Electrical Machines Questions and Answers – Transformer Losses and Efficiency

This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Transformer Losses and Efficiency”.

1. Which of the statements made here are correct regarding the transformer?

I. Maximum voltage regulation occurs at the leading p.f.
II. Maximum voltage regulation occurs when load p.f. angle and 
impedance angle of the leakage impedance are same.
III. V.R. at zero p.f. is always zero.
IV. V.R. of a transformer may be negative at leading p.f.

a) I, III
b) II, IV
c) 1, III
d) I, IV, III
View Answer

2. Which of the statements made here are correct regarding the transformer?

I. Maximum voltage regulation occurs at the leading p.f.
II. Maximum voltage regulation occurs when load p.f. angle and 
impedance angle of the leakage impedance are same.
III. V.R. at zero p.f. is always zero.
IV. V.R. of a transformer may be negative at leading p.f.

a) I, II, III
b) II, IV
c) 1, III
d) I, IV, III
View Answer

3. Which of the statements made here are incorrect regarding the transformer?

I. Maximum voltage regulation occurs at the leading p.f.
II. Maximum voltage regulation occurs when load p.f. angle and 
impedance angle of the leakage impedance are same.
III. V.R. at zero p.f. is always zero.
IV. V.R. of a transformer may be negative at leading p.f.
  

a) I,III
b) II,IV
c) 1,III
d) I,IV,III
View Answer

4. Which of the statements made here are incorrect regarding the transformer?

I. Maximum voltage regulation occurs at the leading p.f.
II. Maximum voltage regulation occurs when load p.f. angle and 
impedance angle of the leakage impedance are same.
III. V.R. at zero p.f. is always zero.
IV. V.R. of a transformer may be negative at leading p.f.

a) I,II,III
b) IV
c) 1,III
d) I,IV,III
View Answer

5. Which of the following mentioned losses occur in a transformer?
a) Hysteresis losses; Eddy current losses; Dielectric losses; Stray load losses
b) Hysteresis losses; Eddy current losses;
c) Dielectric losses; Stray load losses
d) Hysteresis losses; Eddy current losses; Stray load losses
View Answer

6. Mutual flux ______ at the lagging loading and it _____ at the leading power factor.
a) decreases, increases
b) increases, increases
c) decreases, decreases
d) increases, decreases
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7. It is possible to attain maximum efficiency in a transformer when the ______
a) core losses are equal to rated full load copper losses
b) core losses are more than rated full load copper losses
c) core losses and full load copper losses are constant
d) copper loss also becomes constant
View Answer

8. The efficiency of a 20 KVA, 2000/200 V, single phase transformer at unity pf is 98%. The total losses at this condition is?
a) 408W
b) 4.08kW
c) 204W
d) 2.04kW
View Answer

9. The efficiency of a 20 KVA, 2000/200 V, single phase transformer at unity pf is 98%. The given total losses at full load is 200 W. The pu resistance is?
a) 0.01
b) 0.1
c) 1.0
d) 0.0196
View Answer

10. The load current at which maximum efficiency occurs is independent of the load power factor.
a) True
b) False
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11. The full load voltage drop in a 1-phase transformer is 2% and 4% respectively due to resistance and leakage reactance. Then the voltage drop is maximum at __________
a) 0.45 lagging
b) 0.45 leading
c) 0.9 lagging
d) 0.9 leading
View Answer

12. The full load voltage drop in a 1-phase transformer is 2% and 4% respectively due to resistance and leakage reactance. Then the voltage drop is zero at __________
a) 0.45 lagging
b) 0.45 leading
c) 0.9 lagging
d) 0.9 leading
View Answer

13. Core losses of a transformer as a function of frequency is best approximated by which of the below characteristics?
a)
b)
c)
d)
View Answer

14. From the above graph of the core losses per cycle is, the hysteresis losses per phase for a transformer at a operating frequency of 40 Hz is?

a) 20W
b) 30W
c) 80W
d) 32W
View Answer

15. From the above graph of the core losses per cycle is, the eddy losses per phase for a transformer at a operating frequency of 40 Hz is?

a) 15 W
b) 20W
c) 35W
d) 32W
View Answer

16. The efficiency of a transformer can be calculated accurately from ___________
a) Open circuit test, Short circuit test
b) Open circuit test, Short circuit test, Sumpner’s test
c) Sumpner’s test
d) load test
View Answer

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