The main cause of failure of metallized film capacitors

1. Partial discharge

Due to the existence of tiny air gaps in the medium during processing, the metallized capacitors “over-self-healing” cause air gaps, resulting in partial discharge of metallized film capacitors under high voltage. The inside of the capacitors will quickly generate a large amount of heat, which is too late to be emitted. Further destruction of the surrounding medium, partial discharge is intensified, forming a vicious circle;

2. Loss of capacitor temperature rise

An ideal capacitor is dissipated during operation, but due to dielectric losses and the presence of metal resistance and contact resistance within the capacitor, the capacitor exhibits significant configuration characteristics. When there is a load, the metallized film capacitor is heated, and the heat is dissipated to the surrounding environment through the appearance of the capacitor, and a temperature gradient is established from the middle to the outer surface. When the heat is generated, the heat is balanced; when the heat is large, The heat dissipation cannot be balanced, and the temperature of the capacitor rises, causing failure, causing expansion, deformation, cracking of the outer casing, melting of the film into agglomerates, and serious phenomena such as burning;

3. Moisture is the main cause of degradation of the electrical performance parameters of film capacitors. This is because the molecules have a strong diffusion capacity, and the water medium constant is very large, and the loss is also large, resulting in a sharp deterioration of the electrical properties of the capacitor, such as a decrease in insulation resistance and compressive strength, an increase in dielectric loss tangent and a change in capacitance. . Especially when the ambient temperature rises, the diffusion capacity of water molecules is enhanced. Therefore, the high temperature and high humidity environment (such as 85 ° C, 85 percent RH) has a more significant effect on the electrical performance of the capacitor, resulting in product failure rate. Increased, reliability is reduced.