Film capacitors for industrial equipment

Safety

A self healing metalized film capacitor is called SH (Self Healing) capacitor.
Self-healing means that when a part of the film suffers electrical breakdown, a small minute area of the electrode adjacent to the breaking point disappears, instantly restoring the function as a capacitor.

Even if a local electrical breakdown occurs in the dielectric of SH capacitors, the insulation of the broken part recovers due to self healing performance of capacitors. However, when self-healing occurs repeatedly such as at the end of life and when damage increases, even if the self-healing function stops working, large fault current does not flow because of the resistance of the vapor deposition electrode.
However, if it is used in this state as is, the internal pressure of the case will gradually increase due to the generation of gas in the faulty part, and the case may eventually burst, leading to secondary damage.
For this reason, as a protection device, we use a safety device that cuts off the current by using the deformation force of the case, or an abnormal pressure detection switch that detects increase in internal pressure, or a safety mechanism that opens the current path of the faulty area of the element.
(Please see the figure below for the structure and operating principle of safety devices and security mechanisms.）

Structure and operating principle of safety devices

Method using case deformation force