## Sunday, April 14, 2013

### Transformers Objective Questions: Part-8

[1] The degree of mechanical vibrations produced by the laminations of a transformers depends on
A. Tightness of clamping
B. Gauge of laminations
C. Size of laminations
D. All of the above

[2] The no-load current drawn by transformer is usually........percent of the full-load current?
A. 0.2 to 0.5 %
B. 2 to 5%
C. 12 to 15 %
D. 20 to 30 %

[3] The dielectric strength of transformer oil is expected to be
A. 1kV
B. 33kV
C. 100kV
D. 330 kV

[4] During the short-circuit test on a small transformer the frequency is increased from 50-200Hz. The copper losses will increase by a factor of
A. 16
B. 4
C. 1
D. 1/4

[5] No-load current in a transformer
A. Lags behind the voltage by about 75 deg
C. Lags behind the voltage by about 15

[6] While conducting short-circuit test on a transformer the following side is short circuited
A. High voltage side
B. Low voltage side
C. Primary side
D. Secondary side

[7] The chemical used in breather for transformer should have the quality of
A. Ionizing air
B. Absorbing moisture
C. Cleansing the transformer oil
D. Cooling the transformer oil

[8] If a pump motor is run on 2/3rd of its supply voltage, it will
A. Continue to deliver same power
B. Burn
C. Stall
D. Continue to run at lower speed

[9] An ideal transformer has infinite values of primary and secondary inductances. The statement is
A. True
B. False

[10] The noise resulting from vibrations of laminations set by magnetic force, is termed as
A. Magnetostriction
B. Boo
C. Hum
D. Zoom

12:35 AM

1. During the short-circuit test on a small transformer the frequency is increased from 50-200Hz. The copper losses will increase by a factor of ........
how the factor is 16?

1. Pcu is directly proportional to square of frequency

2. Thanks for such gud questions *

3. the low voltage of a 400/230 V single phase 50Hz transformer is to be connected to keep the magnetization current at the same level in both cases the voltage of 25Hz should be