Implications of Advanced Capacitor Dielectrics for Performance of Metallized Film Capacitor Windings

A range of high dielectric capacitor films is under development with the objective of improving the energy density of pulsed discharge capacitors. A substantial change in capacitor film dielectric constant has implications for capacitor design and function. This paper develops formulas for equivalent series resistance (ESR) and equivalent series inductance (ESL) of a capacitor winding as a function of material properties and winding design. A numerical approach is used to investigate the frequency-dependent ESR and ESL, after which a formula is developed for the inductance based on a resistive/capacitive current distribution in the winding. The analysis is carried out for a metallized film winding in which the return conductor is brought through the center of the core on which the film is wound so that both connections are made from the same end of the capacitor with minimal inductance. The implication of moving to high dielectric constant film is investigated on the basis of this analysis with the result that for direct film replacement and fixed winding capacitance, the ESR will increase in proportion to the film dielectric constant and the inductance will decrease slightly.