GATE 2015 EE – Question 60
A 200/400 V, 50 Hz, two-winding transformer is rated at 20 kVA. Its windings are connected as an auto-transformer of rating 200/600 V. A resistive load of $12\ \Omega$ is connected to the high voltage (600 V) side of the auto-transformer. The value of equivalent load resistance (in Ohm) as seen from low voltage side is ________.
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Correct answer: 1.3 to 1.4
Explanation
The auto-transformer has a voltage ratio of $\frac{600}{200} = 3$. A load seen from the low voltage side is divided by the square of the ratio, so $\frac{12}{3^2} = \frac{12}{9} = 1.33\ \Omega$.