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Coconut oil as a dielectric (better than transformer oil)

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Ash Small

Sat Aug 08 2015, 10:15PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I wasn't sure whether to post this in HV or here, so, if in doubt.....

I read sometime ago that coconut oil was a better dielectric than transformer oil in an MOD paper.

Today my 'better half' showed me a 'product' she'd bought in Tesco's for Â£4.99 (she thinks) which the label claims to be 'Extra Virgin 100% Raw Cold Pressed Coconut Oil' (ingredients: organic extra virgin coconut oil).

It contains 250ml. I plan to try it for insulation at some point. I should probably boil it for a while first.

Apparently, coconut oil has a dielectric constant of 2.9 where as transformer oil has a dielectric constant of 2.1:

klugesmith

Sun Aug 09 2015, 04:38AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Maybe it's time for you to make a dielectric oil breakdown-test cell and get out a NST. Some oil testing standards call for a stirrer.

1439095008 2099 FT172537 Automatic Oil Bdv Test Set

Conundrum

Sun Aug 09 2015, 06:48AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

Yeah, try it and post your results.
Baby oil is rumored to also work if purified and dried under a moderate vacuum.

Mads Barnkob

Mon Aug 10 2015, 12:57PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

There is properly some other properties with transformer oil like notasflameable as insert_generic_oil_name or the willnotoutgassomethinghighlyexplosive_factor is different.

I can confirm that baby oil is excellent for a back rub.

2Spoons

Tue Aug 18 2015, 12:18AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

Here's a paper worth looking at. Looks like drying the oil is very important. You might also consider castor oil, though that is more appropriate for capacitors, having a dielectric constant of about 4.7 and a dielectric strength of about 65kV/mm.
]coconut_oil_eru_2001.pdf[/file]

Ash Small

Sat Aug 29 2015, 10:57PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

klugesmith wrote ...

Maybe it's time for you to make a dielectric oil breakdown-test cell and get out a NST. Some oil testing standards call for a stirrer.

Sorry I've not responded sooner, I've been away camping in the nether regions of North Cornwall, somewhere between Morwenstow (GCHQ Bude) and Tintagel. Mobile internet connections don't seem to have arrived in that part of the world yet

That's an excellent idea Rich. I was planning on building a test rig for 'hand rolled' capacitors so adding a bit of extra functionality can only be a bonus. I already bought these to use as a safety gap for the capacitor tester:-

Thanks for the interesting link, 2Spoons.

klugesmith

Tue Sept 01 2015, 10:49PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Looks good, Ash. How was the weather on your camping trip?

I, too, have bought cabinet knobs for this purpose. Maybe it's time to start a thread about oil testers instead of oils. I wonder how special an oil needs to be, to withstand prolonged application of 15 kV RMS from a NST across a 1 mm gap?

What follows, except for the final paragraph and image, went up on another forum a couple weeks ago.

For numerical results to correlate with other labs and product data, it would be good to mimic the popular standards ASTM D1816 and IEC 60156. At least where it's easy and inexpensive.
Here are one summary of those standards,

, and one commercial tester UI image:

The Internet teaches that both standards include polished electrodes with 25 mm radius of curvature. Gap widths are 1 mm, 2 mm, and 2.54 mm. When oil stirring is called for, the impeller shall have standard dimensions and turn at 200 - 300 RPM. One standard also allows a magnetic stirring bar at the bottom of the oil cup.

Are any readers here in a position to access either of the actual standard documents, and answer a few questions about details? Legitimate copies cost about $40 to download. That helps to fund development, maintenance, and distribution of standards. I found some free sources that require registration and/or installing a special reader, and probably also install unwanted junkware and startware or worse.

The smallest model boat propeller available at one hobby shop is about 20 mm wide and has the right number of blades. Neither its package, nor its maker's website, give any specs except a list of the RC boats that it fits. After fruitless Internet searches, physical measurement and test fitting taught me that the nyloc nut has a 1-72 right-hand thread.

This morning, following Ash's lead, I actually put some parts together for fun. Started with disposable plastic tongs for serving salad. They better be oil-resistant!

Let's make some sparks under oil. Automatic spark detection and shutdown of the HV can wait.

