Electrical Machines Multiple Choice Questions on “Transformer as a Magnetically Coupled Circuit”.
1. In power transformers, it is found that the iron or core losses practically varies very less, this is because ____________
A. constant core flux
B. constant leakage flux
C. constant leakage and core flux
D. constant load current
Answer: A
Clarification: Due to the constant core flux, the iron losses also remain constant.
2. It is advised to coat the laminations of the core with some enamel, to ensure __________
A. insulation
B. adhesion of laminations
C. reduction in humming sound
D. all of the mentioned
Answer: A
Clarification: It is done to provide insulation.
3. Primary and the secondary winding of the transformer are interlaced mainly for __________
A. reducing leakage flux
B. reducing cost
C. reducing heating
D. saving the copper of the winding
Answer: A
Clarification: Interlacing is done to provide less air gaps and improved efficiency by reduction of leakage fluxes around the core.
4. Transients currents are maximum in the transformer when it is switched on with secondary ______ and when input voltage wave is passing through ________
A. open, zero
B. open, peak
C. closed, zero
D. closed, peak
Answer: A
Clarification: At t=0, the current flowing will be very high as emf is very high due to t = 0.
5. Identify the matching which is not matched correctly?
I. Silicon steel - Power transformer II. Ferrite - High frequency transformers III. Alnico - permanent magnet
A. I, II, III
B. I, III
C. II, I
D. None of the mentioned
Answer: D
Clarification: All are matched correct. High frequency transformer uses ferrites as the magnetic domains reverse very fastly.
6. Identify the matching which is not matched correctly?
I. Silicon steel - Power transformer II. Ferrite - High frequency transformers III. Alnico - permanent magnet
A. I, II, III
B. I, III
C. II, I
D. I
Answer: A
Clarification: All are matched correct. High frequency transformer uses ferrites as the magnetic domains reverse very fastly.
7. Choose the matching which is not matched correctly?
I. Silicon steel - High frequency transformers II. Ferrite - Power transformer III. Alnico - permanent magnet
A. I, II, III
B. I, III
C. II, I
D. III
Answer: C
Clarification: High frequency transformer uses ferrites as the magnetic domains reverse very fastly. And power transformer uses CRGO steel.
8. Which of the following matches are matched correctly?
I. OC test - Copper and iron losses II. SC test - Copper losses III. Load Test - Total losses IV. Sumpner's Test - Iron losses
A. II, III
B. II, III, IV
C. I, IV
D. II, IV
Answer: A
Clarification: OC test gives iron losses. Sumpner’s test gives iron and core losses.
9. In a transformer,eddy-current loss is 1000 watts which is half of the total core loss. If thickness of lamination and frequency are increased by 10%, What is the new core-losses?
A. 3200W
B. 3300W
C. 2200W
D. 3100W
Answer: A
Clarification: Pe = 1000W, Pi = 2000W
Here, V/f = constant
Pe will be same 1000W, Pi = 200+2000 = 2200W
Total core losses = 1000+2200 = 3200W.
10. The voltage conversion ratio of the transformer is inverse of the current transformation.
A. True
B. False
