If the percentage impedances of the two transformers working in parallel are different then

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ESE Electrical 2014 Paper 2: Official Paper
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  1. Transformers will be overheated
  2. Power factors of both the transformers will be same
  3. Parallel operation will not be possible
  4. Parallel operation will still be possible

Answer (Detailed Solution Below)

Option 4 : Parallel operation will still be possible
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Detailed Solution

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Conditions for parallel operation of transformer:

  • Same voltage ratio or same turn ratio.
  • Same phase angle shift
  • Same frequency rating of both the transformer.
  • The same polarity of the transformers.
  • Both should be connected in the same phase sequence.

 

If the percentage impedances of the two parallel-connected transformers are different then also the parallel operation is possible.

This is the case of unequal impedances ratio but the same kVA.

Unequal Impedances ratio but same kVA:

  • This is commonly used when there are budget constraints.
  • In this current divides in inverse proportions to the impedances and larger current flows through the smaller impedance.
  • The lower percent impedance transformer can be overloaded when subjected to heavy loading while the other higher percent impedance transformer will be lightly loaded.
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