High power capacitors
a) There are capacitors which are used in power inverter to filter the high frequencies (DC-link)
or the harmonics (Resonant filter). The main solicitation on these capacitors is a DC voltage with a superimposed ripple.
b) There are capacitors for the correction of cos φ factor of the electrical network.
The solicitation is AC.
There are several different technologies which are used to build capacitors:
The electrodes are made of aluminum foils of about 5 micrometers.
The dielectric is made of 2, 3 or even 4 films in the case of paper to compensate the inability of this technology
to control breakdown with selfhealing. The main polymers used are
polypropylene (PP), polyethylene terephtalate (PET, also called polyester in the capacitor domain)
or polyethylene naphtalene (PEN).
Metallized film (Gas and oil impregnated)
The dielectric is made of 1 or 2 film layers. The electrode is a very thin metal (Al, Zn or AlZn) layer (200 nm)
deposited on the film surface. In the case of a dielectric failure this metallization can evaporate thanks to the high currents
around the breakdown area between the electrodes. The metallized capacitor is selfhealing.