The biggest feature of metallized paper dielectric capacitors is that they have a self-healing effect after being broken down, and can still work normally after the circuit voltage returns to normal. Generally, the paper dielectric capacitor is burnt after being broken down, and the two layers of metal foil are melted together at the place where the breakdown occurs, forming a short circuit. After the metalized paper dielectric capacitor is broken down, the metal film of the broken place evaporates at a high temperature, leaving only small holes in the insulation and no short circuit.
Paper dielectric capacitor is a capacitor composed of paper with a very thin dielectric as the dielectric, aluminum foil as the electrode, which is wrapped into a cylindrical shape, and then impregnated with a shell package or epoxy resin potting.
Paper dielectric capacitors are a class of capacitors with paper as the dielectric. In fact, the capacitor medium is not simply capacitor paper, but a composite medium impregnated with an impregnating material. This composite medium and the electrode plate are used to form a capacitor.
The capacitor paper and the electrode plate are wound into a core, and then impregnated (the impregnating material is polar or non-polar, solid, liquid and semi-liquid), and then sealed. Sealed forms are aluminum case filled with resin, iron case, high pressure and even ceramic case. Paper dielectric capacitors have large tgδ, so the application range is only in DC and low frequency circuits. Moreover, it is easy to aging. After aging, the dielectric strength of the capacitor gradually decreases with time. The capacitor has poor thermal stability, so the capacitance stability is not high, the operating temperature is low, and it is easy to absorb moisture. Therefore, good sealing conditions are required to ensure the quality of the capacitor.
Paper dielectric capacitors use two metal foils (tin foil or aluminum foil) as electrodes, then sandwich extremely thin capacitor paper between the two metal foils, roll them together into a cylindrical or flat cylindrical core, and then seal them in a metal case Made of insulating material (such as ceramic, glass glaze, etc.) in the shell. By changing the area of tin foil or aluminum foil, paper dielectric capacitors with different capacitance can be made.
Paper dielectric capacitors are divided into two kinds of winding methods: inductive and non-inductive. The inductive core is actually a strip coil with many turns, so the inductance is large. In the non-inductive type, the electrode foil is staggered to the two sides of the paper, so that the side of the foil strip protrudes from the outer edge of the paper strip, is wound into a cylindrical core, and the lead is welded. In this way, the turns of the electrode foil are shorted to each other, so the inductance is very small. This capacitor can be used at higher frequencies.
It is mainly used for bypassing, coupling, filtering, etc. in lower frequency circuits.