Dingfeng Capacitor -- What is the cause of failure of metallized film capacitors?

Nov 20,2019

A metallized film capacitor is formed by winding or laminating a double-sided metallized polypropylene film and a non-metallized polypropylene film.


Film capacitors are excellent capacitors because of their excellent characteristics. Its main characteristics are as follows: no polarity, high insulation resistance, excellent frequency characteristics (wide frequency response), and low dielectric loss. Based on the above advantages, the film capacitor is used in a large amount on the analogue circuit.


What are the main failures 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 exacerbated, 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 burning phenomena such as severe. For this reason, the loss is the source of heat, which is the main factor causing the failure of metallized film capacitors.



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