What Is the SH Capacitor?

By David Stewart

It is possible to classify film capacitors into three broad construction categories -- mixed technology capacitors, metalized film capacitors and foil or film capacitors. However, metalized film capacitors are more advantageous compared to their foil or film capacitor cousins because of the former's unique and exclusive self-healing property. A self-healing capacitor can repair itself if the electrodes expose themselves to each other. The thinness of the foils used in this capacitor enables this self repairing.

Metalized Film Capacitor

In metalized film capacitors, or self healing capacitors, a thin layer of metal vacuum replaces the aluminum foils. The film itself contains the deposition of the metal vacuum. The thinness of the metalized film ranges between .02 and .05 micrometers and it becomes see-through or semitransparent if you hold it up against a light. The film is usually made out of zinc or aluminum.

Advantages of Self-Healing Capacitors

The two main advantages are the self-healing or self-repairing property and the reduced physical size of the capacitor. When a self-healing phenomenon takes place, it lasts for less than 10 microseconds and only a tiny percentage of the stored energy gets dissipated. The capacitors continue to operate in the occasion of the metal foils exposing themselves to each other, because the foils vaporize as a result of the combination of the fault area's high energy density and the thinness of the foil. Some other advantages include low to medium capabilities of handling pulse, low losses, wide range of operating frequency and small size.

Places Where Self-Healing Capacitors Work Best

Self-healing capacitors are cheaper, more pocket friendly and therefore suit a tight budget. These capacitors work best in the heavily overloaded rural and urban distribution lines where power is always supplied at low voltages, in the suburban areas where distribution lines are subjected to moderate load variations and voltage fluctuations and in the automatically controlled capacitor banks that have built-in current-limiting chokes and correction controls for over current, under voltage and over voltage.

Capacitors in the Future

With the rapid pace of technological advancement, research and development, it is a matter of time before supercapacitors solve the problems of brake energy storage in railway locomotives. It will take two to seven more years to develop supercapacitors that will be useful for efficiently operating the starting systems of pallet trucks, elevators, industrial applications, hybrid electric cars and diesel engines, as well as urban light rail and diesel electric vehicles.