GATE EE 2016 Set 1 — Question 59
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Electrical Machines → Three-Phase Transformers → Auto-Transformer
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Question
A single-phase, 22 kVA, 2200 V/ 220 V, 50 Hz, distribution transformer is to be connected as an auto-transformer to get an output voltage of 2420 V. Its maximum kVA rating as an auto-transformer is
Correct answer
(C) 242
Solution
For a two-winding transformer connected as an auto-transformer, the kVA rating increases.
Given:
Two-winding rating: kVA
Voltage ratio: V / V
Output voltage as auto-transformer: V
This output voltage is obtained by an additive polarity connection: V.
The series winding is the V winding. Its rated current is:
A.
In an auto-transformer, the maximum kVA rating is determined by the rated current of the series winding flowing to the load.
VA = kVA.
Alternatively, using the transformation ratio :
kVA.
Given:
Two-winding rating: kVA
Voltage ratio: V / V
Output voltage as auto-transformer: V
This output voltage is obtained by an additive polarity connection: V.
The series winding is the V winding. Its rated current is:
A.
In an auto-transformer, the maximum kVA rating is determined by the rated current of the series winding flowing to the load.
VA = kVA.
Alternatively, using the transformation ratio :
kVA.
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