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so the question i have is what about BOD, Bio-Oxygen Demand, is this a big deal, if its so much higher than PCB, silicone, hydrocarbon oils? or does it not matter for 1-2 years. (maybe the power company worries about 20-45 year life cycles)
my devices only need to last 1-2 years, so i see the table on page 4 of 8, the only significant difference between organinc oils and others is the high (250ppm) BOD/BOC measurement. Also, for background, i boil my oil and vacuum degas it ,then pump in into my metallic transformer cases, which are almost air-tight.
removeing water vapour and dissolved gasses almost doubles the dielectric strength. 40kv/mm is typicall, though i design for 10-20kv/mm Max.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Hiya Patrick
I've been interested in environmentally-friendly vegetable dielectric oils for a few years now, and have always promoted their use in this forum.
My understanding is that maize oil ("corn oil") is one of the least suitable, because of its age-related viscosity and oxidation profile. See:
2009 J. Phys.: Conf. Ser. 183 012014 Selection of a suitable vegetable oil for high voltage insulation applications I L Hosier*, A Guushaa, A S Vaughan and S G Swingler ECS, University of Southampton, Highfield, Southampton, SO17 1BJ, UK
and you can read the full text for free here:
"Corn oil" has also been targeted by false food label racketeers in the past - in the UK, at least - so take care that what you buy is actually what it says it is on the label:
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Patrick wrote ...
crap on a stick!
i guess sunflower oil is better.
what do you use proud mary?
I've actually been using sunflower seed oil, without probs, though that paper puts sunflower seed oil as joint worst together with corn oil.
Yellow olive oil - favoured by the paper - is the cheapest sort of olive oil in UK supermarkets, so I might give it a go next time.
The patent literature has all sorts of vegetable dielectric cocktail recipes, a jigger of sunflower, so many percent of palm, a dash of carnauba, and so on, but that's always the way with patents. They couldn't patent yellow olive oil alone, could they?
My guess is that the food grade oils sold in supermarkets are quite pure (except the green ones containing chlorophyll etc) and low in water, to improve their long term shelf life in plastic bottles, and make them as bacteria-unfriendly as possible, a matter of importance in salad oils which will not be heated before they are eaten.
Several other 4HV members have used vegetable oils in C&W columns with good effect, and it's almost always the people who've never used them, and don't read recent scientific literature, who object to them most.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
really, ? sunflower and corn the worst? it looked to me that sunflowerwas the best, i was looking at canola oil, but i thought the hell with it i will just use Envirotemp FR3 fluid. I will buy 5 gals this summer, from cooper power systems, because im a student they may sell it to me cheap, i hope. (i need 2.2 gallons for my transformer.)
Proud mary since you are such an advocate for biologic oils, could you make a list like the source you quoted, of most to least suitable, based on only expense, oxidation, age loss factors, (not viscosity).
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Patrick wrote ...
really, ? sunflower and corn the worst? it looked to me that sunflowerwas the best, i was looking at canola oil, but i thought the hell with it i will just use Envirotemp FR3 fluid. I will buy 5 gals this summer, from cooper power systems, because im a student they may sell it to me cheap, i hope. (i need 2.2 gallons for my transformer.)
Proud mary since you are such an advocate for biologic oils, could you make a list like the source you quoted, of most to least suitable, based on only expense, oxidation, age loss factors, (not viscosity).
and you are right, they modify the content of the oils, becuase they wont be allowed to patent a common product, already in existence.
In the paper to which I gave you a link above, the conclusion reached is - wakey wakey! - 4. Conclusions
"A wide range of vegetable oils were aged, characterised and then ranked according to their ability to withstand thermal ageing in air. Under this scheme, yellow olive oil appears to be the best food grade oil for inclusion into high voltage plant, offering the best resistance to ageing and the lowest dielectric loss. Over most of the indicators of ageing it performed at least as well as the model Envirotemp oil. Rapeseed oil offers “intermediate†properties and so may find use in some applications, especially if improved through the use of an antioxidant. Oils to avoid are corn oil and sunflower oil, this is mainly due to their tendency to oxidize much more than the other oils and to thicken on ageing."
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Patrick wrote ...
lol ! yeah thats what i think!
what about peanut oil, is that good?
This one has useful-looking graphs comparing the dielectric constants of a range of food oils - including peanut oil - at radio frequencies -
ON THE USE OF DIELECTRIC SPECTROSCOPY FOR QUALITY CONTROL OF VEGETABLE OILS A. Cataldo, E. Piuzzi, G. Cannazza1, E. De Benedetto, L. Tarricone XIX IMEKO World Congress Fundamental and Applied Metrology September 6−11, 2009, Lisbon, Portugal
This one has lots of comparative data on breakdown voltage at 50-60Hz, and variation of dielectric constant with temperature, which will affect electric field distribution inside transformers:
Essam A. Al-Ammar Evaluation of Seed Oils Based on Statistical Breakdown Data for their Application as Insulating Fluids in Distribution Transformers European Journal of Scientific Research Vol.40 No.1 (2010), pp.15 -26
The main thing I've learned from browsing the literature over the last decade, is that few of the papers agree with each on which vegetable dielectric coolant oil is best.
Replacing the world's existing ~40 billion litres of mineral transformer oil with vegetable oil is big business, so research sponsored by Canola Corporation discovers that canola is best, while Gambino and Gotti researchers find that olive oil is da best if you know whats-a good for you, and so on.
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About Bio-Oils for HFHV Transformers.
