dry type 2500 kVA transformer varnish melting

[OmgVlt]

One of our transformers began to exhibit excessive vibrating and noise. We shut it down, and this is what we found (see photos). Has anyone ever experienced this before and what could be the cause?

 

[OmgVlt]

Another photo of the varnish melthing

 

[ScottyUK]

Is that core bolt supposed to be isolated from the core? It looks as though it should be. Has the insulation failed?

Can you safely arrange a thermographic survey while it is energised, bearing in mind the hazards you will be exposed to during the survey?

 

[pwrengrds]

Megger the core at 500 vdc. It should have only one grounding point which is typically at the top of transformer. Multiple grounding points could cause core heating. (that seems like a lot though).

Are the core bolts all tight?

Is the load excessive (what % of load was it at) or unbalanced? (is it possible that the TX is single phased?)

David

 

[ghostbuster7]

Similar--- 2 mva. tx. core overheated and varnish/paint bled onto all the core laminations
Problem: transformer exposed to incoming single phase fault situation for 91 minutes before H.V. breaker tripped

 

[rcw retired EE]

What is/was the operating voltage? Over excitation might cause core overheating.

 

[Skogsgurra]

What does this transformer supply? Is it a standard mixture of loads or is this transformer doing just one thing? Like supplying a process line, a single VFD or what?

In some cases, a VFD can initiate and maintain high frequency ringing on the primary side and that leads to an overheated core. One "unhappy" combination is when the primary is fed from a cable grid and supplies an CSI inverter. The steps associated with the CSI switching then initiates ringing in the primary with several kHz and quite high amplitudes. That heats the core a lot.

Has this transformer been running for years with the same load? Or is it a new installation? Has anything been changed lately? More load? Changes on the primary side? Is the transformer from a reputable manufacturer? Or is it one of those Gonella transformers that used to "Darwin eliminate" themselves from the surface of the Earth?

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[waross]

Is this a three legged core?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[OmgVlt]

Transformer is a 13.2kv to 480v SqrD, 3 phase transformer. We found deterioration of insulation in the coils and core. This is at one of my remote locations, therefore I'm waiting on the meter history to determine the load at the time. This transformer supplies power to a standard mixture of loads and that have been in place for years without any changes to it. On the primary side, the utility company has recently relocated there feeders onto new poles, but the conductors are original. It is possible that the transformer could have been single phasing, or that the load is unbalanced, because the melted varnish is more concentrated on the left coil..?