What is the self-healing principle of film capacitors

The self-healing principle of film capacitors can be specifically explained in the following aspects:

1. Automatic Reduction of Electric Field Strength  

When the dielectric of a film capacitor is subjected to an electric field strength exceeding its tolerance, breakdown occurs within the dielectric, causing charges to accumulate at the breakdown point. This creates a strong electric field in regions with high charge density. Under the influence of this strong electric field, a large number of electrons and holes are generated. These electrons and holes cause the dielectric to decompose into gases or ions, generating heat, which ultimately forms a thicker insulating layer around the breakdown area.

This insulating layer automatically reduces the electric field strength, further preventing current flow. Additionally, the charge cloud formed on or around the dielectric surface gradually weakens the electric field strength, allowing the capacitor's insulation state to recover automatically.

2. Automatic Isolation of Faulty Circuits  

When the capacitor dielectric breaks down, an instantaneous arc discharge occurs. This arc discharge causes the voltage between the capacitor electrodes to drop to zero, initiating a recharging process. If the capacitor selection and circuit design are improper, the inter-electrode capacitance may respond faster than the equivalent series inductance at this moment. This means that during the arc discharge, the capacitor will first recharge its voltage before reacting to the current, generating a high transient current that can easily damage the circuit or power supply. To ensure the normal operation of the circuit, a protective circuit is pre-designed inside the capacitor. When an arc discharge occurs, this protective circuit automatically isolates the faulty section, safeguarding the normal operation of the circuit.

3. Automatic Recovery of Dielectric Insulation  

When the capacitor dielectric breaks down, an instantaneous high-energy electric field is generated, which can rupture some molecular bonds within the dielectric. This disturbs the molecules, producing ions, free electrons, and free dielectric molecules. Simultaneously, the arc discharge generates a significant amount of heat, causing the dielectric to lose some molecular chains and reducing its insulation performance.

However, because the breakdown in film capacitors is localized—occurring only briefly and within a small area—the damage remains localized. After the instantaneous discharge, the heat naturally dissipates. During this process, the dispersed ions and free dielectric molecules are attracted by the electric field to the breakdown area, facilitating the spread of heat over a larger range. This mitigates the decline in insulation performance caused by the breakdown. As a result, the capacitor's insulation state can automatically recover under ambient conditions.

In summary, the self-healing property of film capacitors arises from the unique structure of their materials and the characteristics that automatically reduce electric field strength, isolate faulty circuits, and restore internal insulation after dielectric breakdown. This property not only enhances the reliability and service life of capacitors but also reduces the frequency and cost of maintenance.