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Hi Steve,
That is correct. This means that the maximum peak-to-peak voltage swing
in a ringing application would be 50 + 10 = 60 kV. In a relatively
high-Q environment, such as a TC primary circuit, the peak charging
voltage should be no more than half of this, or 30 kV to avoid
accidentally overvolting the cap. Most Maxwell pulse capacitors have a
20% voltage reversal spec. A few "overbuilt" models go up to 80% VR, but
more highly-stressed, physically-smaller units may only have 5-10% VR.
An easy to remember rule of thumb is to use a pulse capacitor that has a
DC rating of at least 3X the maximum (worst-case) RMS output voltage of
your HV supply transformer. This should include any step-up voltage
coming from your Variac. For example, a tank cap driven from a 14.4 kV
pig at 280 volts will need a minimum DC voltage rating of
14.4*(280/240)*3 = 50.4 kV (or higher) to meet its design lifetime.
Most "Maxwell" branded pulse caps you'll find on the surplus market are
not self-healing, so overstressing them is considerably more risky (and
unforgiving) than with self-healing MMC capacitor arrays.
Bert Hickman
Woodridge, Illinois
Steve White wrote:
I want to confirm my understanding of the maximum VR (voltage reversal) specification. If the spec states a maximum VR of 20%, I assume that this means that the capacitor can safely handle a 20% reversal of the maximum DC voltage spec. For example, if I had a capacitor with a maximum DC voltage rating of 50 KV and a maximum VR of 20%, then the capacitor could safely handle up 10 KV of reverse voltage or -10 KV volts. Is my interpretation correct?
Steve White
Cedar Rapids, Iowa
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