RE: MMC cap bank

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>" <gary.lau-at-hp-dot-com>

I'm not sure I agree with this dismal assessment.  MMC caps are typically 
designed with voltage ratings governed by the cap's DC rating, not the AC 
rating.  The proposed cap's string rating was 25kV, a reasonable margin 
above the peak voltage from a 14.4kV power supply.  The difference between 
a pig and an NST application is the RMS current.  An MMC designed for a pig 
must handle higher current, so more parallel strings must be 
used.  Designing longer strings won't improve the ability to handle higher 
currents.  Longer strings of the same cap size will result in lower 
capacitance per string, so more strings will be required to achieve the 
desired final capacitance, but it would be more economical to just use 
shorter strings of smaller caps.

That said, I don't know if the proposed BC caps have a proven suitability 
for MMC's.  The price does seem attractive though!  I think Terry commented 
that they appear somewhat small compared to other similarly rated units?

Gary Lau
MA, USA

 >Original poster: "Dr. Resonance by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <resonance-at-jvlnet-dot-com>
 >
 >The rating you specified alone should tell you it won't work for a long
 >time --- perhaps short time until you start blowing them.
 >
 >The pig is 14.4 kV and you intend to run the cap string at 900V x 10 which
 >only equals 9 kV.  Failure is certain --- the only question is when.
 >
 >With NST's we use 13-14 caps per series.  With pole xmfrs I would recommend
 >around 16 caps per series as an absolute min.
 >
 >Less than this will eventually begin to failure.


 >> Hello all,  I'm constructing my first mmc bank. Cap's are .056 uf. each,
 >> 2500 vdc. 900 vac. each. 10 per string .0056 total per string, a total of
 >> 10 strings max. .056 possible, probably tap out a smaller value at first
 >> although. Cap's are digi-key # BC2048-ND, AC and pulse double metallized
 >> polypropylene film. Bleeders are 10 megohm 1/2 watt. Using 14.4 kv. 10 kva.
 >> pig, MOT. ballast on primary, asynchronous gap, speed is ajustable so it
 >> may be in synch. at some point. Will it last?  Comments? Thanks    Arcing
 >> in Wisconsin.......