HV coupling caps: Good for anything?
J. Aaron Holmes, Tue Aug 22 2006, 03:23AMMy local utility recently declared their willingness to part with a number of coupling caps. They're oil-filled porcelain-body caps of the sort usually used to couple transmission lines to small PTs. They're 16" in diameter and about 4' tall, weighing about 400lbs, and are rated at .22uF at 170kV! A friend of mine said he took one of these apart one time and that it was filled with hundreds of little green doorknob caps in strings--basically a gigantic MMC
Of course, they're not meant for pulse discharge. Not, at least, at their rated voltage. Any thoughts as to their fitness for a particular HV sport? I don't have a part number, unfortunately (trying to get that now).Regards,
Aaron, N7OE
Re: HV coupling caps: Good for anything?
Avalanche, Tue Aug 22 2006, 03:42AM
IIRC, there are two grades of ceramic caps, 1 type being more suited to pulse discharge use than the other. I tried some ceramic caps in a mini SGTC recently, and they died a few minutes later, they're too lossy :p
I guess you could use them in a (huge!) marx gen, or for smoothing the supply from a flyback for a large lifter or something... but i'm sure someone will come up with a better idea
Avalanche, Tue Aug 22 2006, 03:42AM
IIRC, there are two grades of ceramic caps, 1 type being more suited to pulse discharge use than the other. I tried some ceramic caps in a mini SGTC recently, and they died a few minutes later, they're too lossy :p
I guess you could use them in a (huge!) marx gen, or for smoothing the supply from a flyback for a large lifter or something... but i'm sure someone will come up with a better idea
Re: HV coupling caps: Good for anything?
Hazmatt_(The Underdog), Tue Aug 22 2006, 08:18AM
I would probably use them as dividers for Tesla Coil measurements. Now I say that knowing that their intended frequency is 40-400 Hz. What I would do is run a frequency sweep in simulation to give me a derating characteristic curve, and possibly build a 30kv inverter and do a live sweep of the capacitor to find out its characteristics. Then determine the correction factor, and use it as the divider.
Hazmatt_(The Underdog), Tue Aug 22 2006, 08:18AM
I would probably use them as dividers for Tesla Coil measurements. Now I say that knowing that their intended frequency is 40-400 Hz. What I would do is run a frequency sweep in simulation to give me a derating characteristic curve, and possibly build a 30kv inverter and do a live sweep of the capacitor to find out its characteristics. Then determine the correction factor, and use it as the divider.
Re: HV coupling caps: Good for anything?
Sulaiman, Tue Aug 22 2006, 08:54AM
Ceramic capacitors come in grades,
e.g.
CLASS/Tempco/D.F.PERCENT@1MHz
1/NP0/ 0.1
1/N750/0.1
1/N2200/0.2
1/N3200/0.2
1/N5250/ 0.3
2/X5T/1.5
2/X5V/1.5
N750 MEANS -750 PPM/DEGREE CELCIUS etc.
d.c. smoothing, and disk capacitors are usually classII
which is what I'd expect a hv line frequency capacitor to be.
I've used classII ceramic capacitors for a sgtc
they aren't very good,
but suitably (?) derated will survive ok.
(monitor for overheating)
Sulaiman, Tue Aug 22 2006, 08:54AM
Ceramic capacitors come in grades,
e.g.
CLASS/Tempco/D.F.PERCENT@1MHz
1/NP0/ 0.1
1/N750/0.1
1/N2200/0.2
1/N3200/0.2
1/N5250/ 0.3
2/X5T/1.5
2/X5V/1.5
N750 MEANS -750 PPM/DEGREE CELCIUS etc.
d.c. smoothing, and disk capacitors are usually classII
which is what I'd expect a hv line frequency capacitor to be.
I've used classII ceramic capacitors for a sgtc
they aren't very good,
but suitably (?) derated will survive ok.
(monitor for overheating)
Re: HV coupling caps: Good for anything?
Steve Conner, Tue Aug 22 2006, 09:45AM
I think those might be used as capacitive dividers, in which case the caps have to be precision. So they would have to be one of the better grades of ceramic (as the poor grades all have lousy tolerances and tempco's) and hence I think they might do well in RF and pulse operation. Even poor capacitors seem to work OK in Marx banks, anyway.
If it were me, I think I'd try and build it into a Marx bank inside the original body. Or make the porcelain body into a big oil filled Tesla resonator and use the guts I removed as the tank cap for it.
