10/10/2026
Why Are Transformers Operated in Parallel?
Definition: Transformers are operated in parallel when two or more transformers are connected to the same primary supply and their secondary terminals are connected to a common busbar to supply the load together.
6 Main Reasons for Parallel Operation.
1. Increased Load Capacity.
* When the load increases, another transformer can be connected in parallel.
* The total power capacity increases.
2. Improved Reliability.
* If one transformer fails, the other transformer can continue supplying part of the load.
* This helps reduce power interruptions.
3. Maintenance Without Complete Shutdown.
* One transformer can be switched off for maintenance while the other continues supplying essential loads, provided it has sufficient capacity.
4. Better Efficiency.
* Transformers can be switched ON or OFF according to the load demand.
* This can improve overall operating efficiency.
5. Future Load Expansion.
* Additional transformers can be installed when the plant's power demand increases.
6. Easy Load Sharing.
Conditions Required for Parallel Operation.
Before connecting transformers in parallel, the following conditions must be satisfied:
1. Same voltage ratio — to avoid circulating currents.
2. Same polarity — to prevent short circuits.
3. Same phase sequence — for three-phase transformers.
4. Same phase displacement — the vector groups must be compatible.
5. Similar percentage impedance — for proper load sharing.
6. Compatible impedance angles — to help ensure appropriate load sharing.
