winding resistance tester and CPC 100

[moon1958moon]

Hi, everyone. I used a winding resistance tester to test 0.75 MVA transformer primary (13800-600). I got a unbalance phase resistance. H1-H2 WAS 2.6om AND H1-H3 WAS 3.8OM. H2-H3 WAS 8.7OM.

I DON'T THINK SOMETHING WRONG WITH THE TX, IT IS ACCEPTANCE TEST. I USED CPC-100 TO TEST TX AGAIN. I GOT EVERY PHASE WERE AROUND 2.6OM.

I THINK THE REASON FOR WINDING RESISTANCE IS THAT I DID NOT DISCHARGE THE TX AFTER H1-H2 TESTING AND STARTED TO TEST H1-H3 IMMEDIATELY. BUT THE CPC-100 DISCHARGE THE TX AUTOMATICALLY.

JUST REMIND TO DISCHARGE THE TX AFTER TEST.

[SecondGen]

hmm...this is an interesting scenario, it almost seems like you had two or more wingdings in series by accident? I don't see how discharging the transformer would have made that big of a difference. How long did you apply current before taking your readings? I would be interested to know more about which test set you were using and how you had the leads connected.

[moon1958moon]

First, used the AEMC 6240 10A Micro-Ohmmeter. It need five minutes to get stable.

Then use omicron CPC 100. pretty quick to get stable. and CPC automatically discharage the TX. The TX is wye to Delta. I tested the high sigh. impossible to series two winding.

[SecondGen]

The fact that you were using a 10A ductor is probably why your readings were funky. Was it battery powered? If the batteries were low you wont get accurate readings because the current is not stable, especially if you are pushing current for 5 minutes. Using a test set that operates off of utility supplied AC like the Omicron CPC 100 is a much better method. Putting two windings in series was a long shot, I know, I was just brainstorming.

First, used the AEMC 6240 10A Micro-Ohmmeter.
It need five minutes to get stable.
Then use omicron CPC 100. pretty quick to get stable. and CPC automatically discharage the TX. The TX is wye to Delta. I tested the high sigh. impossible to series two winding.

[moon1958moon]

Thanks ,buddy
it is battery powered. you are right.I will try it next time.

[stevenwerynski]

i am young in the testing world but just seen something similar the other day. the senior guys on site came up with that it is possible to have two wingdings in series with certain type of xfmr. they concluded to remove the jumpers that tie the wingdings together which i believe stabilized the results. Just a thought good luck

[Biscuit]

This happened to me once. I accidentally put two wingdings in series and my reading doubled.

it is possible to have two wingdings in series with certain type of xfmr.

[lester mcmanaway]

I use the cpc regularly and the only time I've seen issues like this it's either due to incorrect connection ( 2 windings like previously stated) or just a high resistance at your lead connection point. What current did you test at with which leads?

[HalinMD]

First, used the AEMC 6240 10A Micro-Ohmmeter. It need five minutes to get stable.

Then use omicron CPC 100. pretty quick to get stable. and CPC automatically discharage the TX. The TX is wye to Delta. I tested the high sigh. impossible to series two winding.

If you were testing a wye-delta xfmr then you should have been testing HI/HO, H2/HO and H3/HO.