Or if you can get four, you could make a colossal 1600lb 4 stage Marx out of them
Steve Conner, Tue Aug 22 2006, 09:45AM
I think those might be used as capacitive dividers, in which case the caps have to be precision. So they would have to be one of the better grades of ceramic (as the poor grades all have lousy tolerances and tempco's) and hence I think they might do well in RF and pulse operation. Even poor capacitors seem to work OK in Marx banks, anyway.
If it were me, I think I'd try and build it into a Marx bank inside the original body. Or make the porcelain body into a big oil filled Tesla resonator and use the guts I removed as the tank cap for it.
Or if you can get four, you could make a colossal 1600lb 4 stage Marx out of them
Re: HV coupling caps: Good for anything?
J. Aaron Holmes, Tue Aug 22 2006, 03:41PM
I'll get more info and maybe post a pic. Something tells me that I won't be able to afford *four* of them! Maybe I should see if they'll keep the porcelain and let me take the guts? The porcelain is awfully cool looking, though!
BTW, I said "coupling", but really meant what Steve pointed out, which is that these are for voltage dividing and measurement. I suspect just about everybody here has seen what I'm talking about; they're in almost every substation.
I like the idea about building a Marx or something else *inside* the porcelain tank. Hmmm...
Regards,
Aaron, N7OE
J. Aaron Holmes, Tue Aug 22 2006, 03:41PM
I'll get more info and maybe post a pic. Something tells me that I won't be able to afford *four* of them!
Maybe I should see if they'll keep the porcelain and let me take the guts? The porcelain is awfully cool looking, though!BTW, I said "coupling", but really meant what Steve pointed out, which is that these are for voltage dividing and measurement. I suspect just about everybody here has seen what I'm talking about; they're in almost every substation.
I like the idea about building a Marx or something else *inside* the porcelain tank. Hmmm...
Regards,
Aaron, N7OE
Re: HV coupling caps: Good for anything?
Hazmatt_(The Underdog), Tue Aug 22 2006, 11:31PM
I still think using them as dividers and contributing data from a carefully controlled experiment would be worth much more to the forum then another Marx generator.
Hazmatt_(The Underdog), Tue Aug 22 2006, 11:31PM
I still think using them as dividers and contributing data from a carefully controlled experiment would be worth much more to the forum then another Marx generator.
Re: HV coupling caps: Good for anything?
Sulaiman, Wed Aug 23 2006, 08:21AM
IF the internals are many small ceramic capacitors in a series/parallel mmc array
I would be tempted to put as many in series as neccessary
inside a Tesla Coil resonator from ground to topload.
This would;
A)
Allow the 'bottom' capacitor to be tapped off for an accurate measurement of topload voltage/waveform, and/or provide a voltage feedback signal
B)
Significantly lower the resonant frequency for easier electronic drive.
C)
You could drive the resonator from the bottom of the capacitor string.
Unlike driving from the bottom of the resonator,
when an arc forms, the input impedance would drop
allowing very 'hot' arcs.
AFAIK an untried/new topology.
A CFPR/Royer drive would be ideal for this.
Since there's over 3kJ worth of capacitors in there the rest could be used as an MMC
for SGTC or SSTC primary capacitor.
With over 3kJ of capacitance just about any hv project becomes viable;
Can Crusher, Railgun, nitrogen/CO2 Laser, CW/Villard multiplier, Marx etc.......
Sulaiman, Wed Aug 23 2006, 08:21AM
IF the internals are many small ceramic capacitors in a series/parallel mmc array
I would be tempted to put as many in series as neccessary
inside a Tesla Coil resonator from ground to topload.
This would;
A)
Allow the 'bottom' capacitor to be tapped off for an accurate measurement of topload voltage/waveform, and/or provide a voltage feedback signal
B)
Significantly lower the resonant frequency for easier electronic drive.
C)
You could drive the resonator from the bottom of the capacitor string.
Unlike driving from the bottom of the resonator,
when an arc forms, the input impedance would drop
allowing very 'hot' arcs.
AFAIK an untried/new topology.
A CFPR/Royer drive would be ideal for this.
Since there's over 3kJ worth of capacitors in there the rest could be used as an MMC
for SGTC or SSTC primary capacitor.
With over 3kJ of capacitance just about any hv project becomes viable;
Can Crusher, Railgun, nitrogen/CO2 Laser, CW/Villard multiplier, Marx etc.......
Re: HV coupling caps: Good for anything?
