Ultimate properties of the polypropylene film for energy storage capacitors

Summary form only given, as follows. Today, for current large projects, the industrialization of new raw materials and the corresponding capacitors is not completely achieved. In the meantime, the classic products are improved and especially those based on the metallized all-polypropylene film. The properties of this film show a homogeneous range, in term of breakdown, with few variations depending on the thickness. For long lifetime and high current values, the dielectric stress is far from the breakdown level of the polypropylene film. The evolution of the couple metallization-segmentation is described through the results obtained on three types of design. On the other hand, for short 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 term of charging time and hold time. In both cases, the inrush energy in the defect must be limited and controlled in order to prevent any secondary effect. The resistivities of the metallization play a significant role to secure the high energy density products. The behaviour 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 some resistivities shows that they can be used as a limitation tool in the self-healing process without too much influence on the current crossing properties. The results obtained on large energy units, ranging from 50 to 100 kilojoules, lead to completely safe capacitors, 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 in a range of 30%. The corresponding energy density could be increased to 3000 joules per liter.