is performed at 230 V, 45 Hz, then no-load current is
A. decreased at pl. > 0.2
B. decreased at p.f. <0.2
C. increased at p.f. > 0.2
D. increased at pl. <0.2

75. Test used to determine the efficiency of two identical transformers at full load is
A. Open-circuit test
B. Short circuit test
C. Type tests
D. Back to back test

76. A 220/115 V, 25 Hz, 1-phase transformer has eddy current loss of 100 watt which is half of the no-load loss at rated applied voltage. If this transformer is used with primary connected to a 440 V, 50 V, 50 Hz mains, the total no-load loss would be
A. 300 W
B. 600 W
C. 1000 W
D. 400 W

77. If Cu loss of a transformer at 7/8th full load is 4900 W, then its full-load Cu loss would be
A. 5600 watts
B. 6400 watts
C. 375 watts
D. 429 watts

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