Step 1: Transformer parallel operation basics.
When transformers work in parallel, their voltage ratios, phase sequence, and impedances determine how they share load. Step 2: Load sharing criteria.
If physical impedances are equal but transformer capacities are different, load sharing will not be proportional.
To ensure proportional load sharing:
- Per-unit (pu) impedance should be equal (based on kVA rating).
- X/R ratio (reactance to resistance) should also match to maintain correct power factor sharing. Step 3: Why both?
Equal pu impedance → proportional sharing.
Equal X/R → same power factor, avoids circulating currents. Conclusion: Both per-unit impedance and X/R ratio must match.