Image courtesy of KYOCERA AVX. Metallized film capacitors exhibit a self-healing property that significantly improves their lifetime reliability characteristics. Figure 4 depicts the basic process wherein a dielectric defect results in a high current, high-temperature short circuit that quickly demetallizes the surrounding area.
Unfortunately, this mechanism can be dificult to control, and in the worst case, a run-away process can result, causing the destruction of the entire capacitor in short order. To avoid this, KYOCERA AVX developed a controlled self-healing process in 1974 based on the segmentation of overall capacitance into elementary cells protected by fuse gates.
Aluminum electrolytics tend to be cost-efective in applications requiring high capacitance values at DC voltages less than 800V. These applications include DC-DC converters, motor starters, and frequency converters. When higher voltages are required, especially in non-polarized AC circuits, metal film capacitors are the only alternative option.
In high voltage, high energy applications such as electric trains and solar power grids, the safety and reliability of capacitors are paramount. Catastrophic failures and associated explosions or fires are unacceptable. Just as importantly, service lifetime and predictability for optimizing up-time are critical to the product's success.
This controlled self-healing technique is now the standard construction for all KYOCERA AVX’s film capacitor solutions, including dry, no free oil, and oil impregnated. these capacitors experience no As a result, catastrophic failure (short circuit).
Figure 1: Conventional aluminum electrolytic capacitor. Image courtesy of KYOCERA AVX. On the other hand, metal film capacitors rely on a metallized dielectric film to form the capacitive structure. Many film materials are available - most commonly, polypropylene and polyester.