Why Do We Use Rated KVA Values in Transformer Impedance Calculations?

[ranju]

For the transformers in parallel.. there's a relation
Z1/Z2 = S2 (rated)/S1(rated)
where Z1 & Z2 are the impedences while S1 & S2 are KVA ratings of the two transformers.
Now why we are taking rated KVA values..??
I mean if Z1/Z2 < S2(rated) / S1(rated)... we increase S1 to satisfy the relation but we are already taking the rated value..so we can't increase it...! Maybe I am going wrong..
please correct if I am mistaken..basically I want to understand the relation practically...!

 

[Achy47]

Hello,

Thank you for your question and interest in understanding the relation between transformers in parallel. The equation you mentioned, Z1/Z2 = S2 (rated)/S1(rated), is known as the impedance ratio and it is used to determine the proper loading of transformers in a parallel configuration.

To answer your question about why we use the rated KVA values, it is because the rated KVA values represent the maximum capacity of the transformer. The transformer should not be loaded beyond its rated KVA value as it could lead to overheating and other issues. Therefore, when determining the proper loading of transformers in parallel, we use the rated KVA values to ensure that the transformers are not overloaded.

Now, in the case where Z1/Z2 < S2(rated) / S1(rated), it means that the impedance of one transformer is lower than the other, which could result in one transformer carrying more load than the other. In this case, the transformer with the lower impedance would need to be loaded with a lower KVA value to balance the load between the two transformers. This is why we use the rated KVA values to ensure that the transformers are not overloaded.

I hope this explanation helps to clarify the relation between transformers in parallel. If you have any further questions, please let me know. Thank you.