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Re: Capacitor voltage - AC or DC



Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

Somehow, someday, somebody, has to do something... :-))

Probably the "last unknown" of MMCs is how long the (CD 942C20P15K) will tolerate say 60Hz at 6000Vp-p....

Maybe do a bunch of different voltages to make a nice graph of 'lifetime vs. over voltage'...

That would tell us all we still want to know...

Cheers,

        Terry



One usually overrates the cap for AC use. I suggest Erms x 2 as a correct DC rating, so with your 15 kV AC xmfr, for a near bullet proof cap bank, you want a cap bank rated at 30 kV DC.

If you are using 0.15 uF 2 kV caps in your strings then each 15 cap string would be rated .01 uF at 30 kV DC.

With a 30 mA xmfr you need approx .014 uF capacitance so you cheat a bit and use 11 caps in each string. This gives you a single string rated .0136 uF at 22 kV DC which will work fine with your 30 mA xmfr. You try to avoid a .01 uF match with the xmfr as the cap bank might resonate with the xmfr and damage the xmfr. Going a bit higher usually works very well. 1.2-1.3 x Cres.

Dr. Resonance