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GATE 2014 EE (EE1) – Question 46

Electrical Machines · Types of losses and efficiency calculations of electric machines · 2 marks · Multiple choice

The core loss of a single-phase 230/115 V, 50 Hz transformer is measured from the 230 V side with secondary open, using a variable-voltage, variable-frequency source. Loss is 1050 W at 230 V, 50 Hz and 500 W at 138 V, 30 Hz. Find hysteresis and eddy-current losses respectively at 230 V, 50 Hz.

  1. 508 W and 542 W
  2. 468 W and 582 W
  3. 498 W and 552 W
  4. 488 W and 562 W

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Correct answer: (A) 508 W and 542 W

Explanation

Both tests have identical V/f:230/50=138/30, so peak flux is unchanged. Hysteresis loss scales as f, while eddy loss scales as f². Let H+E=1050at50Hz; at30Hz,0.6H+0.36E=500. Solving gives H=508.333Wand E=541.667W, matching **508Wand542W,A**.