Metallized film for electrical capacitors having a semiconductive layer extending entirely across the unmetallized margin

摘要

A film capacitor in which the unmetallized margin is provided with a semiconductive layer. The layer provides a parallel resistive path within the capacitor, itself, obviating the need for an external resistor. It also grades the electric field across the margin, i.e., makes the field more uniform, thus allowing the margin to be made narrower without electrical breakdown, permitting a reduction in the physical size of the capacitor. A refractory, semiconductive layer is provided between the metal layer and the dielectric film. The refractory layer accelerates the self-clearing process, by insulating the underlying dielectric film from the heat generated by the vaporizing metal, thus hastening vaporization and reducing the tendency of the dielectric film to carbonize. As a result, faults are cleared with substantially less energy consumption. Preferably, the refractory layer is also semiconductive, to reduce field emission effects, and thereby decrease the frequency of faults in the dielectric film.