221. The iron loss in a 100 KVA transformer is 1 KW and full load copper losses are 2 KW. The maximum efficiency occurs at a load of

- 100 KVA
- 70.7 KVA
- 141.4 KVA
- 50 KVA

222. In a 1-phase transformer, the copper loss at full load is 600 Watts. At half of the full load, the copper loss will be

- 150Watts
- 75 Watts
- 600 Watts
- 300 Watts

223. The high-voltage and low-voltage winding resistances of a distribution transformer of 100 KVA, 1100/220 volts. 50Hz are 0.1 Ω and 0.004 Ω respectively. The equivalent resistances referred to high-voltage side and low-voltage side are respectively.

- 2.504 Ω and 0.2 Ω
- 0.2 Ω and 0.008 Ω
- 0.10016 Ω and 2.504 Ω
- 0.008 Ω and 0.10016 Ω

224. If the frequency of input voltage of a transformer is increased keeping the magnitude of the voltage unchanged, then

- Both hysteresis loss and eddy current loss in the core will increase.
- Hysteresis loss will increase but eddy current loss will decrease.
- Hysteresis loss will increase but eddy current loss will remain unchanged
- Hysteresis loss will decrease but eddy current loss will increase

225. A 10 ohm resistive load is to be impedance matched by a transformer to a source with 6250 Ω of internal resistance. The ratio of primary to secondary turns of the transformer should be

- 15
- 20
- 25
- 10

226. Low voltage windings are placed near to the core in the case of concentric windings because

- It reduces hysteresis loss
- It reduces eddy current loss
- It reduces insulation requirement
- It reduces leakage fluxes

227. A stepped core is used in transformers in order to reduce

- Volume of iron
- Volume of copper
- Iron loss
- Reluctance of core

228. When a 400-Hz transformer is operated at 50Hz, its rating is

- Reduced to 1/8
- Increased 8 times
- Unaffected
- Increased 64 times

229. The rating of a transformer is expressed in

- KVA
- KW
- HP
- W

230. Short circuit test on transformer is conducted to obtain

- Core losses at any load
- Hysteresis loss only
- Ohmic loss
- Eddy current loss only

231. Total losses occurring in a transformer when it is operating at its maximum efficiency are 2000 W. The total copper losses at this load are

- 2000 W
- 1000 W
- 1500 W
- 800 W

232. One 200 V, 100 W bulb is connected in series with primary of a 200 V, 10 KVA transformer. If its secondary is left open-circuited then the bulb would have

- Full brightness
- Poor brightness
- A little less than full brightness
- More than full brightness

233. The primary to secondary turns ratio of a transformer is 1 : 2. If the primary is connected to 50 Hz supply, then the frequency of secondary supply in Hz is

- 50 Hz
- 25 Hz
- 100 Hz
- 150 Hz

234. Buchholz relay is used on

- Welding transformers
- Air-cooled transformers
- Furnace transformers
- Oil cooled transformers

235. The power transformer is a constant

- Voltage device
- Current device
- Power device
- Main flux device

236. No-load test on a transformer is carried out to determine

- Copper loss
- Magnetizing current
- Magnetizing current and loss
- Efficiency

237. The equivalent resistance of the primary of a transformer whose transformation ratio is 5 and resistance is 0.1 Ω. When referred to the secondary will be

- 0.5 Ω
- 2.5 Ω
- 0.02 Ω
- 0.004 Ω

238. A transformer steps up or down

- a.c. only
- d.c. only
- either a.c. or d.c.
- a.c. mixed with d.c.

239. When power is drawn from a secondary coil of the transformer, the dynamic resistance

- Increases
- Decreases
- Remains constant
- Changes erratically

240. Distribution transformers have core losses

- More than full load copper losses
- Equal to full load copper losses
- Less than full load copper losses
- Negligible compared to full load copper losses