# Transformer MCQ Questions

### 1. In a power transformer

(a) primary winding is closer to core
(b) secondary winding is closer to core
(c) low voltage winding is closer to core
(d) high voltage winding is closer to core

Answer: (c) low voltage winding is closer to core

### 2. In a transformer, the magnetic coupling between primary and secondary circuit can be increased by

(a) increasing the number of turns
(b) using soft material for windings
(c) using the magnetic core of low reluctance
(d)using transformer oil of batter quality.

Answer: (c) using the magnetic core of low reluctance

### 3. If the flux density in the core of a transformer is increased

(a) frequency of secondary winding will change
(b) wave shape on secondary side will be distorted
(c) size of transformer can be reduced
(d) eddy current loss will reduce.

Answer: (c) size of transformer can be reduced

### 4. If the supply frequency is increased keeping voltage constant

(a) eddy current losses will decrease
(b) hysteresis losses will decrease
(c) eddy current losses will remain unchanged
(d) hysteresis losses will remain unchanged.

Answer: (c) eddy current losses will remain unchanged

### 5. At no load, the current taken by a transformer

(a) lags behind the applied voltage by 80 degree
(b) lags behind the applied voltage by 50 degree
(c) leads the applied voltage by 80 degree
(d) leads the applied voltage by 50 degree.

Answer: (a) lags behind the applied voltage by 80 degree

(a) 15
(b) 30
(c) 50
(d) 2500

(a) 800 kVA
(b) 400 kVA
(c) 200 kVA
(d )100 kVA

### 8. Leakage flux of a transformer may be minimized by

(a) sectionalizing and interleaving the primary and the secondary windings
(b) constantly cooling the core
(c) under rating the transformer
(d) reducing the reluctance of the iron core to the minimum.

Answer: (a) sectionalizing and interleaving the primary and the secondary windings.

### 9. Power transformers are usually designed to have maximum efficiency

(b) at 75% of full load
(c) at 50% of full load
(d) between 50% and 75% of full load.

### 10. Distribution transformers are usually designed to have maximum efficiency

(b) at 75% of full load
(c) near 50% of full load
(d) between 50% and 75% of full load.

### 11. In a transformer it is difficult to measure the efficiency by output-input measurement method because

(a) the output is sinusoidal and hence cannot be measure
(b) losses are abnormally high
(c) efficiency of transformer is usually high and hence extremely accurate measurements will be necessary
(d) output is out of phase with respect to input.

Answer: (c) Efficiency of transformer is usually high and hence extremely accurate measurements will be necessary.

### 12. The leakage flux in a transformer depends upon

(c) load current, voltage and frequency
(d) load current, voltage, frequency and power factor.

### 13. What is maximum order of flux density used in cores using CRGO sheets

(a) 0.04 webers/m2
(b) 0.4 webers/m2
(c) 1.04 webers/m2
(d) webers/m2

### 14. The phase difference between the primary and the secondary voltage of a transformer is

(a) 0 degree
(b) 180 degree
(c) 90 degree
(d) between 30 degree and 60 degree

### 15. The desirable properties of transformer core material is

(a) low permeability and low hysteresis loss
(b) high permeability and high hysteresis loss
(c) low permeability and high hysteresis loss
(d) high permeability and low hysteresis loss

Answer: (d) high permeability and low hysteresis loss

(a) 6400 W
(b) 1600 W
(c) 800 W
(d) 400 W

(a) 1 kVA
(b) 5 kVA
(c) 50 kVA
(d) 500 kVA

### 18. Operating time of Buchholz relay is in the order of

(a) 0.1 micro second
(b) 0.1 milli second
(c) 0.1 second
(d) 1 second

### 19. For a transformer, operating at a constant load current, maximum efficiency will occur at

(a) Zero power factor
(b) unity power factor
(d) 0.8 lagging power factor.

### 20. “A” class insulation can withstand

(a) temperature rise of 105 degree Celsius
(b) maximum temperature rise of 105 degree Celsius
(c) temperature gradient of 105 degree Celsius
(d) heating rate of 105 Celsius in 24 hours.

Answer: (b) maximum temperature rise of 105 degree Celsius

(a) Transmission
(b) Substation
(c) Generator
(d) Distribution

(a) 0.4
(b) lagging
(d) unity

(b) lagging
(c) 0.8
(d) unity

### 24. When a delta connected primary of a 3-phase transformer is connected to 3-phase supply

(a) magnetizing current in phase winding will carry third harmonics but line current will be free from it.
(b) magnetizing current in phase winding will contain third harmonica and line current will also contain third harmonics.
(c) magnetizing current will not contain third harmonics but line current will contain third harmonics.
(d) none of the above.

Answer: (a) magnetizing current in phase winding will carry third harmonics but line current will be free from it.

### 25. Scott connections are used to convert

(a) three-phase supply to D.C. supply
(b) three-phase supply to three-phase supply
(c) three-phase supply to two-phase supply
(d) three-phase supply to single-phase supply

Answer: (c) three-phase supply to two-phase supply

(a) star/delta
(b) delta/star
(c) star/star
(d) delta/delta.

### 27. Delta-delta power transformer is protected by current transformer having

(a) star/star connections
(b) delta/delta connections
(c) star/delta connections
(d) delta/star connections

### 28. Star-star power transformer is protected by current transformer having

(a) star/star connections
(b) delta/delta connections
(c) star/delta connections
(d) delta/star connections