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Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
In cool, or cold, weather, coconut oil is a solid. That might make life interesting for you if you are using it as an insulator as the impurities will concentrate between the crystals as it freezes, potentially giving rise to easy breakdown.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Bored Chemist wrote ...
In cool, or cold, weather, coconut oil is a solid. That might make life interesting for you if you are using it as an insulator as the impurities will concentrate between the crystals as it freezes, potentially giving rise to easy breakdown.
Yes.
A lot of the impurities can be removed by distillation, I think (some details in a paper lined to above) but it reduces the volume considerably. (actually I seem to remember something in the paper about decanting while cooling, and leaving the solid residue behind, I'll need to read it again to refresh my memory)
In any 'real' 4HV scenario it will probably be pretty hot, though (certainly well above the 23C or whatever melting point)
This 'may' involve warming the whole thing prior to use in cold weather, no big deal really, especially if you want it circulating for cooling anyway.
Hoping to make some more progress on this, and other projects, soon, I'm a bit distracted by other 'chores' at the moment.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
There is another consideration for transformer oils that may be discussed in the Chemistry forum. If they are subject to a rapid change of temperature, as can be the case in a high energy arc, will they decompose explosively?
Years ago, there was a paper by IEEE examining the use of certain insulation in metal-clad switchgear, that had suffered damage while clearing a fault. The damage was in excess of what the fault energy could have done. Tests revealed that the phase arc barriers, made of a combustible material, with good strength and insulating properties, had simply detonated. It was intended to replace asbestos which was too heavy and fragile.
I have a copy of a report about damage in the factory I worked at, which had had this happen, and the conclusion was boiled down to relating the forces to several sticks of dynamite.
The down side of this ,was the use of fibreglass phase barriers. Once an operator decided to put a turbo generator on line despite heavy 'dew' everywhere. The switch blew up, and the burning fibreglass incinerated the breaker, wiring and instruments on the door. The operator wasn't hurt. They never stand near a breaker. They have the control room close it by remote control. It took our crew about 30 hours to fix the mess.
With the experimental crowd out there finding finding increasingly higher voltage and current transformers to work with, substitute oils may have hidden hazards.
In a a large transformer, whenever an arc occurs under under oil the sensitive protection takes it off line, and in some units, a pop-up flag shows there was a transient over-pressure caused by the gasses produced.
Registered Member #1521
Joined: Thu Jun 05 2008, 10:46AM
Location: Hungary
Posts: 128
I experimented with a lot of oils. The most worse was the transformer oil. Without any dirt, or water, it's actually pretty good (200kV/cm dielectric strenght in a range of a few cm spark gap). But the most tinies dirt in it, or even 6ppm water can totally destroy its dielectric strenght, we measured 180kV/cm for example, then I just touched the surface of the oil, and it went down to 10kV/cm.... I'm using now only silicone oil, it is chemically very resistant, has a high boiling point, can be bought with almost any kind of viscosity, (from water like to complete jelly like behavior) and it doesn't really cares about any small dirt, or water in it (actually silicone is water resistant). We measured 60kV/cm with silicone oil. Its dielectric constant at 100Hz is around 2,8, plus it has a very low dissipation factor at 100Hz. The only problem is with this is its price.
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Coconut oil as a dielectric (better than transformer oil)
