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John

Sat Apr 08 2006, 05:14PM

Registered Member #327 Joined: Sat Mar 18 2006, 07:47PM
Location: Belgium
Posts: 6

What insulation distance has to be taken into account when placing HV components in High voltage oil ?
I plan to put a voltage multiplier in oil

ragnar

Sat Apr 08 2006, 05:22PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

I good place to start is to be pessimistic and pretend it's in open air. 1kV/mm.

But you can probably work with 1/3 to 1/5 the tolerance - so perhaps 5kV/mm. Be generous =)

Marko

Sat Apr 08 2006, 05:29PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Mineral oil has usual strength of 5kV/mm, it can vary but just keep it safe and make spacings large enough so no breakout can occur in any conditions.

Tesladownunder

Mon Apr 17 2006, 03:34PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Proper transformer oil has a much higher dielectric strength of 60kV in a standardised setup. There are standards for this eg ASTM D1816 (Google for that) which set out the electrode shape and distances, voltage rise times etc. It is actualy quite hard to fing the exact details of distance that this refers to but there are many other oil properties that affect spark breakdown in oil.

Peter

Steve Maurer

Tue Apr 18 2006, 05:14AM

Registered Member #133 Joined: Fri Feb 10 2006, 10:27PM
Location: Pensacola, Florida
Posts: 47

If you intend to use mineral oil, then the following would apply (interpreted from: Handbook of Electrical and Electronic Insulating Materials, 2nd edition by W. Tiller Shugg):

Type I and Type II mineral oils (ASTM D3487) have a minimum dielectric breakdown of 28 kV @ 60 Hz across a 1-mm gap with VDE 0370 electrodes (radius of 1 cm?).

These same mineral oils have a minimum impulse dielectric breakdown of 145 kV across a 25.4-mm gap between a needle (negative) and a sphere (grounded). [This equates to an impulse dielectric breakdown of 5.7 kV per mm.]

Keep in mind that the dielectric breakdown voltage will vary with: (1) electrode shape, material, surface condition, and area, (2) the spacing between the electrodes, (3) the length of time of electrical stress, (4) temperature, (5) purity of the oil, and (6) concentration of dissolved gases.

Based on the impulse dielectric breakdown strength, I would maintain less than 5 kV per mm (in fairly pure mineral oil with low moisture levels). Avoiding any sharp metal points in the construction will also definitely help (reduces electrical stress on the surfaces).

John

Thu Jul 27 2006, 07:04PM

Registered Member #327 Joined: Sat Mar 18 2006, 07:47PM
Location: Belgium
Posts: 6

I put a dummy load in an aquarium filled with HV oil. I installed this aquarium in a box with water. I can put 15 Kv onto this dummy load. However i see that when I put a grounding wire into the water there is an arc flashing over. What can be the reason for this ? the electric field , is the water acting as a capacitor ?

Steve Conner

Fri Jul 28 2006, 11:44AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Oil behaves differently to air. You can't really use a kV/mm figure because it depends greatly on the electrode shapes, far more so than in air. But as a very rough rule I think you can have things 6 times closer together as long as they're not pointy. Go and look up the shape of those "VDE 0370 Electrodes" if you want a better feel for things. :P

John

Wed Aug 02 2006, 06:57PM

Registered Member #327 Joined: Sat Mar 18 2006, 07:47PM
Location: Belgium
Posts: 6

Is it more reliable to put everything in epoxy ?

dan

Wed Aug 02 2006, 07:30PM

Registered Member #223 Joined: Mon Feb 20 2006, 06:42PM
Location: Ottawa, Ontario, Canada
Posts: 125

Well if you blow a component it's actually possible to replace it if it's only under oil. Also Oil can transfer heat far better then epoxy. Which is usually not a problem with multipliers. With epoxy if you blow something you got to throw the whole thing out. Epoxy does have a much higher breakdown voltage though. Which option is the best is up to you. It all depends on what youâ€™re trying to accomplish. But ideally you would use air as you insulation and just keep connections free of sharp edges and as far apart as possible. Also air isn't messy and it's easy to perform maintenance on whatever device your trying to insulate. I would only use oil or epoxy if I really needed to.

But what I cant figure out it why you have two aquariums one filled with oil beging submere into another filled with water

Where exactly is it flashing over? In the oil or to the water filled box?

John

Wed Aug 02 2006, 07:44PM

Registered Member #327 Joined: Sat Mar 18 2006, 07:47PM
Location: Belgium
Posts: 6

Dan ,
thanks for the reply.
I put 100 resistors in the aquarium with HV oil for use as dummy load.
In order to keep this cool, I put this aquarium in a box with water, in which I can circulate the water.
When I put a grounding wire in the water, the first moment there is a arc. It looks like the water is also at a High voltage, however there is no direct contact between the HV components and the water. Even there is glass in between ?

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