Capacitor self-healing process and mechanism analysis

During the operation of metallized capacitors, due to dielectric defects or stupid points in the process of manufacturing, instantaneous high-current flashover occurs locally on the plate. The energy of this instantaneous large current will not destroy the insulation of the medium, but will only lead to the reduction of the metal layer of the plate in a very small range, and the process of returning to normal working state is called self-healing. This article introduces the mechanism of the self-healing process. Metallized capacitors are formed on the dielectric material by using high-vacuum evaporation equipment to coat the surface to form capacitor plates. Generally, zinc-aluminum composite metal layers can be evaporated on capacitor paper or film media.

The thickness of the medium is generally a few microns, and the metal layer is extremely thin. There is no way to measure the thickness of the metal layer. The thickness should be on the order of angstroms, which is the smallest ZZ in the length measurement unit. Since the thickness of the zinc-aluminum evaporation layer is very uniform, the thickness is expressed by measuring the volume resistivity of the metal layer during the production process. Because of the same material resistance and the same area, the volume resistivity depends on the thickness. Because there may be weak points in electric strength in the local area of the capacitor dielectric material, there may also be mechanical trauma or impurities in the manufacturing process.

When the capacitor is working, a local flashing arc occurs. The energy of this arc impact can volatilize a small range of metal layers around the defect, but it is not enough to break down or carbonize the dielectric material. The medium still maintains an insulating state. Due to the extremely small range of metal Volatilization, so that the original dielectric defect range is isolated from the plate, and the loss of the plate area in a small range has a very small reduction in the capacitance value, which can be ignored.

The entire capacitor returns to normal working condition. This process is called capacitor self-healing. The self-healing point on the metallized capacitor plate and the structural representation are shown in the figure below. The self-healing function is a unique feature of metallized capacitors, and capacitors with other structures such as electrode foils do not have this function.