Paralleling Transformers

[katag]

Just wondering if anyone can clear up some stuff about paralleling transformers. I was working on Complex Imaginary Exam 1 Question 62. The question gives you a total load current and the impedances of 2 paralleled transformers and then asks to solve for one of the transformers contribution to the total load current. In the solutions they solve using

I1 = Z2/(Z1+Z2) * I-load

This seems pretty straightforward and they do not specify the MVA rating on the transformers so I guess you must assume that the impedance values are on the same base and you can just add them without changing any bases. My problem is that when I first worked this problem I used an equation provided in the Chelapati book which states that "The current through each transformer in a transformer paralleling configuration are as follows:

I1 = Zeq/Z1 * I-load

I2 = Zeq/Z2 * I-load

And I got an incorrect answer

It seems like the equation from the test solution and these Chelapati equations contradict each other. Am I missing something?

TIA

 

[mhelms_2]

It appears they used the current divider formula.

 

[cconnawa]

Just wondering if anyone can clear up some stuff about paralleling transformers. I was working on Complex Imaginary Exam 1 Question 62. The question gives you a total load current and the impedances of 2 paralleled transformers and then asks to solve for one of the transformers contribution to the total load current. In the solutions they solve using

I1 = Z2/(Z1+Z2) * I-load

This seems pretty straightforward and they do not specify the MVA rating on the transformers so I guess you must assume that the impedance values are on the same base and you can just add them without changing any bases. My problem is that when I first worked this problem I used an equation provided in the Chelapati book which states that "The current through each transformer in a transformer paralleling configuration are as follows:

I1 = Zeq/Z1 * I-load

I2 = Zeq/Z2 * I-load

And I got an incorrect answer

It seems like the equation from the test solution and these Chelapati equations contradict each other. Am I missing something?

TIA

I1 = Zeq/Z1 * I-load is exactly equal to I1 = Z2/(Z1+Z2) * I-load because in Chelapati's formula, Zeq equals the equivalent Z of the two transformers in parallel. I.E., Zeq = Z1*Z2/(Z1+Z2) If you divide Zeq/Z1 based on that definition, you get Z2/(Z1+Z2).

So how did you get a wrong answer? You must not have calculated Zeq correctly. See if that works, and then repost what you discover. Thanks.

 

[katag]

You are correct! I calculated Zeq wrong and it all makes sense now. Thanks so much!