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

A. Transformers will be overheated
B. Power factors of both the transformers will be same
C. Parallel operation will be not possible
D. Parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load

Answer: D

Explanation:

If the percentage impedances of the two transformers which are working in parallel are different, then the parallel operation is still possible, but load sharing will not be in the ratio of their kVA loads.

Condition 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 an Unequal impedance ratio but the same KVA.

Unequal Impedance ratio but same KVA:

• Mostly this parameter is used to enhance plant power capacity by connecting existing transformers in parallel that have the same kVA rating, but with different percent impedances.
• This is common when budget constraints limit the purchase of a new transformer with the same parameters. It is important to understand that the current divides in inverse proportions to the impedances and a larger current flows through the smaller impedance.
• Thus, the lower percent impedance transformer can be overloaded when subjected to heavy loading while the other higher percent impedance transformer will be lightly loaded.
• Thus, the power factors at which the two transformers operate will be different from the power factor of the common load.