Thanks for your help.Transformer Ratings: Questions & Answers

[Lunat1c]

Hi,

I have a couple questions regarding transformers:

1. When you're told that a particular transformer is rated at 2000kVA, is that referring to the output or to the input rating of the TX? Or is it correct to say that the apparent power on both windings will be equal to that?

I view the 2000kVA as the maximum loading of the transformer (even though it can be overloaded a bit with the correct setup) however with this in mind I'm having doubts whether I can use S=VI on any of the two windings.

2. If you have a 2000kVA three-phase 30000/6000V transformer connected as delta-star, then is the apparent power per phase equal to 2000kVA or is that the total?

 

[zgozvrm]

Seeing how this post is a couple of months old and no one has replied, I'll assume that the OP has either given up, or found the answer to his questions.

In the interest of answering these questions for those interested, I have decided to post my answers even though this is a homework forum.


1. The kVA rating of a transformer refers to both the primary (input) and secondary (output) side of the transformer. Remember, power in equals power out. Of course, there is a bit of loss due to heat, but for the sake of calculations, a "perfect" transformer is considered (that is, one that loses no power to heat).

2. The power per phase of a three phase transformer is one-third the overall power rating of the transformer (whether delta- or wye-connected). So, there would be approximately 667 kVA per phase.



For more information, see: http://ecmweb.com/mag/electric_understanding_basics_wye/