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chief
National Hazard
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Maybe you're right somewhat. But look at those massive connections: 100's of kA will pass easily through ; internal resistance probably is minimized
too. Such a one is definately more suitable than some small electrolytic ; I bet that internally it's massively parallel-connected, which means low
inductance and fast discharge ; besides: When thinking about what's up when such a one fails in an electric locomotive (which my ones are for) or in a
big factory, then probably it's a stable construction, since shorts happen once in a while.
All those electrical networks are built with short-circuit-currents of 10's of kA in mind; even a 16-A household fuse is built so it can break at
least 6 or 10 kA of short-circuit-current ... .
There's another factor: The capacitor is massive, so any forces will be distributed over nearly the entire volume of the thing: Mechanical damage to
the capacitor may probably only happen at the internal connection-zones, should these be too weak.
The internal charge is distributed over much material with such non-electrolytics, and the nice thing about oil-dielectric is that it's
self-rearranging, no weaknesses due to repetitive strong discharges ; in fact fluid dielectrics are probably the best choice for such abuses ...
One thing that comes to my mind: Somewhere I read, that oil-capacitors have also the advantage of surviving an internal breakdown ... ; not sure if
that's true fur such big ones too ...
But staying away from the experiment, and remote-controlling everything (maybe some strong relay ...), is a must ! Any circuitry may be accelerated to
any velocity ; in power-electric engineering people wear bullet-proof clothing, because in case of a short the material may get's it's 1-2 km/s (!)
...
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woelen
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If you use capacitors for discharge experiments, then you really need capacitors made for that purpose. The ones, I have shown in this thread are made
for this purpose. A very fast discharge imposes a strong mechanical shock on the capacitor. The field between the plates suddenly drops from a large
value (many MVolts/m) to almost 0 and the attractive forces, associated with the strong potential difference between the plates suddenly disappears
and that gives increadible mechanical strain (like hitting with a hammer on it). Capacitors not especially constructed to survive these strains
quickly are broken (after at most a few tens of discharges).
The capacitors I have were intended to be used in special high power pulse laser systems.
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chief
National Hazard
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And I say: A big oil-capacitor has the forces distributed over a large amount of material, so each bit of material only gets a relatively small share
of the abuse ; .
What can happen internally: The dielectric (oil) can, upon release of the charge, suddenly get it's tiny bit of expansion, after the compression by
the coulomb force ; that's not much.
The electromagnetic forces are not big for each pair of plates ...
But probably with other types of capacitors the failure can be quite probable:
==> Any solid dielectric may just get too worn after a while ;
==> any high charge density (electrolytics) will subject too little material to the forces, with thereby faster mechanical response of the material
and greater mechanical stress ...
But a big oil-capacitor ? With only 10 microFarad per liter of volume ? The electrolytic has, for the same volume, maybe 1 Farad ... ; _that's_
stress, 100 000 times higher ...
It's as with other things: A big enough mass maybe can take it ... ?
But anyhow: Staying away from the discharge is a must, as mentioned above: 1 km/s of circuitry-speed (some piece of wire ...) may be no
over-estimation ...
[Edited on 7-2-2009 by chief]
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Texium
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Thread Moved
19-11-2023 at 12:52 |
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