There are several reasons for operating transformers in parallel. Some of these reasons are:
- When the load of a transformer on a transmission line system exceeds the designed capacity of the transformer, one method to solve this problem is to replace it by a transformer of a larger capacity. but the cost of such changes will be greater than if the original transformer is paralleled with another to carry a portion of the load.
- When the amount of power transformed is greater than can be transformed by using a single transformer, it is necessary to use two or more transformers in parallel.
- Spare transformer units are required to ensure continuity of service in case of damage and hence it is desirable to supply the load through two or more transformers and thereby reduce the size of spare parts. This procedure may reduce the total installed capacity.
Parallel Operation At no Load:
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| Transformers connected in parallel. |
The Transformer primaries are connected in parallel across the line of distribution system and the secondaries are paralleled too. The figure above shows the parallel connection of transformers. Primary voltages across the two transformers are equal since both of them are from the same source. Ea and Eb are the induced voltages across the two transformers at no load. If the turns ratio are not equal, then Ea is not equal to Eb.
Transformer A will supply a reactive load to the secondary of Transformer B and the primary of Transformer B will feed this load back to the primary circuit. This will cause a reduction in voltage at the secondary of Transformer A and a rise in voltage on the secondary of transformer B. The Terminal voltage on the secondaries after paralleling is common to both transformers and is the voltage V2
