Ultimate properties of the polypropylene film for energy storage capacitors

For current large projects to date, the mass production of new raw materials and the corresponding capacitors has not been completely achieved. Meanwhile, the classic products have been improved, especially those based on the metallized all polypropylene film. The properties of this film show a uniform range in terms of breakdown, with few thickness-dependent variations. For extended lifetime and high current values, the dielectric stress is far from the breakdown level of the polypropylene film. The evolution of the metallization-segmentation is described through the results obtained on three types of design. Conversely, for short capacitor lifetime and moderate currents, the stress can be situated in the breakdown area of the polypropylene film. Therefore, the working conditions must be precisely defined, especially in terms of charging time and hold time. In both cases, the inrush energy in the defect must be limited and controlled in order to avoid any secondary effect. The resistivities of the metallization play a significant role in controlling the high energy density products. The behavior of the galvanic contacts between the reinforced edges of the metallization and the metal spray is strong enough to allow the use of resistivities of several tens of Ohms per square unit. A comparison between resistivities shows that they can be used as a limitation tool in the self-healing process without undue influence on the current crossing properties. The results obtained on large energy units, ranging from 50 to 100 kilojoules, indicate the capacitors are completely safe, with an energy density of more than 2000 joules per liter for the short lifetime products. Some improvements regarding the purity of the resin and the surface treatment could increase the breakdown level to as high as 30%. The corresponding energy density could be increased to 3000 joules per liter.