Conditions to be Satisfied for Parallel Operation of Transformers

• When the load current increases above the capacity of one transformer, we can connect one more in parallel instead of replacing the existing transformer with a bigger one.
• Following are some of the reasons for connecting the transformers in parallel :

       1. Higher reliability.
       2. Better maintenance and repairs.
       3. It is easy to make addition in the existing setup.

• If a single large transformer is used then its failure will shut off the installation. The parallel transformers solve this problem and improve the reliability.
• It is possible to repair or maintain the transformers in parallel connection one by one without shutting off the plant.
• With increase in the load current we can easily add a new transformer to the existing parallel unit.

Conditions to be Satisfied for Parallel Operation of Transformers.
Q. What is the need of parallel operation of transformers? Discuss the conditions to be satisfied before connecting two 1-phase transformer in parallel.
Q. Discuss the conditions of parallel operation of synchronous generator.

• The following conditions are required to be satisfied in order to ensure successful parallel operations :

1. The transformers should be connected taking their polarity into consideration such that the net voltage around the loop is zero. If the polarities go wrong then there will be a short circuit.
2. The voltage ratio of the transformers should be the same. This will avoid the no load circulating current.
3. The per unit impedances of the parallelled transformers should be approximately equal. The currents delivered by the two transformers are proportional to their ratings if their per unit impedances are equal. The ratio of equivalent leakage reactance to equivalent resistance should be same for all the transformers. If they are unequal, then the transformers will operate with different power factors.