Dielectric Breakdown and Capacitance

In summary, the experts in the conversation discussed the effect of a partial breakdown of a capacitor's dielectric on its capacitance. They agreed that the capacitor would still have some capacitance and capacitor properties, but with increased leakage due to the breakdown. It was mentioned that if the capacitor is tubular, the breakdown may occur between layers, resulting in a reduced capacitance. To accurately measure the change in capacitance, a bridge would be needed to balance out reactance and resistance. The use of a wien bridge was suggested for this purpose.
  • #1
DragonPetter
830
1
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?
 
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  • #2
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.
 
  • #3
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?
 
  • #4
Sounds like it won't work. You'd need a bridge, and separately balance out reactance and resistance.
 
  • #5
NascentOxygen said:
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.
 

1. What is dielectric breakdown?

Dielectric breakdown is the process of an insulating material, or dielectric, losing its ability to resist the flow of electricity and becoming conductive. This can occur when the electric field exceeds a certain threshold, causing the electrons in the material to become more mobile and allowing current to flow through it.

2. How does dielectric breakdown affect capacitance?

Dielectric breakdown can significantly decrease the capacitance of a capacitor by reducing the amount of charge that can be stored in the dielectric material. This is due to the breakdown of the insulating material, which decreases its ability to hold an electric charge.

3. What are some common causes of dielectric breakdown?

Some common causes of dielectric breakdown include high voltage, high temperatures, mechanical stress, and exposure to chemicals or radiation. These factors can weaken the insulating properties of the dielectric material and lead to breakdown.

4. How is dielectric breakdown measured?

Dielectric breakdown is typically measured by applying a high voltage to the material and monitoring the resulting current flow. The breakdown voltage, or the voltage at which the material begins to conduct electricity, can then be determined. This measurement is important in determining the maximum voltage that a capacitor can withstand before breaking down.

5. What are some applications of dielectric breakdown and capacitance in science and technology?

Dielectric breakdown and capacitance play important roles in many areas of science and technology. Capacitors are commonly used in electronic circuits to store and regulate electrical energy, and dielectric breakdown is a crucial consideration in designing and testing these circuits. Dielectric breakdown also has applications in materials science, as it can be used to study the properties of insulating materials and to detect defects or weaknesses in them.

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