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GATE 2015 EE – Question 32

Electrical Machines · Single phase transformer: equivalent circuit, phasor diagram, open circuit and short circuit tests, regulation and efficiency · 1 mark · Multiple choice

The self inductance of the primary winding of a single phase, 50 Hz, transformer is 800 mH, and that of the secondary winding is 600 mH. The mutual inductance between these two windings is 480 mH. The secondary winding of this transformer is short circuited and the primary winding is connected to a 50 Hz, single phase, sinusoidal voltage source. The current flowing in both the windings is less than their respective rated currents. The resistance of both windings can be neglected. In this condition, what is the effective inductance (in mH) seen by the source?

  1. 416
  2. 440
  3. 200
  4. 920

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Correct answer: (A) 416

Explanation

With the secondary short circuited, the inductance seen at the primary is $L_1 - \frac{M^2}{L_2} = 800 - \frac{480^2}{600} = 800 - 384 = 416$ mH.