Fire risk in electrical oil filled substations

[kurnal]

Oil filled substations often use "non combustible" oil for cooling and insulation purposes. I understand that internal arcing can still cause the breakdown of this oil to produce explosive gases eg hydrogen and acetylene. (she was only the welders daughter but she had acetylene legs)(sorry)

The oil is regularly tested for water contamination and special gas detecting relays can be provided to detect the buildup of gases and cut the power. Even so I have seen the aftermath of a number of serious fires and explosions in transformers over the years.

So I was wondering whether the oil really is non combustible, or whether it could be ignited by an explosion of a small volume of gas? Heres an example of one such fireball I found whilst browsing ( link to 5Mb mpeg)

http://205.243.100.155/frames/mpg/XfrmBlast1.mpg

[John Webb]

Kurnal,

Are we perhaps looking at the difficulty of igniting oil in bulk and the ease of igniting the same material in a finely divided form, ie a spray well mixed with air? I assume that a plain leak probably will result in a pool of liquid within a bund with little problem. But a major failure within the transformer - perhaps caused by overvoltage, short-circuit or lightening strike - could result in a explosive disruption of the transformer containment and the formation of such a spray.
There used to be the Electrical Research Assc. at Leatherhead that dealt with national grid problems; if they are still about they may have some information on this problem.