Somewhat OT - Transformer oil

Tim Leech · 2004-09-22T09:25:49+00:00

I picked up an Oxford oil-filled welding set the other day, a biggersize (250A) than I've been using for years. It was cheap, no warrantyetc.There were a couple of broken feed-through terminals in the top, so Ihad to lift it out of its tank to sort them & check the general stateof things.These sets generally accumulate some water at the bottom of the tankafter some years of work. Even if they aren't left out in the rain(I've been guilty of that one), then 'breathing' as the set cyclesthrough warm & cold will draw in fresh air to the dop, which will thendump its moisture within the tank.This one was different from others that I've cleaned out in that allthe horizontal surfaces were covered with a greeny-brown sludge,apparently dumped there by convection currents within the oil. I'veseen brown sludge, to a lesser degree, but the green tinge suggests'copper' to me.So far as I can tell so far the windings on the transformer & reactorare fine, but I don't intend testing it under load until it's back inits tank of oil.One suggestion is that the oil may be acidic & has dissolved somecopper. Any other ideas?My plan was to put 25l of fresh transformer oil in (which is costingme more than buying the set :-( ) and top up from the top of what'sbeen removed after it's had a few days to settle out, but I'm nowwondering whether it may have been topped up with an unsuitable oil atsome time. It holds around 40 litres, I'm not keen to buy another 25if I don't have to.CheersTim

Sep 22, 2004 24 Replies

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Peter Scales 21 years ago

I did do a bit of research into this when I realised that I needed to top up my old BOC Oxford set. I discovered that the machines were originally filled with 'Diala B' from Shell and this is a high dielectric strength low vapour pressure mineral oil - the spec sheet is available on the net if you want to Google for it (545 hits for 'Diala

+B oil' (no quotes)). As far as I can tell it has never been anywhere near a polychlorinated bi-phenyl. Why anyone would ever want to tip nasty crud like that into a poor harmless little Oxford set is beyond me.

I was offered some Diala B by a Birmingham based welding supplies outfit. Morris Lubricants of Shrewsbury said "Diala B? Oh, yes, that'd be our Transformer Oil...", available in 25-litre drums at a price.

The primary purpose of the oil in an Oxford set is to cool the set, not to insulate it, so the high dielectric strength of Diala B is just a bonus as far as I can see. You could probably fill it with chip fat without adverse effects if you felt that way inclined.

Safe? Well, I doubt I'd want to drink any, but I'd be happy to get my spanner out of the bottom of the welder by hand if I had to, if I turned it off first.

TTFN

Pete

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Tim Leech 21 years ago

I don't think anyone here has ever suggested that they've done so, or have I missed something?

Cheers Tim

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Peter A Forbes 21 years ago

Just to add what Peter Scales has already said, the Shell Diala oil conforms to BS148 which covers mineral insulating oils.

There are no PCB's (PolyChlorinated Biphenyls) in this oil, and PCB production was halted in 1970 by all accounts:-

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PCB's were made for high-voltage insulation purposes, and as far as I can see they were never used in low-voltage equipment. Most of this stuff was taken out in the 1970's, certainly by the early 1980's you couldn't lay your hands on anything near to it.

If anyone has anything else in the way of info I'd like to see it, just to add to the knowledge base.

Peter

-- Peter & Rita Forbes Email Address: snipped-for-privacy@easynet.co.uk Web Pages for Engine Preservation:

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Arthur G 21 years ago

Back in the salad days of my youth, I worked for a high voltage capacitor maker, and we used Diala B for impregnation of the lower spec capacitors. I can categorically state that having spent six years working with the stuff, Diala is NOT PCB, nor does it contain any PCB and never did. It is a common or garden mineral oil.

The most widely used PCB that I'm aware of in the capacitor field (used until early 70s) had the trade name Araclor. If you're offered a barrel of this, politely decline.

Regards, Arthur G

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