Film Capacitors come in two standard designs, a film-foil combination where plastic or paper films are interleaved with metal foils that serve as electrodes, or as a Metalized construction where film has aluminum or zinc deposited in it to serve as the electrodes.
Metalized film capacitors show there advantages where smaller applications are needed due to their smaller size and lower weight. Metalized capacitors also have a built in “healing” property where in the case of voltage stress the film will clear itself and heal the point of damage. Due to this “healing” property most metalized film capacitors are tolerant of overvoltage.
Circuits which require high currents may need a film-foil combination capacitor. The heavy foil of this combination offers low electrical resistance and excellent thermal dissipation preventing internal hot spots and optimizing the circuit efficiency.
Impregnated capacitors are recommended for high voltage circuits where corona may be a problem. Wax is suitable for a lower temperature application. For higher temperature application oil is a suitable impregnant. These capacitors can be either metalized or film-foil combination. Also, series wound units are used to prevent corona.
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