Response to 'Freak Failure Mode of Transformer.

I must thank Mr. Partha Chattopadhyay, Chief Engineering of Tata Metaliks, Goa plant for his kind comments in the form of an email in response to my earlier blog on ‘Freak Failure Mode of Transformer’. I value his comments since it comes from a fine electrical engineer know of. He brings in his original perspective on the issue? But I have a more important reason for putting it up in my blog since I have grown up as an engineer to believe that any engineer can learn more through such interactions of live case studies and increase his/her width and depth of knowledge which would ultimately benefit our society in many ways.

However, as desired by him, I assure him that I shall try to put in my thoughts on the issue of fire and explosion of transformers more cogently in my next blog entry in greater depth and try my best to explain the physics of this phenomenon. Fire and explosion of transformer is a serious issue which is often neglected or not properly understood even by experts on safety. However, once understood properly, plant engineers can take care of this serious issue during the procurement stage and during operation and running of the plant. It is also important since it affects so many people and society at large. And it might be of interest not only to electrical engineers but also safety engineers, project managers and other plant engineers too.

Signing off for now

Dibyendu De

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Dear Mr. De,

I have following points for your consideration:

1) Transformer oil’s flash point is around 140deg Centigrade. High Dielectric strength only ensures that no spark occurs (which means breaking of insulation and passage of huge current, which may lead to attainment of flash point) between to points having high voltage gradient. Transformer oil having good dielectric strength will catch fire easily provided it attains its flash point.

2) Also, DGA helps us in finding incipient fault of transformer winding. Generally, cotton and cellulose materials are used for transformer winding. Traces (ng/L)of Methane, Ethane like gasses can be detected in the transformer oil. Such traces can not contribute further to transformer oil’s natural inflammability.

I guess that a huge spark might have occurred when the hawk touched with the terminals of the transformer. Such short circuit will certainly generate massive electromagnetic force, which can cause mechanical damage to the insulators, resulting into leakage of the transformer oil. In addition, I feel there was an accumulation of transformer oil on the top cover of the transformer due to some unattended leakage. Probably this accumulated oil caught fire first and then the leakage contributed to continuation of fire.

Following measures may act as antidotes to this type of trouble

1) we must not neglect small issues like checking of all safety devices 2) periodic oil testing, 3) keeping the transformer free from leakages, 4) periodic checking of transformer’s protective devices, 5) Use of fire retardant synthetic oil(Very expensive!!).

Yes we need to institutionalize maintenance audit. This will certainly help us in finding systemic gaps.

Looking forward your reply,

With regards,

Partha Chattopadhyay

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Dibyendu De