Evaluation of surface alteration of polypropylene film for power capacitors

Abstract

In polypropylene film insulated power capacitors, the surface alteration of the polypropylene film is critical to the electrical performance of the capacitors. Currently, the industry uses space factor to characterize the surface alteration. In this study, the authors investigated the surface alteration of three different polypropylene films used for power capacitors with a Keyence VK9700 3D laser microscope. The three polypropylene films have similar space factor values, similar nominal thickness and film surface alteration requirements. The study finds that the three polypropylene films have many significant differences in the morphology of the surface alteration structure and values of roughness parameters which indicate the limitations of the space factor methodology in fully characterizing surface alteration. The results show that the VK9700 laser microscope can provide much clearer film surface pictures and can provide much more surface alteration information than the ordinary optical microscope.

Influence of voltage on the H‐bridge of a large capacitor bank

“…where A is the effective area of the aluminum foil. When a voltage is applied, because the thickness of the oil changes, the equivalent dielectric constant becomes as in (9), and the capacitance becomes as in (10):…”

“…A space factor is used to evaluate the roughness in capacitor manufacturing , but it cannot provide detailed information of the surface of a PP film. Laser microscopy is useful to get clear film surface pictures . Figure shows the surface of a roughened PP film.…”

“…The condition of a PP film surface may be quite different even if the space factors are closed. The size and the thickness of the domains on the surface of the same piece of PP film are distributed over a range .…”