Hi friends, this post is about transformer objectives. These are some of the questions asked in previous question papers of Gate, IES and other competitive exams. check out and comment if you have any doubts.....
1) Primary winding of a transformer comprises of two identical winding in parallel. If one winding is removed, magnetizing current will be
A) halved
B) the same
C) doubled
D) increased four times
Ans:C
2) If a sinusoidal voltage source is connected to a power transformer its no load current would be
A) sinusoidal and lagging the voltage by 90°
B) sinusoidal and lagging the voltage by less than 90°
C) rich in third harmonic and its fundamental would lag the voltage by 90°
D) rich in third harmonic and its fundamental would lag the voltage by less than 90°
Ans:D
3) If in a transformer core, a material having high reluctance path but having same hysteresis loop is employed
A) Ie will increase
B) Im will increase
C) Im will decrease
D) both Im and Ie will increase
Ans:B
4) A transformer steps up the voltage by a factor 100. The ratio of current in the primary to that in the secondary is
A) 1
B) 100
C) 0.01
D) 0.1
Ans:B
5) If the applied voltage of a certain transformer is increased by 50% and the frequency is reduced to 50% (assuming that the magnetic circuit remains unsaturated), the maximum core flux density will
A) change to three times the original value
B) change to 1.5 times the original value
C) change to 0.5 times the original value
D) remain the same as the original value
Ans:A
6) The low voltage winding of a 400/230 V single phase 50 HZ transformer is to be connected to a 25 HZ supply. In order to keep the magnetization current at the same level in both the cases the voltage at 25 HZ should be
A) 230 V
B) 460 V
C) 115 V
D) 65 V
Ans:C
7) At 50 HZ operation, a single phase transformer has hysteresis loss of 200 W and eddy current loss of 100 W. Its core loss at 60 HZ operation will be
A) 432 W
B) 408 W
C) 384 W
D) 360 W
Ans:C
8) The primary ampere turns are counter balanced by
A) secondary ampere-turns
B) primary flux
C) increase in mutual flux
D) increase in secondary current
Ans:A
9) The transformer exciting current has two components, magnetizing component and core-loss component. Neglecting impedance drop
A) both of them are in phase with the supply voltage
B) the former lags the supply voltage by 90° while the latter is in phase with supply voltage
C) both of them lag the supply voltage by 90°
D) the former is in phase with the supply voltage while the latter lags the supply voltage by 90°
Ans:B
10) A single-phase transformer when supplied from 220 V, 50 HZ has eddy current loss of 50 W. If the transformer is connected to a voltage of 330 V, 50 HZ, the eddy current loss will be
A) 168.75 W
B) 112.5 W
C) 75 W
D) 50 W
Ans:B
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