Steve Conner, Wed Aug 23 2006, 10:06AM
That would be a great experiment that would give us some new data on streamer behaviour. IOW: If you add a great big toroid to your coil, how does it change the spark length, as opposed to keeping a small toroid (or even taking the toroid off altogether) and using a capacitor string to bring the capacitance up to the same as the big toroid would have.
I always wanted to try it, but never found a cheap capacitor that could take the output voltages of my coils. The mini OLTC gave about 120kV, the DRSSTC 300kV and the OLTC2 600kV.
Steve Conner, Wed Aug 23 2006, 10:06AM
That would be a great experiment that would give us some new data on streamer behaviour. IOW: If you add a great big toroid to your coil, how does it change the spark length, as opposed to keeping a small toroid (or even taking the toroid off altogether) and using a capacitor string to bring the capacitance up to the same as the big toroid would have.
I always wanted to try it, but never found a cheap capacitor that could take the output voltages of my coils. The mini OLTC gave about 120kV, the DRSSTC 300kV and the OLTC2 600kV.
Re: HV coupling caps: Good for anything?
J. Aaron Holmes, Wed Aug 23 2006, 03:24PM
Well shucks, you all have me interested in the voltage measurement thing now Trouble is, I've got neither the cash nor the coiling experience to do much of that (yet). I suppose what I really need to do is collect some of this cool junk Seattle City Light loves to throw away, buy a beat-up old F150, and drive out to Cheesehead or some other Teslathon and hand the stuff out to people who can actually do stuff with it
Regards,
Aaron, N7OE
J. Aaron Holmes, Wed Aug 23 2006, 03:24PM
Well shucks, you all have me interested in the voltage measurement thing now
Trouble is, I've got neither the cash nor the coiling experience to do much of that (yet). I suppose what I really need to do is collect some of this cool junk Seattle City Light loves to throw away, buy a beat-up old F150, and drive out to Cheesehead or some other Teslathon and hand the stuff out to people who can actually do stuff with it Regards,
Aaron, N7OE
Re: HV coupling caps: Good for anything?
Steve Conner, Wed Aug 23 2006, 04:47PM
Buy one, gut it, and sell all the little green doorknob caps to us!
Steve Conner, Wed Aug 23 2006, 04:47PM
Buy one, gut it, and sell all the little green doorknob caps to us!
Re: HV coupling caps: Good for anything?
Sulaiman, Wed Aug 23 2006, 04:49PM
Aaron,
I'd like to try this experiment myself;
IF you get one and dis-assemble it I'd be very willing to pay postage to here (UK) for a nice string of capacitors.
For my present resonator I'd LIKE 1m (39") of capacitance (new unit !)
I dare say there are others here who would also love capacitors for postage costs -
especially from such a generous guy as yourself
If not, eBay is an option for you to get cash for other purposes.
EDIT....WOW! same thought within 2 minutes!
Sulaiman, Wed Aug 23 2006, 04:49PM
Aaron,
I'd like to try this experiment myself;
IF you get one and dis-assemble it I'd be very willing to pay postage to here (UK) for a nice string of capacitors.
For my present resonator I'd LIKE 1m (39") of capacitance (new unit !)
I dare say there are others here who would also love capacitors for postage costs -
especially from such a generous guy as yourself
If not, eBay is an option for you to get cash for other purposes.
EDIT....WOW! same thought within 2 minutes!
Re: HV coupling caps: Good for anything?
J. Aaron Holmes, Wed Aug 23 2006, 04:58PM
I'll go down there and have another look and ask if they'd just let me gut 'em. I don't think I have room for the porcelain. At least, not more than one! If I can get boatloads of doorknobs for uber-cheap, I'll report back. I'd be happy to just cover my costs if folks want them. I probably wouldn't be able to guarantee they all work, though!
Regards,
Aaron, N7OE
J. Aaron Holmes, Wed Aug 23 2006, 04:58PM
I'll go down there and have another look and ask if they'd just let me gut 'em. I don't think I have room for the porcelain. At least, not more than one! If I can get boatloads of doorknobs for uber-cheap, I'll report back. I'd be happy to just cover my costs if folks want them. I probably wouldn't be able to guarantee they all work, though!
Regards,
Aaron, N7OE
Re: HV coupling caps: Good for anything?
Dr. Drone, Wed Aug 23 2006, 07:34PM
Dr. Drone, Wed Aug 23 2006, 07:34PM
Re: HV coupling caps: Good for anything?
Marko, Wed Aug 23 2006, 08:03PM
[quote]
[/blockquote]
I tought that were strawberryes.
