Electrical Machines Multiple Choice Questions 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
Answer: B
Clarification: V.R. is always negative at leading p.f. and the load p.f. angle and impedance angle of the leakage impedance should be same for maximum V.R.
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
Answer: A
Clarification: V.R. is always negative at leading p.f. and the load p.f. angle.
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
Answer: A
Clarification: V.R. is always negative at leading p.f. and the load p.f. angle and impedance angle of the leakage impedance should be same for maximum V.R.
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
Answer: B
Clarification: V.R. is always negative at leading p.f. and the load p.f. angle.
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
Answer: A
Clarification: Hysteresis losses-due to magnetic material; Eddy current losses-on the core area; Dielectric losses- due to insulation material; Stray load losses- due to leakage through the parts of the transformer.
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
Answer: A
Clarification: The mutual flux falls when the transformer is working at lagging p.f. and it increases at leading p.f.
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