Dielectric Breakdown and Capacitance

[DragonPetter]

If a capacitor's dielectric partially breaks down, as in some of the material has ionized and acted as a conductor, will there still be a capacitance to the component?

Say its a high frequency AC signal on a capacitor with a small part of its dielectric material in a breakdown state. My understanding would be that the capacitor would still have some capacitance and capacitor properties, but now its leakage would be increased.

Now the question is, will its capacitance be different or change when some of the dielectric has been broken down?

 

[NascentOxygen]

Hi DragonPetter. If the capacitor is tubular, with the sheets of foil rolled into a cylinder, then I expect a breakdown could occur between a some layers without erupting through the whole lot. So you would have a reduced capacitance but now with a resistance across it.

 

[DragonPetter]

Thanks, this is what I was hoping for.

Now to measure the change in capacitance, many meters use a charge-discharge time measurement, and I would guess that the leakage current will make the capacitance measurement wrong, so that you are not accurately measuring the change in capacitance, yes?

 

[NascentOxygen]

Sounds like it won't work. You'd need a bridge, and separately balance out reactance and resistance.

 

[DragonPetter]

Sounds like it won't work. You'd need a bridge, and separately balance out reactance and resistance.

Cool, that's what I'm planning to use, a wien bridge. The actual thing I'm looking at is not really a capacitor, but I'm considering it one for my measurements.