Lifetime Improvement of Metallized Film Capacitors by Inner Pressure Strengthening

Metallized polypropylene film capacitors (MPPFCs) are widely used in pulse power systems for their characteristics of high reliabilities, high energy densities, and excellent pulse power handling capabilities. The teardown showed that the capacitance loss decreased gradually from the outer layers to the inner layers in a cylindrical MPPFC winding. This paper concentrates on the inner pressure in the MPPFC winding. First, the effects of the inner pressure on the self-healing and the lifetime are investigated. The lifetime can be extended by the inner pressure strengthening. Second, an inner pressure calculation formula is presented. The effects of the heat treatment and wrapped film on the pressure are considered. In addition, the heat treatment and wrapped films are chosen to strengthen the pressure. Finally, the experiments are designed to validate the effect of the lifetime improvement by the methods of the inner pressure strengthening. Results show that the lifetime can be extended by 30% with rational heat treatment and by 38% with rational design of the wrapped film.