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#19168 - 12/21/02 08:18 AM Transformer Fire??  
Joe Tedesco  Offline
Joined: Oct 2000
Posts: 2,749
Boston, Massachusetts USA
Transformer fire

Any idea why a 15 year old 75 kva single phase oil immersed pole mounted distribution transformer would suddenly blow a hole through the bottom of the tank, pop its lid and spew flaming oil out onto the surrounding area? Examination after the fact indicated a turn to turn short in the secondary windings. But why?



[This message has been edited by Joe Tedesco (edited 12-27-2002).]

Joe Tedesco, NEC Consultant

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#19169 - 12/21/02 10:11 PM Re: Transformer Fire??  
Ron  Offline
Joined: Mar 2002
Posts: 582
White Plains, NY
The winding fault and resulting catastrophic failure is from conductor insulation failure. The insulation failure could be from a continuous overvoltage condition, overload or manufacturer assembly failure. Most likely an overload. This transformer was probably serving 3-5 residences and as typical for a utility transformer, it is easier for them to replace it after failure, as opposed to monitor loads and apply it correctly to the loads or application.
Consider that the full load current of the transformer secondary is 312.5A @ 240V, and many new utility services are 240V and 200A plus.
Interesting question from an attorney.

[This message has been edited by Ron (edited 12-21-2002).]


#19170 - 12/27/02 01:34 AM Re: Transformer Fire??  
Bjarney  Offline
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
It may be wise to avoid NEC 450 numbers with respect to a utility-owned transformer. Design and application of these devices is based on significantly different standards.

Litigation based on applying the NEC to poletop oil-insulated transformers would likely be unsuccessful.

#19171 - 12/27/02 01:12 PM Re: Transformer Fire??  
Joe Tedesco  Offline
Joined: Oct 2000
Posts: 2,749
Boston, Massachusetts USA
I never realized that this question was from a lawyer! I should have been more careful. In the meantime the lawyer should not have asked a legal question of me and should have hired a consultant!

Bill please lock this message out.

Joe Tedesco, NEC Consultant

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