1.The secondary
winding of which of the following transformers is always kept closed?
A. Current
transformer
B. Voltage
transformer
C. Power
transformer
D. Step
down transformer
Answer & Solution
Answer: A
Explanation:
If the current transformer secondary is not shorted
when unused and kept open then it can develop a very high voltage across
secondary which may damage transformer insulation.
2. If the supply frequency of a transformer increases, the secondary output voltage of the transformer
A. Increase
B. Decrease
C. Remain
the same
D. Any
of the above
Answer & Solution
Answer: C
Explanation:
The transformer is a static device that changes
Voltage from one side of its coil to the other at a constant frequency.
Frequency
does not change because of the working principle of the transformer-based
on Mutual induction which happens without any change in
frequency.
3. Power transformers are designed to have maximum efficiency at
A. Full
load
B. 50%
load
C. 80%
load
D. No
load
Answer & Solution
Answer: A
Explanation:
Power
transformers are used for transmission as a step-up device hence
they are not directly connected to consumers therefore, load fluctuation is very less. So the power
transformer can operate on full load.
4. The open-circuit test in a transformer is used to measure
A. Copper
loss
B. Winding
loss
C. Total
loss
D. Core
loss
Answer & Solution
Answer: A
Explanation:
As the transformer is open-circuited there is no
output. So the copper loss is neglected as the no-load current is very less.
5. The leakage flux in a transformer depends upon the value of
A. Frequency
B. Mutual
Flux
C. Load
current
D. Applied
Voltage
Answer & Solution
Answer: A
Explanation:
- In a Transformer, Core flux is the difference between primary flux
and Secondary flux which are opposite to each other in direction.
- So, some of the primary flux passes through the core, and the
remaining becomes leakage flux (Because Secondary flux forces it to get
out of the core).
- The same is the case with Secondary flux. Now, flux is directly
proportional to Voltage and Current.
When
Current increases due to increased load (and voltage remains the same). Then
both primary and secondary flux increase. Because both of them increases, so
their difference remains the same. And all remaining flux is forced out. Hence
leakage flux increases with current, but Core flux remains
constant.