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Re: Power Factor Caps
John and all,
As you have already guessed, utility PFC caps are built "like a tank"
since they must contend with brutal lightning and switching transients,
scorching summer heat, driving rain, and brutal cold. Well... maybe not
extreme cold in California. :^)
Older PFC caps used kraft paper and mineral oil or PCB's as the
dielectric system. Newer capacitors use kraft paper and a non-PCB liquid
impregnant, and newer ones now use Mylar or (even better yet!)
Polypropylene film and kraft paper as the dielectric system. Unless
specifically labeled with "No PCB's", most utility PFC's built in the
USA between 1935 and 1976 will most likely contain PCB's. PFC's built
prior to 1935 typically used mineral oil, and those built after 1976
typically use synthetic dielectric fluids. PFC's often come with
internal bleeder resistors to allow for safe handling after 1-5 minutes.
BTW, the bleeder resistors are NOT a source of significant loss for
Tesla Coil use. High ESR should not be a problem for these beasts.
The most likely problems with using PFC's in Tesla Coils are:
1. They may contain PCB's.
Since utility PFC's tend to be relatively large, they can contain a
significant amount (>3 pounds) of PCB's. This can present you, or your
estate, with a costly disposal problem. Worse yet, large PCB-containing
equipment (including pole pigs) can also become a collosal bureaucratic
"pain in the butt" if your local environmental agency discovers you
possess them. And if your capacitor case should rupture or spring a leak
inside your house or in your yard, panic could set in from your
neighbors, the local hazmat guys, the EPA... heck, your home might even
qualify as a Superfund site... :^). Because of the irrationality that
surrounds PCB's, many coilers simply won't fool with large PCB caps. And
thoses that do tend not to advertise the fact...
2. The capacitance will most likely be too high.
These capacitors are designed to provide bulk capacitance at 50 or 60
Hz. The smallest standard size for utility PFC's is 50 KVAR, which for
14.4 kV and 60 Hz means you've got a 0.64 uF cap. Now some coilers have
sucessfully opened the capacitor case and then re-wired the capacitor
buses to connect rolls in series. It can be a messy job, but if the
capacitor was obtained cheaply (or for free), it might be worth the
effort, especially if it's a kraft paper-polypropylene cap. Another
option is simply to remove the rolls, reconnect the capacitor rolls in
series, and the put them into a custom container. Since the rolls are
already impregnated, covering them with mineral oil (if necessary)
should work just fine.
3. The dielectric system may have relatively high RF losses
Earlier PFC caps used relatively lossy dielectric systems (particularly
at RF frequencies). Unless you have one of the newer polypropylene-kraft
paper caps, it's probably not worth the time and effort to rewire the
cap for TC use. However, PFC caps DO make GREAT energy storage caps for
filtering, Marx generators, exploding wires, DC coils, and other
interesting HV stuff...
Hope this helped!
-- Bert --
Tesla List wrote:
>
> Original Poster: "j. Grissom" <johngd-at-bellsouth-dot-net>
>
> has anyone tried utility power factor correction capacitors on a
> tesla coil? I have available to me a couple of units that are rated
> for 14.4kv primary duty. Rated in KVAR. I haven't converted this
> to uF yet. Has a BIL rating of 125KV which should be tough enough
> for coil use. They are large, probably knee-high and weight at
> least 100 lbs. Do these things have some fatal defect such as high
> ESR or high dielectric loss that would make them not work? I hate
> to lug one home and try to build a coil around it if it won't work.
> I see these things for sale on utility apparatus sites on the net
> really cheap so this would be a good resource if it works.
>
> John
>
> --
> John De Armond
> johngd-at-bellsouth-dot-net
> Neon John's Custom Neon
> "Bendin' Glass 'n Passin' Gas"