Ash Small

Wed Sept 02 2015, 10:11AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

We had every type of weather you can imagine except snow, I think, we certainly got our money's worth

We even had the air sea rescue helicopter plucking surfers from the rocks and returning them to tne beach, but due to a 'fake' 128Gb micro SD card I bought the week before only actually having 8Gb of memory, I've 'lost' all the photo's I took. (Moral: Don't buy cheap SD cards from Ebay).

Anyway, back to the topic in question, I've also been giving this some thought. I want a test rig to test capacitors and dielectrics, and also to test various types of DC flyback based circuits. I'm guessing I'll need some sort of HV resistive divider in order to measure the voltages using standard meters, 'scopes, etc.

My initial plan was to construct something out of wood and copper tubing along the lines of classic 'museum' pieces however plastics are cheap and easy to use. I like your 'salad tongs' idea, but you still need to connect the wires to the cabinet knobs, and I'm still considering alternatives.

I want to get the design right before I build it so it's as versatile as possible. Can I add any additional functionality? I certainly want to include provision for a second 'safety gap' if required, for example.

The voltage divider also requires some thought, especially integrating it into the setup in the most convenient manner. (1,000:1 or 10,000:1, for example?....I want to measure to a theoretical 50kV, so want to design for at least twice that. 100kV sounds like a good start for design purposes))

Maybe I should just change the title of this thread, and maybe edit it so that it can be transferred to the 'projects' section at a later date?

EDIT: Found this on Wikipedia:-

Transformer oil testing procedure

To assess the insulating property of dielectric transformer oil, a sample of the transformer oil is taken and its breakdown voltage is measured.
The transformer oil is filled in the vessel of the testing device. Two standard-compliant test electrodes with a typical clearance of 2.5 mm are surrounded by the dielectric oil.
A test voltage is applied to the electrodes and is continuously increased up to the breakdown voltage with a constant, standard-compliant slew rate of e.g. 2 kV/s.
At a certain voltage level breakdown occurs in an electric arc, leading to a collapse of the test voltage.
An instant after ignition of the arc, the test voltage is switched off automatically by the testing device. Ultra fast switch off is highly desirable, as the carbonisation due to the electric arc must be limited to keep the additional pollution as low as possible.
The transformer oil testing device measures and reports the root mean square value of the breakdown voltage.
After the transformer oil test is completed, the insulation oil is stirred automatically and the test sequence is performed repeatedly. (Typically 5 Repetitions, depending on the standard)
As a result the breakdown voltage is calculated as mean value of the individual measurements.

Conclusion: The lower the resulting breakdown voltage, the poorer the quality of the transformer oil!"

I also read that the standard radius of the electrodes should be 25mm. (~2" Dia)

Ash Small

Fri Sept 04 2015, 03:16PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I've given this a bit more thought, and found a local supplier of 8mm (5/16th") copper tubing, which I currently plan to use. I can paint it with polyurethane enamel and bake it on to provide some extra resistance to corona, and, if necessary, add more insulation easily if required.

I also want to design in a method of shorting the electrodes with a 'crowbar' on a chicken stick, which will be retained in place by neodymium magnets.

I've also designed a 'hinged shelf' to support the flask containing the oil to be tested.

I've a few ideas regarding gap adjustment. I'm still thinking through the alternatives, but plan to draw something soon

Signification

Sun Sept 06 2015, 06:21AM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

@kludge;
I have really been wanting to build some of these things. Including the oil-based tester--thanks for the standards. The prop reminds me of what I consider to be the most unusual patents of Nikola Tesla. He describes a water fountain powered by an AC motor generating resonant whirlpool section-overflows of water. Finally, he illuminates the water with a radioactive substance!

Fast forward to 'today': underwater pumps and ultra-bright rainbow LED's that can fill sections of swirling laminar texture water with Arduino controlled LED- flow which burst out into colors when the laminar surface breaks!

If you are familiar with Tesla's patents, they, as a rule, relate to HF AC and resonance apps. The title of this patent "Fountain" no. 1,113,716 10/13/1914.

I have the bulk of this built (1999), the only problem--the trolling prop won't quite reach the inner edges of the giant PVC wall--critical for thrust!

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