isolation xfmr

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ron

ron

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New York, 40.7514,-73.9925
When specifying a step down transformer for high harmonic loads, I spec a "K" rating number, electrostatic shield, copper windings, yadda, yadda.
Why does it seem that an isolation transformer, does not have a "K" rating?
 
Re: isolation xfmr

Ron, good question. Why would anybody install a isolation transformer without a "K" rating? There are few good reasons to provide an isolation for sensitive equipment.

1. Establish a new ground reference point near the point of use.

2. Dissipate the heat generated by harmonics.

3. Common mode noise rejection.

4. Isolate harmonics.

The only reasons I can think of to supply an isolation transformer without a "K" rating is voltage control and voltage drop on linear loads.
 
Re: isolation xfmr

The isolation transformer secondary windings will see harmonics in the same way that a step down transformer secondary wining would see it.
I spoke to a Square D Rep, and he said it was a low volume item (isolation xfmr), and they don't want to have too many versions of something that sits around. He said with a 4 week lead time, they will build one with a k13 rating.
 
Re: isolation xfmr

majorpower.com has a section of Iso X-formers with different K-ratings available. The chart indicates the recommended K-rating for the percentage of non-linear load. K-13 and higher seam to be good for 75% or more non-linear. The price difference for higher or lower K is in the low hundreds of $$$. The higher the rating the better??
 
Re: isolation xfmr

Would it make sense to consider extra derating for the Isolation Transformer or going to a larger KVA size? I though that might be more cost effective than a special order and might help with lead time issues. Unless it creates other issues.
 
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