Power capacitors-new developments

Capacitors are used in many applications ranging from traction, reactive power compensation through to furnace duties. To varying degrees many applications require capacitors with the highest available energy densities. Two examples include DC filter capacitors for traction applications where weight and volume of the traction convertor is always limited. Secondly high voltage reactive compensation where as demands on the electricity supply network change so the need for portable compensation which is easily relocatable becomes paramount. Solid foil dielectric technology, metallised film and segmented film are the major technology changes seen over the 15 year period. With each change so there has been a step increase in energy levels, primarily associated with increased stressing ofthe dielectric. The critical design parameters remain. For typical filter and resonant circuit applications these include voltage withstand, current carrying capacity, life expectancy, minimal unit inductance and surge discharge capability. Also of prime importance is ensuring the capacitors are adequately protected. As the market becomes ever more competitive so the need to increase capacitive output continues. Possibilities for future developments include changing the basic dielectric material, to increase dielectric constant whilst retaining acceptably low loses and improving the quality of the basic dielectric by either improving manufacturing processes or coating the dielectric film to eliminate pinholes.