transformer no load losses, and preferred method to test it?

[fastline]

We are examining a couple 400kva 480pri/208/120sec transformers that are quite old and I suspect drinking up energy with no load losses.

Curious what you guys usually see as reasonable loss for modern transformers? I have not checked one in a long time because they always have loads but if memory serves, I think about 1% of the KVA rating?

in any case, I have tested these in two ways. Either use my meters to determine PF, then calc the amps and volts, or use the 3P KW feature on my meter which is assessing all 3 legs, current on one, and PF.

 

[steve66]

If they are really old, even if they are operating as designed, a new transformer will be compliant with the newer DOE requirements, and will be much more efficient.

New ones will also be larger, so hopefully there is plenty of space around these.

 

[fastline]

Thank you, but I need to "quantify" the changes with the higher brass. I want to test no load power consumption and determine what new ones will be. That is the only way they will justify an upgrade.

 

[electrofelon]

You will probably find DOE2016 transformers to be around .3% . In this thread post #11, I measured some transformers of varying age with two different meters:

Please discuss transformer losses vs %Z

I know what transformer impedance is and how it is calculated. It is, of course, a somewhat unique use of the word "impedance" How does %Z relate to load and no load losses? I suspect there are other factors at play where we could have transformer A that has a lower %Z yet higher no load losses...

forums.mikeholt.com

 

[steve66]

Here are some numbers for SQD.

https://www.productinfo.schneider-e...4.xml/$/NewEnergyEfficientThreePhase-70EBBC64

I think you should be able to measure and calculate the efficiency on the existing transformers using either method you mentioned. I would do both, and compare the numbers you get.

I would also suggest measuring the voltage and phase angle on every phase, just to make sure one phase doesn't have an issue.

 

[jim dungar]

Please consider the loading profile of your transformer. Decades ago the DOE efficiency standards were setup for small to men medium size general purpose dry type transformers typically used in offices and schools where they spent most of their life lightly loaded. The standards at this time required the top efficiency at roughly 35% loading. This was typically accomplished by lowering the no load core losses, with a slight negative side effect of occasionally increasing the full load losses.