Re: [TCML] Intro and questions / MMC

[Finn Hammer <f-h@xxxx>]

Dunnsept?

It is customary to mention *one`s* name in this group, and welcome by 
the way.

I have used the 940C12W1P5K-F. ( 1.5µF 1200V ). In an OLTC with only one 
primary turn, which means high peak currents.
I can find the exact data if required, but the point is that if you make 
sure not to exceed the peak and rms current rating of the caps, then you 
are on safe ground.
The voltage rating can be exceeded to some extent, in that respect the 
caps are more forgiving.

The fault mode of these caps is as follows:

Over voltage will puncture the dielectric, and evaporate the thin 
metalization on the intermediate electrode. This leaves a non-conductive 
area around the hole large enough to make further discharge trough the 
hole impossible.
This is called self healing, and if this over voltage condition is not 
corrected, the cap will eventually drop in value and fail.

If the RMS current rating is exceeded the cap will heat and the 
dielectric will melt, which will lead to breakdown. An autopsy will 
reveal the melted mess.

If the peak current rating is exceeded the end caps will blow off, and 
the cap will fail in a very obvious and visible way.

So to chose the right cap, you need to calculate peak and rms current in 
your tank circuit.

Hope this helps.

Cheers, Finn Hammer

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