High temperature, >200°C, polymer film capacitors

A number of polymer films were evaluated to determine the feasibility of a >200°C AC and DC capacitor dielectric. Small samples of film were checked for their dielectric properties, particularly dissipation-factor-temperature relations between 150°C and 300°C, electric strength, thermal and hydrolytic stability, and potential to be produced in large quantities in thin gauges. A 3M proprietary experimental film, FPE, was found to be the most promising with low dissipation factors between 150°C and 275°C. The criterion for the high temperature usability of this film was its performance in 0.4-μF to 1-μF capacitors as a film-film-foil and metallized film winding. The quality and production of FPE film were upgraded for the capacitor application. This was based on capacitor producibility from FPE film rolls and high temperature life tests under DC and 400 Hz AC stresses, and film producibility and tests. Capacitor failures were of the dielectric puncture type, apparently due to defects which could be minimized. A group of 0.5-μF capacitors was made for operation in a NASA power circuit at 20 kHz and 200°C. The 10-kHz to 100-kHz, dissipation factors of FPE film were very low at 175°C to 300°C, and were found to be very stable under these conditions of operation