Transformer MCQs Part 15
Contents
- 1 If Zs and Zp are secondary and primary load impedances of a step-up transformer, then which of following is correct
- 2 Iron core is provided in transformer so as to
- 3 The auto-transformer is preferred in situations where the voltage transformation ratio (K) is
- 4 The no-load ratio of a 50 Hz single phase transformer is 6000/220 V. The value of flux in core is 0.06 Wb. What is the number of primary turns
- 5 Usually, transformers with rating less than 5 kVA are
If Zs and Zp are secondary and primary load impedances of a step-up transformer, then which of following is correct
If Zs and Zp are secondary and primary load impedances of a step-up transformer, then which of following is correct:
- Zp < Zs
- Zp > Zs
- Zp = Zs
- Insufficient data
Correct answer: 1. Zp < Zs
Explanation: Zp = (N1 / N2) ^2 * Zs
Since N2 > N1; Zp < Zs
Iron core is provided in transformer so as to
Iron core is provided in transformer so as to:
- Reduce core losses
- Increase its weight
- Proivde tight magnetic copling
- None of these
Correct answer: 3. Provide tight magnetic coupling
Explanation: Iron core in transformer ensures that tight magnetic coupling is present between two windings. In case of practical transformer, the coefficient of coupling can be as high as 0.99
The auto-transformer is preferred in situations where the voltage transformation ratio (K) is
The auto-transformer is preferred in situations where the voltage transformation ratio (K) is:
- Very high
- Very low
- Unity
- Near unity
Correct answer: 4. Near unity
Explanation:
Wa = (1 – K) Wo
Where
Wa = Wt of Cu in autotransformer
Wo = Wt of Cu in ordinary transformer
Saving in Cu = Wo – Wa = kWo
If K = 0.1 saving of Cu is only 10%
However, If K = 0.8, saving of Cu is 80%, the higher the K is, the greater is saving of Cu.
Therefore the nearer the value of K to 1, the greater is the saving of Cu.
The no-load ratio of a 50 Hz single phase transformer is 6000/220 V. The value of flux in core is 0.06 Wb. What is the number of primary turns
The no-load ratio of a 50 Hz single phase transformer is 6000/220 V. The value of flux in core is 0.06 Wb. What is the number of primary turns
- 10
- 12
- 17
- 26
Correct answer: 17
From formula: Es = 4.44 * f * Ns * Φm
220 = 4.44 * 50 * Ns *0.06
Ns = 17
Usually, transformers with rating less than 5 kVA are
Usually, transformers with rating less than 5 kVA are:
- Natural air cooled
- Oil cooled
- Water cooled
- None of these
Correct answer: 1. Natural air cooled