Dry transformer problem

[KnicksJets]

Folks
We suspect some problem with our dry transformer 6.9 KV to 480 Volts step down.
We did phase to ground megger testing and didn't find any problem. What other test do you suggest to conform the transformer is working fine? We are going to recommend an impedance check of the primary delta winding to see if it is balanced.
Anything else?

 

[Skogsgurra]

What seems to be the problem with your transformer? Insulation test and impedance measurements reveal so different failures that I cannot figure out what the reason for the tests is.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[isquaredr]

I once had a faulty 11/.415kv Dy11 transformer with healthy megger & continuity readings. The fault was on the lv side c-n, direct short. I discovered the fault by energising via a variac connected on the lv side each phase to neutral in turn. Just be careful of those HV connections whilst doing so.

 

[Zogzog]

What IR values did you get? What test voltages were used? WHat was the DAR/PI results?

You should also do a TTR and check the bolted connections.

What type of problems are you seeing?