GENERAL INFORMATION Plastic film capacitors are generally subdivided into film/foil capacitors and metallised film capacitors. The following description gives brief information about their technical features.
FILM/FOIL CAPACITORS Film/foil capacitors generally consist of two aluminium foil electrodes with plastic film material used as dielectric. In order to guarantee the necessary safety and reliability of a capacitor it is essential to use a sufficient film thickness. Typical advantages that relatively large film/foil capacitors have over smaller metallised capacitors is their higher insulation resistance, their better capacitance stability and their good current carrying capability. High voltage and good pulse handling capability are additional features of these capacitors. Lead connections are made by means of welding.
METALLISED FILM CAPACITORS In contrast to film/foil capacitors, where aluminium foils are used as electrodes, the electrodes of metallised film capacitors consist of a thin metal layer (0.03 micron thickness, approx.) which is vacuum deposited on the dielectric film. The connection of metallised capacitors is accomplished by means of a metal spraying process and by welding the leads on to the sprayed ends. The main advantages of metallised capacitors are: 1) relatively small dimensions, a result of vacuum deposited electrodes, and, 2) self healing property. Owing to the self healing property, relatively thinner films can be used for metallised capacitors than film/foil capacitors.
DC CAPACITOR
A capacitor designed essentially for application with direct voltage.
AC CAPACITOR
A capacitor designed essentially for application with alternating voltage.
CLIMATIC CATEGORY
Indicates the conditions applicable to climatic testing of capacitors as per the relevant standards. It is indicated as a combination of test temperatures for cold proof, heat proof and test days for damp proof (steady state) which the capacitor will withstand. The category = XX / YYY / ZZ XX = Test temperature for cold proof YYY = Test temperature for heat proof ZZ = Test days for damp proof
CATEGORY TEMPERATURE RANGE
Denotes the range of ambient temperature for which the capacitor has been designed to operate continuously. This is defined by the temperature limits of the appropriate category.
RATED TEMPERATURE
The maximum ambient temperature at which the rated voltage may be continuously applied.
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