Sunday, January 27, 2013

Some Basic Knowledge about Film Capacitor

The introduction of the metallized film capacitor

The films used in the metallized film capacitor are polyethylene ethyl acrylate, polypropylene, polycarbonate, etc., in addition, there are also the wound-type and the stacked type. This type of metalized film capacitors of film capacitor manufacturers has the role of the so-called Self Healing Action, which assumes a tiny part of the fragile quality of electricity sector and cause a short circuit, caused by a short circuit around the electrode metal part of the electrode, or short-circuit current due to the electrostatic energy of the capacitor brought, and lead to the dissolution of the larger area integration evaporated to recover the insulation, make the capacitor again return to the role of the capacitor.

metallized popypropylene film capacitor CBB15 4uF 500V

The features of metallized film capacitor

Metallized film capacitor that is taking the surface of the polyester film of the vapor-deposited layer of metal film as the electrode to take the place of the metal foil, because the thickness of the metal film layer is much thinner than the thickness of the metal foil, the wound volume is much smaller than the metal foil capacitance. The biggest advantage of metalized film capacitors is a "self-healing". The so-called self-healing property is if the thin film dielectric shows the phenomenon of short-circuit breakdown because the defects are in the presence of some points, and the condition of over-voltage, and the breakdown point metal layer may be in the arc under the action of an instant melting evaporated forming a small non-metallic area , the capacitance of the two pole pieces are re-insulated from each other and can continue to work, thus greatly improving the reliability of the work of the plastic film capacitor. Analysis from the above principle, metalized film capacitors should not have the short-circuit failure mode, while there will be a lot of short-circuit failure phenomenon in the metal foil capacitor.

The disadvantages of the metal film capacitor

Although the metal film capacitors have the great advantages as described above, but compared with the metal foil capacitor, there are the following two disadvantages: First, the capacity stability is poorer than a foil type capacitor, which is because in the long working conditions, the metallized capacitor is prone to capacity loss and the capacity will be reduced after healing, therefore, the metal foil capacitor should be better used in an oscillation circuit with the higher demanding in capacity stability. Another major drawback is the large current capacity is poor, which is because the metalized film layer is much thinner than the metal foils, and the ability to carry large currents is weaker. To improve this shortcoming of the metallized film capacitors, metalized film capacitors in high-current products in the manufacturing process has been improved, and the major improvement ways are: first, take the use of the double-sided metallized film as the electrode; second, increase the thickness of the metallization layer; third, the end face of the metal welding process improvements to reduce the contact resistance.

For film capacitors, dielectric materials are polyester film, polypropylene film and the dielectrod is envaporated metal layer or Aluminum foil or Zine-Aluminum foil. And the construction is wound or stacked.

This article is come from:

No comments:

Post a Comment