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DINGFENG CAPACITOR - - What are the reasons for the failure of metallized film capacitors?

Issue Time:2020-07-14


A metallized film capacitor is a metallized film capacitor composed of a double-sided metallized polypropylene film and a non-metallized polypropylene film that are rolled or laminated.

 

The film capacitor has many excellent characteristics, so it is an excellent capacitor. Its main characteristics are as follows: non-polarity, high insulation resistance, excellent frequency characteristics (wide frequency response), and low dielectric loss. Based on the above advantages, film capacitors are widely used in analog circuits. Especially in the signal cross-connection part, capacitors with good frequency characteristics and extremely low dielectric loss must be used to ensure that the signal will not be too distorted during transmission. Among all the plastic film capacitors, polypropylene (PP) capacitors and polystyrene (PS) capacitors have the most significant characteristics. Of course, the prices of these two types of capacitors are relatively high. However, in recent years, in order to improve the sound quality of audio equipment, the parts and materials used have become more and more advanced. Price is not the most important consideration. Therefore, in recent years, the frequency and quantity of PP capacitors and PS capacitors used in audio equipment have also increased. Higher. Readers can often see XX brand equipment, how many XX brand-name PP capacitors or PS capacitors are used as an endorsement of sound quality. This is the reason.

 

What are the main failures of metallized film capacitors?

 

1. Partial discharge caused

 

Due to the small air gap in the medium during the processing, the metalized capacitor "over-healing" causes the air gap, which causes the metalized film capacitor to produce partial discharge under the action of high voltage, and a large amount of heat inside the capacitor will be quickly dissipated before it is too late. The further destruction of the surrounding medium will increase the partial discharge and form a vicious circle.

 

2. Capacitor temperature rise caused by loss

 

An ideal capacitor does not dissipate quantity during operation, but due to dielectric loss and the existence of metal resistance and contact resistance inside the capacitor, the capacitor exhibits obvious configuration characteristics. When there is a load, the metalized film capacitor heats up, and the heat is dissipated to the surrounding environment through the surface of the capacitor. A temperature gradient is established from the middle to the surface. When the heat is small, the heat is balanced; when the heat is large, The heat dissipation cannot be balanced, and the temperature of the capacitor rises, leading to failure, causing the shell to expand, deform, crack, and melt the film into agglomerates. In severe cases, burning may be found. For this reason, loss is the root cause of heat generation and the main factor causing the failure of metallized film capacitors.

 

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