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Arc over problems and coupling recommendation on 10kW SRSGTC...?

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Anon01

Wed Oct 20 2010, 02:01AM

Registered Member #1589 Joined: Sun Jul 13 2008, 06:40PM
Location:
Posts: 70

I'm having some weird acrover problems from about the 1/4 from the bottom of the sec to the primary. Correct me if I am wrong, but could a combo of coupling and improper grounding cause this? I'm thinking of how much to take off my pri and I just can't think of where to start. Here is the only pic of it I have of it where one is able to view the pri and sec with any significant detail. Take note that I've shortened the sec in the pic to make the bottom of the sec level with the primary for an even tighter coupling. What should I do? Halloween is coming close and I'm wanting to fix this.

Sec: 36"x8.25" 24AWG
Primary: 1/2" ID (5/8"OD) copper pipe with 1/2" spacing
Power supply: 14.4kV 15kva distribution transformer ballasted to 50A at max power
Capacitors: CDE 942 series, I forget how many uF since I designed and built this coil 2 years ago, but near .1uF@18kV(Going to be upping it to 24kV soon to accommodate 120BPS operation without a problem)
Spark Gap: 1800RPM synch motor with variable phase driver, 14" tip to tip rotor, currently operating at 480BPS
Toroid: 6"x20"(I think) Alu ducting on bottom, larger alu foil covered inner tube on top, I forget sizes.

Okay-ish time lapse shot here.

What should I do? It has caused a small of damage to the sec and I do not want to wind another. I want to figure it out because I am wanting to go from 4J per shot at 480BPS to 20J per shot at 120BPS and that should increase the output voltage considerably, which increases the chance of arc over and ultimately crippling damage. Thanks in advance!

teravolt

Wed Oct 20 2010, 03:48AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

hello Anon01, nice coil have you tried puting a projection sticking out past the toride?

When I went to the first to links in your thread my norton lit up saying it is blocking trogens. maby your host that has your pictures is infected. don't know

monokel

Wed Oct 20 2010, 03:30PM

Registered Member #2981 Joined: Thu Jul 08 2010, 01:47PM
Location: Germany
Posts: 35

Hello Anon01, nice coil.
Maybe the problem is that the coil is much above ground. Maybe some more "lightning conductors" will help.

Do you use inductive ballast ? If so, I believe that with 120 BPS it will difficult to obtain both a good power factor and a good power throughput and to prevent very big voltages and currents due to resonance effects.
E.g. with your 14.4 kV transformer you can obtain an apparent power of 15 kVA and a power throughput of 12.8 kWatts with a ballast inductance of 94.5 H and a cap with 0.1 ÂµF. The firing angle must be -67 degrees. But the cap will charge up to 46 kV in this configuration. If the firing angle changes the voltage of the cap can increase dramatically, e.g. with a firing angle of 0 degrees the cap will charge up to 119 kV (hope you have a static safety SG; probably the iron core of the transformer will get saturated and this will also prevent so big voltages).

There are other configurations with 120 BPS, e.g. with a ballast inductance of 22.5 H, a cap with 0.1 ÂµF and a firing angle of -142 degrees you obtain an apparent power of 15 kV, a real power of 13.5 kWatts. But in this configuration the cap is also charged up to 47 kV. If you don't want so big capacitor voltages the power factor will be worse (assuming that the capacitance is 0.1 ÂµF; with a higher capacitance the cap voltage can be decreased while getting a good power factor).

Regards, monokel

HV Enthusiast

Wed Oct 20 2010, 06:43PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Arcing at the base of the secondary to primary is very indicative of poor (or non-existant) grounding. Remember, that with proper grounding, the base of the secondary should be at earth ground.

I would first try improving the ground connection.

Anon01

Wed Oct 20 2010, 06:47PM

Registered Member #1589 Joined: Sun Jul 13 2008, 06:40PM
Location:
Posts: 70

Teravolt, thanks for the compliment. Yeah, it actually started doing this about 2 halloweens ago with a fluorescent bulb sticking out to the sides on top of it.