One has to see such an amount of expensive caps in one place
Marko, Wed Aug 23 2006, 08:03PM
[quote]
[/blockquote]
I tought that were strawberryes.
One has to see such an amount of expensive caps in one place
Re: HV coupling caps: Good for anything?
J. Aaron Holmes, Thu Aug 24 2006, 03:41PM
Wow, Christopher! You guys really scored a boatload of caps there!! I hope I'm as lucky! Those red ones look a bit beefier than what my friend got out of the last one of these he dissected. He got hundreds of them, but they were 20kV and 500pF. "Little green guys." Tragically, he sold most of them on eBay before I knew him. He's been contemplating building a TC MMC out of what he's got left, but hasn't done so yet.
I'm heading down to the salvage yard this afternoon and will report back. Will also be looking for some station post insulators. Last time I was there, I bought a bunch of random insulator-looking things at $5 a pop, and they later turned out to be 21kV lightning arrestors. Whoops! I haven't yet figured out how to get them open non-destructively, so they may become safety gaps
Regards,
Aaron, N7OE
J. Aaron Holmes, Thu Aug 24 2006, 03:41PM
Wow, Christopher! You guys really scored a boatload of caps there!! I hope I'm as lucky! Those red ones look a bit beefier than what my friend got out of the last one of these he dissected. He got hundreds of them, but they were 20kV and 500pF. "Little green guys." Tragically, he sold most of them on eBay before I knew him. He's been contemplating building a TC MMC out of what he's got left, but hasn't done so yet.
I'm heading down to the salvage yard this afternoon and will report back. Will also be looking for some station post insulators. Last time I was there, I bought a bunch of random insulator-looking things at $5 a pop, and they later turned out to be 21kV lightning arrestors. Whoops! I haven't yet figured out how to get them open non-destructively, so they may become safety gaps
Regards,
Aaron, N7OE
Re: HV coupling caps: Good for anything?
J. Aaron Holmes, Sun Aug 27 2006, 09:03PM
(bump)
Well, I went down on Friday and bought two of these. For only $50 each! I just couldn't turn them down for that price. They look almost new, and I was told they ought to be in fine shape; they were just taken out of service as part of routine maintenance. I looked all over them and couldn't find a part number, however. They were selling a couple of whole capacitive voltage transformers too ($250 ea) which use the same caps as I'm getting. In fact, I think the ones I'm getting were originally stacked on these PTs to double the voltage. I'll get the part number from the PTs and see if that leads me to the capacitor info.
The units are made by ABB. I pulled up the coupling cap literature from ABB (production units only) and they don't really reveal too much about the internals of the thing. Plus who knows whether the modern docs are any indication of what's in these older ones.
I'm picked them up this coming Friday (earliest I could trick one of my coiling friends with a pickup truck to help me haul them away), and will keep you all posted on what I find. I found some 6" casters at a local junk store yesterday, so whether or not I can use the guts of the thing, I definitely plan to put it on wheels and see about winding an oil-immersed TC secondary in it. That would sure be spiffy!
Regards,
Aaron, N7OE
J. Aaron Holmes, Sun Aug 27 2006, 09:03PM
(bump)
Well, I went down on Friday and bought two of these. For only $50 each!
I just couldn't turn them down for that price. They look almost new, and I was told they ought to be in fine shape; they were just taken out of service as part of routine maintenance. I looked all over them and couldn't find a part number, however. They were selling a couple of whole capacitive voltage transformers too ($250 ea) which use the same caps as I'm getting. In fact, I think the ones I'm getting were originally stacked on these PTs to double the voltage. I'll get the part number from the PTs and see if that leads me to the capacitor info.The units are made by ABB. I pulled up the coupling cap literature from ABB (production units only) and they don't really reveal too much about the internals of the thing. Plus who knows whether the modern docs are any indication of what's in these older ones.
I'm picked them up this coming Friday (earliest I could trick one of my coiling friends with a pickup truck to help me haul them away), and will keep you all posted on what I find. I found some 6" casters at a local junk store yesterday, so whether or not I can use the guts of the thing, I definitely plan to put it on wheels and see about winding an oil-immersed TC secondary in it. That would sure be spiffy!
Regards,
Aaron, N7OE
Re: HV coupling caps: Good for anything?
..., Sun Aug 27 2006, 10:58PM
If you do get them open I would love to get my hands on a pile of the caps
..., Sun Aug 27 2006, 10:58PM
If you do get them open I would love to get my hands on a pile of the caps
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