Flashover at 35kV!

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Mark Rowley
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Flashover at 35kV!

Post by Mark Rowley »

So the other day I was very gently testing the 60kv prcipitator supply between 25kV and 30kV. Neutron count was roughly at 200cpm with the corona tube so I decided to slowly ramp it up to 35kV. Suddenly a continuous flashover erupted on the BeO feedthru (pictured). In error, I had previously thought they were rated for closer to 60kV, but I was wrong. After digging through a ton of archival posts I learned it was actually rated for around 30kV. Well, 30kV won’t suffice for my goals so I recalled Carl Willis’ “Oil Socket” which not only used the same BeO insulator, but allowed him to flirt with 90kV potentials. Not that I’d ever go 90kV (or even 60Kv) but it would make for a stable arrangement for 50kV with a robust safety margin.

The other pics are of Carl’s completed socket, my BeO feedthru on my system, and my newly purchased parts for the oil socket. To make this work I’ll be repositioning the fusor so the feedthru is facing downward and the viewport facing up. I’ll post some pics of the arrangement as it starts taking form.

As a side note, I can’t say enough good things about the treasure trove of information contained in the archives. While searching for the “oil socket” I ran across about 20 other unrelated posts of interest (all subsequently bookmarked).

Mark Rowley
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Mark Rowley
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Re: Flashover at 35kV!

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Richard Hull
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Re: Flashover at 35kV!

Post by Richard Hull »

My BeO insulator will withstand 42kv easily when setup as shown in the image below.
I fashioned a 1/4 thick HDPE disk of two machined semicircles held together with two nylon screws threaded into the HDPE notches as seen in the image.
I place a wad of silicone HV putty at the top of the metal skirt on the base of the insulator. As the collar plate of HDPE is tightened just above this skirt top, the putty oozes out. This forces an arc to go around the collar. I put a zip lock baggie over the entire insulator to keep dust and grime off the porcelain and its HDPE collar.

I still wipe down the insultaor with a soft cloth soaked in everclear ethanol and dry it prior to major runs.

Richard Hull
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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Richard Hull
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Re: Flashover at 35kV!

Post by Richard Hull »

These BeO insulators have no voltage rating that I have ever seen. They are federal stock numbered and are U.S. naval, bulkhead, antenna insulators. Designed to take damaging salt sprays, resist corrosion and pass a connection from the antenna out of a ship's radio room to the outside "long wire", longwave antenna.

They obviously, in the right hands, can make a superlative fusor HV insulator when used in a dry laboratory environment. The voltage handling capability is limited by the users ability to work up additional externally applied safe guards. Field control applied by adroit and learned hands is the easiest to apply. Oil bath systems are much more tricky. Both will work.

I have applied, in extreme moments, 45kv without arc over using this insulator on fusor IV. I will soon have to add a small toroid for the ultimate field control to the top of the insulator. The toroids are regularly sold by John Freau every year at the HEAS fleamarket. They are used by Tesla coilers to avoid their 9 foot arcs from jumping the 3 feet to the grounded primary turns or the coil form itself. This is field control at work.

This insulator should ideally have a 3-5 inch diameter toroid placed on the top HV terminal, carefully and thoughtfully placed for broad range field control.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Mark Rowley
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Re: Flashover at 35kV!

Post by Mark Rowley »

Current progress with the HV handling upgrade involved rotating the fusor so the insulator was facing down. This would allow a relatively easy design facsimile of Carl’s oil socket. However, that meant the viewport would be facing the ceiling. So I built an acrylic frame to support the camera and a cylindrical lead shield to slide over the viewport (not pictured...still under construction). In the side of the lead cylinder will be an opening with an angled mirror for the video camera to see the plasma. The lead cylinder will be capped with lead to limit xrays and backscatter.

Replicating Carl’s design was fairly straightforward and I am looking forward to testing it with the 60kV precipitator supply in the next day or two.

Richard, I like the field control arrangement and no doubt I will take your advice and learn more about it. You mentioned oil baths are “more tricky”. What kind of things should I be looking out for? I’ll also dig around and try to find some literature on the subject. Same with field control dynamics.

I haven’t searched the forums much for field control threads but I intend to do so soon. Have there been members here who have employed this method? I’ve seen a few pictures of people bending copper tubing into a circle and putting that on the terminal, but not much else.

The two pics show the upgraded fusor arrangement up top and the oil socket with a fresh charge of oil.

Mark Rowley
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Re: Flashover at 35kV!

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Good work there Mark. Many ways to skin a cat. The tricky part of any oil arrangement is leaks. Oils of various types and glues of many types are not long-term friendly. Keep an eye on the oil and its seal against gravity and possible defeat of a glued or epoxy seal.

We are in luck field control wise. Static field control (DC) is easy to setup and as long as grime, dust, dirt and moisture are fully controlled, you are OK.

RF field control is a lot more tricky. Fortunately we do not involve ourselves with high RF potentials in the fusor world. I learned a lot about RF field control back in the 11 years of Tesla coiling up to 16kw input energies.

Check out "Nemesis"! (image) This is how you keep 15 foot arcs off a high voltage terminal from hitting a grounded ring of copper pipe 4 feet away. The image shows not how to prevent arcing, but how to control it and direct it away from nearby ground points (field control).

You will notice one strike on the protective ground guard ring around the primary coil. this is not a straight line arc as the field control forced it not to jump directly to the guard but follow a much longer "field line" bowed outward. The arc took a curved outward arcing path towards the camera to come back and hit the ground ring. The insulator was air in this case. Notice not one hit on the coil winding, itself. (field control).....Without the top toroidal field control terminal, the coil would have flashed straight down to ground, destroying it with the full multi-kilowatt arc energy.

Richard Hull
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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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