How will a transformer fail anyway? I don't know, but would assume that it would be the wire burning in half and/or shorting out due to over-amping. SMF

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Faillures in dry transformers:

Insulation breakdown: Primary to secondary windings, this is one of the main reasons that the sec. winding needs to be earthed at a low voltage TX. to avoid getting a higher mains voltage on the sec. (safe) side.

Shorted turns: Depending on how well the windings touch each other eg. low resistance contact between turns means that the secondary becomes a single turn transformer and the winding will burn out very quickly and a lot of damage will be done to the remainder of the windings and a rewind or write off is necessary.

Winding open circuit: Could be at a tapping or shorted turn gone o.c.


Faillures in oil filled distribution transformers.

Same as for dry TX's and a few more below

In oil filled TX's there are acidity levels in old oil , ingress of moisture, deteriation of paper insulation to name a few.

In New Zealand we usually take oil samples twice a year from substation TX's to determine the condition of the oil and TX.
Carbonlevels indicate some form of arcing at the windings or terminations. Acidity can cause leakage current to earth. lots of varnish can block radiator pipes and reduce circulation hence overheating etc.

I draw a line here now because I think the subject pertains more to dry TX's.

Merry X mas and a great 2006. Raymond

The product of rotation, excitation and flux produces electricty.