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

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.