Explosion of 138kV transformer in Madison Substation

[RRaghunath]

The grid transformer exploded on 19th Jul'19 at Madison substation belonging to American Transmission Company. I understand the cause is failure of Load Tap changer in the transformer.
Load Tap Changer failures are rare to my understanding. I am used to MR, Germany make On Load tap changers (OLTCs) which seem to be highly reliable.
Appreciate if some one could enlighten me on what was wrong with the OLTC in case of Madison 138kV transformer.
Thanks

 

[RRaghunath]

I am curious to know is it related to contact wear and tear of OLTC or is it to do with driving mechanism?

 

[JAE]

Is this what you are posting about:

https://wkow.com/news/top-stories/2...ame-for-madison-substation-fire-company-says/

 

[oldrunner]

Was there information concerning how old the transformer was? Transformers have problems with the degradation of the paper and solid insulation. Actually the life of a transformer is the life of the insulation. Usually the transformer is withdrawn from service but if there have been a lot of shocks or even years of vibrations, the transformer can fail prematurely. Very difficult if not impossible to predict the actual failure time. From a structural standpoint, it appears the complete isolation of the coils has to be accomplished to eliminate the vibrations and shocks. (This doesn't address faults) This is an issue with IEEE 693 which doesn't mention (can't find yet) of insulation degradation.

 

[RRaghunath]

Thanks JAE for the news item. I haven't seen this earlier but the content is same what I have seen - "a component inside the Blount Street substation’s transformer failed" and it is 'voltage regulator' or OLTC.
I presume it is the worn out contacts of OLTC that caused the problem, any idea!!

 

[dauwerda]

Usually the transformer is withdrawn from service but if there have been a lot of shocks or even years of vibrations, the transformer can fail prematurely.

I know in the US some utilities like to let transformers remain in service until they fail. That way the replacement is a capital cost (paid for by rate payers) as opposed to an o&m cost which would cut into profits of the utility.