Paralleled Transformers: Why Overload & How to Prevent It?

[Nahian]

When transformers with the same turns ratio, but different kVA ratings are paralleled , it is possible for the smaller transformer to be overloaded and the larger transformer to be lightly loaded.Why is it so? Can anyone please show mathematical and theoretical explanation?And what can be done to stop the overloading of the transformer?

 

[anorlunda]

The impedances will be different. Therefore, the sharing of power and current between the parallel branches will not necessarily be in proportion to their KVA ratings.

If you can't do the calculations by hand, any load-flow program modeling those transformers in parallel will calculate the splits in current and power.

 

[Nahian]

Thanks

 

[Svein]

When transformers with the same turns ratio, but different kVA ratings are paralleled

Then you are creating a loop - through transformer A and back through transformer B. Be very careful!