On Wed, 10 Sep 2003 15:45:23 +0100 someone who may be Pyromancer
wrote this:-

http://news.bbc.co.uk/1/hi/england/london/3096098.stm

Seems to have changed now, but earlier versions of that piece had a
picture of the burnt out wreck of what looked like a very large
transformer with a couple of dodgy-looking air-con cooling units bolted
on to it.

Was that in any way connected with the fault, or just a random pic of
wrecked HV gear?

Yes and no.

Transformers used in high voltage systems are generally cooled with
oil. PCBs were tried, but didn't last long after the first explosion
spread PCBs around the surrounding buildings. Air cooled
transformers are expensive. The oil is cooled by convection in the
"radiators" attached to the transformer, which usually have a large
fan attached to them which is brought into play at times of heavy
demand, doubling the capacity of the transformer. On smaller
transformers the oil is cooled by the pipes that stick out from the
transformer.

Oil deteriorates over time for various reasons and as it does so it
gives off gas. The Buchholz alarm that caused the control room to
start the switching sequence is there to detect problems with the
oil. In some circumstances where there is an imminent danger of
explosion it will automatically disconnect the transformer, in less
serious circumstances it will issue a warning to the control room,
which can then disconnect the transformer in a controlled manner.

These alarms are not always able to detect problems with the oil
fast enough. In that case the transformer will probably explode,
with burning oil being thrown out. The picture in the report, which
I expect the BBC used, is of a transformer that has suffered this
fate. So the picture is not of what happened, but of what they were
taking steps to avoid happening.


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David Hansen, Edinburgh | PGP email preferred-key number F566DA0E
I will always explain revoked keys, unless the UK government
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