Transformer MCQ Questions and Answers

181. Which parameter does not change during transformation action in a transformer?

1. Voltage
2. Frequency
3. Current
4. None of these

182. A 10 kVA, 400V/200V, single-phase transformer with 10% impedance, draws a steady short circuit current of

1. 50 A
2. 150 A
3. 250 A
4. 350 A

183. The transformer laminations are insulated from each other day

1. Mica strip
2. Thin coat of varnish
3. Paper
4. Any of the above

184. Iron loss of a transformer can be measured by

1. Low power factor wattmeter
2. Unity power factor wattmeter
3. Frequency meter
4. Any type of wattmeter

185. In an actual transformer, the iron loss remains practically constant from no load to full load because

1. Value of transformation ratio remains constant
2. Permeability of transformer core remains constant
3. Core flux remains practically constant
4. Primary voltage remains constant

186. In the supply frequency to the transformer is increased, the iron loss will

1. Not change
2. Decrease
3. Increase
4. Any of the above

187. When a given transformer is run at its rated voltage but the reduced frequency, its

1. Flux density remains unaffected
2. Iron losses are reduced
3. Core flux density is reduced
4. Core flux density is increased

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

1. No-load
2. Half-load
3. Near full-load
4. 10% overload

189. Which winding of the transformer has less cross-sectional area?

1. Primary winding
2. Secondary winding
3. Low voltage winding
4. High voltage winding

190. Two transformers operating in parallel will share the load depending upon their

1. Leakage reactance
2. Per unit impedance
3. Efficiencies
4. Ratings

191. Two power transformer is a constant

1. Voltage device
2. Current device
3. Power device
4. Main flux device

192. The purpose of providing iron core in a step-up transformer is

1. To provide coupling between primary and secondary
2. To increase the magnitude of mutual flux
3. To decrease the magnitude of magnetizing current
4. To provide all the above features

193. The no-load current of a transformer

1. Has high magnitude and low power factor
2. Has high magnitude and high power factor
3. Has small magnitude and high power factor
4. Has small magnitude and low power factor

194. Transformer breathes in when

1. Load on it increases
2. Load on it decreases
3. Load remains constant
4. None of the above

195. 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

196. 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

197. The degree of mechanical vibrations produced by the laminations of a transformer depends on

1. Size of laminations
2. Gauge of laminations
3. Tightness of clamping
4. All of the above

198. A transformer is connected to a constant voltage supply. As the supply frequency increases, what happens to the magnetic flux in the core?

1. Decreases
2. Increases towards saturation
3. Becomes zero
4. Become constant

199. The efficiency of a transformer at full load, 0.8 pf lagging is 95%. What will its efficiency at full load, 0.8 pf leading be?

1. 85 %
2. 90 %
3. 95 %
4. 100 %

200. When a sinusoidal exciting current is applied to a transformer, what is the mutual flux produced?

1. Flat tap
2. Sinusoidal
3. Zero
4. Second harmonic only