Capacitors

Capacitor classes

There are different classes of capacitors:

1. 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.
   
2. High voltage capacitors
3. Energy storage capacitors
   A full section of this site is dedicated to supercapacitors.
   Ceramic capacitors are often proposed to fulfil this function.
   
4. Starter capacitors
5. Filtering capacitors
6. Discharge capacitors

Capacitor technologies

There are several different technologies which are used to build capacitors:

• Film foil
  

  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.

  


• Gas


• Electrolytic


• Electrochemical (= Supercapacitors = Ultracapacitors = Double layer capacitor)
• Ceramic (Ferroelectric)

Source: Garmanage: Roland Gallay