Transformers

Explanation of question 7

In Fig. 11.1, the load on the primary is

  1. 2.4VA
  2. 48VA
  3. 96VA
  4. 960VA

The answer is :- 2 

Transformer turns ratio is 20:1, therefore the secondary voltage will be 240/20 = 12V. By Ohm's law, I = V/R = 12/3 = 4A. Load on the transformer (power) = V x I = 4 x 12 = 48W or 48VA. It is common to specify transformer load in VA rather than the more conventional unit, watts.

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