Because of the critter guard on this bushing we can not determine if the heating is from a bad lead connection or perhaps an internal lead issue, any ideas?

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Ramona Baldyga, PE
Senior Substation Maintenance Engineer
Alliant Energy

Ramona,

 I would suggest you narrow the span a bit more and then raise the level until you find the point with the greatest signal (and, emissivity being equal, temperature). My bet is you'll find it at the base of the bushing a pretty clear indicator of an internal fault.

What does your dissolved gas analysis show? 

One other thought: can you lift the critter guard with a hotstick and improve the view? 

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Thermally Yours,

John
ASNT NDT Level III #48166
The Snell Group
www.thesnellgroup.com
www.thermalsolutions.org
800-636-9820

Ramona,

This situation could be serious.  You could have a bushing failure if the bushing is failing or you could have an outage (best case) if the lead burns off.  I would do whatever it takes to move or remove the critter guard so you can get an unobstructed image. I would even insist on an outage to remove the critter guard if it could not be lifted out of the way.  You could also look for elevated levels of hydrogen, methane, ethane or ethylene in the transformer oil.  If you can, testing the transformer's headspace gas for combustible gases may give you an idea if its an internal bushing problem.

 

Scott