Film capacitor safety and insulation resistance

1. Film capacitor safety

The film capacitor uses a certain proportion of oil wax or sulphur hexafluoride as the impregnating agent, and the impregnating agent is poured into the capacitor shell by vacuum impregnation, which can effectively eliminate the partial discharge phenomenon at the edge of the core, and the crystallite after curing The wax forms a stress zone outside the core. When the component self-healing, due to the existence of certain stress, it can quickly extinguish the arc, preventing the evaporation zone from expanding and self-healing and causing component accidents. Compared with the liquid impregnating agent, the oil wax impregnating agent has stable performance, does not burn, and effectively solves the oil leakage problem.

In the event that the film capacitor fails due to self-healing, the internal metallized film is softened by heat and deflated to cause the capacitor to expand, and the safety device can cut off the power supply in time to protect the entire device. There are many types of safety devices, such as mechanical and electrical types. The fuse of the film capacitor is integrated with electric fuse and has a dual function. It is placed inside the capacitor case, and the fuse is used to activate the fuse and cut off the power. In the event that the mechanics insurance is out of control, the electrical insurance is activated immediately, and the power supply is also cut off to protect the entire device.

2. Insulation resistance of film capacitor

The insulation resistance of a film capacitor refers to the ratio of the voltage applied across the capacitor to the leakage current, that is, R = U / IL. R is the insulation resistance, U is the voltage, and IL is the leakage current of the film capacitor. There may be many people who don't know what is the leakage current of the film capacitor. When the leakage current of the film capacitor applies the rated DC working voltage to both ends of the film capacitor, we will see that the change of the charging current for charging the capacitor starts to be very large, and the current will follow. Decline with time, reach a relatively stable state when it reaches a certain value, and the magnitude of this current is called leakage current.

Therefore, the capacitance of the film capacitor is C=Q/U, Q is the charge amount, and U is the voltage applied across the capacitor. Combined with the above formula, R = Q / (C * IL) can be obtained, so we can know that the larger the capacitance of the film capacitor, the smaller the insulation resistance, the smaller the capacitance of the film capacitor, and the greater the insulation resistance.