Capacitors can create a variety of effects, and in some cases they can even repair themselves.
Capacitors are electronic components that regulate or modify the electrical current passing through them. Capacitors are part of most electronic devices --- especially those that deal with radio or audio frequencies such as phones, radios, televisions and recorders. A capacitor is basically two large area conductors (plates) separated by an insulator (dielectric). Capacitors can produce high-voltage spikes for spark plugs, stabilize ripples in power supplies and tune circuits to receive select radio stations.
How Capacitors Break Down
Capacitors break down if the dielectric is destroyed. Some capacitors have the ability to repair the dielectric if the destruction is not too bad. For some capacitors, this dielectric is grown as an oxide on the surface on one of the plates, and the dielectric can be regrown after a breakdown. In other capacitors, both plates and dielectric are submerged in a material that restores the dielectric after a breakdown. Both of these types of "self healing" capacitors are used for different purposes, are damaged in different ways and are healed by different processes. There is also a large group of capacitors that cannot heal themselves.
Electrolytic Capacitors
Electrolytic capacitors have a dielectric that is an oxide formed on the surface of one plate. Oxides are the results of chemical reactions that some materials have with the oxygen in the atmosphere. Sometimes oxides only form if a material is heated or if electricity is run through the material. The oxide on the plate of an electrolytic capacitor forms when electricity runs through the capacitor in one direction. If current runs through an electrolytic capacitor in the wrong direction it breaks down the dielectric which causes the capacitor to fail. Electrolytic capacitors heal themselves --- the oxide regrows --- if current, in the proper direction, is run through the damaged capacitor.
Oil Capacitors
With the enormous voltages --- and unpredictable environment --- of public utility lines, capacitors are particularly susceptible to damage. The large enclosed canisters that you see on power lines and in power substations are oil capacitors. The plates and dielectric are enclosed in an insulating oil that repairs breaks to both plates and dielectrics as soon as they occur. You do not even need to use a low current for a long time. Oil capacitors are truly self healing. Some high quality oil capacitors are small enough to be used in audio equipment --- like high quality amplifiers. These small oil capacitors use oil-soaked paper and Teflon composite materials. They are expensive, but they are also self healing.
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