Early damage to capacitors is mostly due to manufacturing reasons. High voltage capacitors are usually composed of multiple elements in parallel, each element is made of aluminum foil as electrode, the solid medium is placed between the electrodes and wound. The polar plate area of the element is very large because of raw materials and manufacturing process, there may be impurities and mechanical damage in the medium. Pinhole, low cleanliness and other problems, this has become the inherent hidden trouble of the capacitor. In the system due to various causes of overvoltage, overcurrent and high and low temperature around the effect, these weaknesses will cause dielectric breakdown. The breakdown usually produces sparks and further expands the range to form a multilayer short circuit or even a short circuit of the entire component.
The voltage on the breakdown element in series will rise, and the group of components connected in parallel will be short-connected, thus the voltage on the remaining series group will rise, and the current passing through each element will also increase. It will lead to the rapid aging of various components, increase heat, at the same time under the action of higher voltage will also produce a partial discharge at the edge of the plate. In addition, the discharge of breakdown point will make the impregnating agent give off a large amount of gas, after a certain time, the whole series of components in series with the fault elements will be broken down one after another. There will be a new series group will be short, the number of series groups will be further reduced, element voltage further increased, the phenomenon of overcurrent is more serious, the dielectric further deterioration, the further increase in temperature will increase the arc. The impregnating agent further releases the gas, thus causing more and more damage to the components and more and more expansion of the case.
In this case, the protection fuse relay will be removed in time to the fault capacitor, if not removed further breakdown will form a strong arc in the case. Other shunt capacitors and system energy, in a very short period of time will make the capacitor medium aging, expansion, and finally lead to box shell expansion, serious will explode. This kind of accident is irrevocable to the user, it belongs to the early damage of capacitor, the period is usually about one year. As a manufacturer of capacitors, we should pay more attention to the quality and strengthen the testing methods in order to reduce the early damage rate.