Self-healing Characteristics Of Film Capacitors

There are two different mechanisms of film capacitor self-healing: discharge self-healing and electrochemical self-healing. Discharge self-healing occurs under high voltage, so it is also called high-voltage self-healing. Electrochemical self-healing also occurs under low voltage conditions, so it is called low-voltage self-healing.

1. Self-healing

Suppose there is a flaw in the film between two metallized electrodes, and the resistance is R. Depending on the nature of the defect, it may be a metallic defect or a semiconductor or poor insulation defect. When the defect is a metallic defect, at low voltage, the capacitor has already discharged self-healing. It is high voltage discharge self-healing only when the defect of semiconductor or poor quality insulation.

2. Electrochemical self-healing

This kind of self-healing occurs in film capacitors under low voltage. The mechanism of this self-healing is as follows: Suppose there is a defect in the dielectric film of the metallized organic film capacitor. After the voltage is applied to the capacitor, there will be a large leakage current through the defect, which shows that the insulation resistance of the capacitor is much lower Specified value in technical conditions.

Because film capacitors have a certain water absorption rate, and during the capacitor manufacturing, storage, and use, capacitors may be wet, and the leakage current may contain ionic currents or electronic currents. Therefore, a considerable part of the ion current is the O2- ion and H-ion current generated by the electrolysis of water. After O2- ions reach the AL metallization anode, they combine with AL to form AL2O3. With the increase of time, the AL2O3 insulation layer is gradually formed to cover and isolate the defects, so that the insulation resistance of the capacitor is greatly improved and self-healing is achieved.