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MCQs 1: The globules of water present in oil may result directly in a breakdown. This can be prevented by

Proper insulation Isolation of oil from air by using an inert gas Heating the tank None of these
Answer Explanation

MCQs 2: In a transformer tank, grounding is given to protect it from lightening stoke. Grounding lug is usually installed near

Bottom of the tank Top of the tank In the middle of the tank Anywhere on the tank
Answer Explanation

MCQs 3: For the calculation of induced emf in a transformer the flux used in the equation is in its

RMS value Average value Maximum value Double of its maximum value
Answer Explanation

MCQs 4: If the primary winding is excited by a purely sinusoidal alternating voltage, than the nature of the flux produced is

Square wave Rectangular wave Saw tooth wave Sinusoidal wave
Answer Explanation

MCQs 5: A transformer is said to be isolation transformer if its primary to secondary ratio is

Equal to one More than one Less than one Equal to 0.5
Answer Explanation

MCQs 6: A 5kV / 250V, 50Hz single phase core type transformer with average flux in the core is 0.05wb. The number of turns in the primary winding is

273 278 280 287
Answer Explanation

MCQs 7: If V1 is the primary applied voltage and E1 is the primary induced emf. For an ideal transformer

V1 > E1 V1 = E1 V1 < E1 V1 = E1 / 2
Answer Explanation

MCQs 8: For an ideal transformer winding resistances and leakage flux should be

Least, maximum Both should be maximum Both should be zero Maximum, least
Answer Explanation

MCQs 9: When a resistance is to be transferred from primary to secondary side of transformer with the turns ratio as k, it must be

Multiplied by k ∧ 2 Multiplied by k Divided by k Divided by k ∧ 2
Answer Explanation

MCQs 10: If the power factor of load is near unity and leading, the full load voltage regulation of a power transformer will be

Zero One 0.5 0.707
Answer Explanation

MCQs 11: If the applied voltage of a certain transformer is increased by 50% keeping the frequency constant, the maximum flux density will become

Remains same 1.5 times the original value Double the original value Half of the original value
Answer Explanation

MCQs 12: A 10 kVA, 2000 / 100v transformer has R1=1.5 ohm, R2=0.005 ohm, X1=2.5 ohm and X2=0.08 ohm. The equivalent resistance referred to primary is

3 ohm 3.25 ohm 3.5 ohm 3.8 ohm
Answer Explanation

MCQs 13: If the supply voltage is kept at constant value and the supply frequency is increased. The magnetizing and core loss component

Both will decrease Magnetizing component will increase and core loss will decrease Magnetizing component will decrease and core loss will increase Both will increase
Answer Explanation

MCQs 14: For a certain transformer if E1 is the emf across primary winding, E2 is the emf across secondary winding and K is the ratio of secondary to primary turns. The value of secondary emf referred to the primary side is

E2 / K E2 / K ∧ 2 K * E2 K ∧ 2 * E2
Answer Explanation

MCQs 15: If the voltage supply of a single phase transformer is doubled and the supply frequency is halved, then the eddy current loss will become

remains same double of the original four times of original half of the original
Answer Explanation

MCQs 16: For a single phase no load transformer, which among the following losses will be minimum?

hysteresis losses eddy current losses copper losses mechanical losses
Answer Explanation

MCQs 17: In the design of transformer, higher flux density is used. Due to which

weight per kVA increases weight per kW increases weight per kW decreases weight per kVA decreases
Answer Explanation

MCQs 18: If the applied voltage is increased by 10% and the applied frequency is increased by 20% of a single phase transformer, the percentage change in eddy current losses will be

19% 20% 21% 40%
Answer Explanation

MCQs 19: A 600kVA transformer has core losses of 1w at 25 Hz and 2.5w at 50 Hz (neglecting resistances and assuming flux density to be constant). The power required at 60 Hz is

3 watt 3.5 watt 3.24 watt 3.54 watt
Answer Explanation

MCQs 20: What happens to the hysteresis losses and eddy current losses, if the frequency of a transformer is increased keeping the supply voltage constant?

Both will decrease Hysteresis losses will increase and eddy current losses will decrease Hysteresis losses will remain same and eddy current losses will decrease Hysteresis losses will decrease and eddy current losses will remain same
Answer Explanation

MCQs 21: For maximum efficiency in a transformer

Core losses = 2 * copper losses Core losses = copper losses / 2 Core losses = copper losses Core losses = copper losses ∧ 2
Answer Explanation

MCQs 22: If the power factor of a transformer increases, then its efficiency will

Increases Decreases Remains constant Not related to each other
Answer Explanation

MCQs 23: A 600 kVA transformer has iron losses of 400 kW and copper losses of 500 kW. Its kVA rating for maximum efficiency is given by

537 kVA 548 kVA 555 kVA 585 kVA
Answer Explanation

MCQs 24: In a 20 kVA, 2200 / 220 volts transformer iron and copper losses are 300 and 400 watts respectively. Its efficiency at half load and unity power factor is

95.11% 96.15% 97.77% 98%
Answer Explanation

MCQs 25: A 500 kVA single phase transformer has 90% efficiency at both half load and full load at unity power factor. Then iron losses will be

12.55 KW 13.55 kW 16.55 kW 18.55 KW
Answer Explanation

MCQs 26: If the magnitude of leakage reactance is equal to the resistance of both primary and secondary of a single phase transformer. Then the input power factor is

1 / √2 1 √2 zero
Answer Explanation

MCQs 27: Open circuit test is to be performed on transformer to find

Constant losses Copper losses Both (a) and (b) None of these
Answer Explanation

MCQs 28: If the transformer is step - up transformer then for performing short circuit test meter is connected to the

H.V. side L.V. side Any side Test cannot be performed on step up t / f
Answer Explanation

MCQs 29: If short circuit test is performed on the transformer with constant rated voltage and increased frequency, then the short circuit current and power factor

Both will increase Both will decrease Increase, decrease Decrease, remains constant
Answer Explanation

MCQs 30: Which test is also called as back to back test?

Retardation test Sumpner’s test Field test Voltage drop test
Answer Explanation

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