What should be paid attention to when the film capacitor is tested for withstand voltage

The film capacitor is a capacitor in which a metal foil is used as an electrode, and a plastic film such as polyethylene, polypropylene, or polycarbonate is stacked from both ends and then wound into a cylindrical shape. In the early production process of film capacitors, manufacturers generally conduct AC withstand voltage tests on components. The specific process is to apply an AC voltage to the capacitor on the fixture of the automatic test sorter, and then check whether the leakage current is qualified.

However, since the dielectric material of the capacitor is not completely uniform, the electric field distribution will not be completely uniform. If the AC withstand voltage test is performed, it may cause thermal breakdown or excessive heat formation in the field where the field strength is too high. Hidden danger of media damage. Relevant research on various practical applications shows that the AC withstand voltage test contains the property of thermal breakdown. The higher the temperature, the lower the withstand voltage, and the key is that the film capacitor without breakdown may also cause local overheating damage. The testing of film capacitors is naturally required to detect product problems without causing internal damage.

The DC withstand voltage test method is similar to the AC withstand voltage test except that the external AC power supply is replaced with a DC power supply, but the principle is completely different from the AC withstand voltage. Because the distribution of AC and DC voltages in the medium is different, the DC voltage is distributed according to the conductance, which reflects the possibility of overvoltage in some parts of the medium; the AC voltage is reflected in the film capacitor part. In the case of voltage, the dielectric strength of the medium under DC voltage is higher than that under AC voltage.