The GATE Grind

GATE 2016 EE – Question 59

Electrical Machines · Auto-transformer, Electromechanical energy conversion principles · 2 marks · Multiple choice

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

  1. 22
  2. 24.2
  3. 242
  4. 2420

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (C) 242

Explanation

Connecting the 220 V winding in series with the 2200 V winding gives $2200 + 220 = 2420$ V. The winding current at the 22 kVA rating is $\frac{22000}{220} = 100$ A, and that same 100 A flows out of the 2420 V terminal. The auto-transformer rating is $2420 \times 100 = 242$ kVA.