You know, I had someone else just tell me that. I'll take a look and see what's going on with that host. Thanks for informing me.

Monokel: Thanks. Could you explain what you mean by "is much above ground"? I've never really thought of that to ever be a problem. I have a decent ground when compared to something like what a DRSSTC should have. It is 3 14AWG wires heading to a 1.5' square grid with 5 1' long stakes in the ground. I'm going to be beefing this up for this Halloween's performance though. 4 4AWG wires to 4 2' long solid copper rods spaced about 4' apart.

Yes, I use essentially a pile of mots to ballast it to where I want it. It turns out that I only have 25A@240V to play with this year, so I will be wanting to find a nice sweet spot. Do the tank voltages really get and remain that high? I do have a safety gap set at 17kV but I've never had it fire off even with my projected capacitor voltage has been considerably more than that. I think the xfmr core saturating has dampened the spiking effect considerably... I also do not have the money to buy such larger capacitor banks at that rating unfortunately. :\

Thanks for your input!

teravolt

Wed Oct 20 2010, 07:42PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

have you tried puting a rod off the top for a projection like a DRSSTC. from the picture that youv'e shown it looked like the spark from the top is wraping around to the base. Am I missing something hear? maby if the srike rail was a little higher it would help. Are you getting inter winding arcing

Anon01

Wed Oct 20 2010, 08:34PM

Registered Member #1589 Joined: Sun Jul 13 2008, 06:40PM
Location:
Posts: 70

I have tried putting a nail on it but it severely decreases the arc length. It makes sense that it does too. The voltage does not have to build up as much before breaking out, etc etc.

It didn't happen very much, but it arcs from about the 1/4 from the bottom of the sec to the center of the primary. It isn't a super high current arc either, and did not seriously damage the winding, but it did burn a tiny bit of the enamel/poly coating. Since then I have ran over the areas(there are about 5-6) with about 20 more coats of poly.

EVR: That's it? It's only my ground?

Coronafix

Wed Oct 20 2010, 10:08PM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

If it has damaged the secondary then you may just get further problems there. If it is not too bad, I would clean it up and spend a couple of week adding coat upon coat of varnish, this will not only make it look absolutely fabulous but will increase it's coupling handling ability.
The other thing you can do is decrease the coupling by raising the secondary. i have found that a fairly loose coupling is needed when pumping a lot of power into a coil, regardless of size.
Also what Dan said about good grounding is crutial. The bigger the arcs coming out the top, the bigger the grounding cable required, not to mention the actual ground rod. Tesla spent most of the money on the Wardenclyffe tower on his grounding system.

teravolt

Thu Oct 21 2010, 03:28AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

do you think that your primary is arcing to your secondary and does it arc in the same spot?

monokel

Thu Oct 21 2010, 05:08PM

Registered Member #2981 Joined: Thu Jul 08 2010, 01:47PM
Location: Germany
Posts: 35

Anon01 wrote ...

Monokel: Thanks. Could you explain what you mean by "is much above ground"? I've never really thought of that to ever be a problem.

I mean that it may be a problem if the distance between the lower end of the coil and the ground is not small compared to the hight of the coil. I can't proof this; it's just an assumption. The topload and the ground are like the two plates of a plate capacitor. The primary coil is on or next to a line connecting these two "plates" and thus streamers can go into the primary. Of course, may people build their coils in this way.

Anon01 wrote ...

Do the tank voltages really get and remain that high? I do have a safety gap set at 17kV but I've never had it fire off even with my projected capacitor voltage has been considerably more than that. I think the xfmr core saturating has dampened the spiking effect considerably...

Of course these calculations are based on the assumption that the ballast is an ideal inductance and the transformer is also ideal (no saturation). In this case there would be large voltages and currents (in the case of 60 HZ resonance the voltages and currents would theoretically get infinite). As you already said, saturation effects will probably damp these resonance effects. Maybe this is associated with losses and worse power factors.

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