A Classical Capacitor Equivalent Circuit with Dependent Values

Formulae relating equivalent series resistance and capacitance of the traditional capacitor equivalent circuit, to frequency and the physical parameters of a capacitor are demonstrated. Spiral-wound cylindrical capacitors without schooping end-spray connections were used to model metallized film disconnected from direct connection to the schooping in corroded capacitors. The simple formulae for equivalent series resistance and capacitance, derived empirically from the diffusion equation modeling, were found to accurately reproduce experimental results for model experimental capacitors. Source or connection impedance was found to accurately model a rise in dissipation factor at higher frequencies. Application of the formulae to a new power capacitor effectively modeled the performance of the capacitor including the self-resonance peak. Best fit values for external inductance and source resistance were used in this modeling. Inclusion in the discrete model of a series resistance inversely proportional to frequency effectively modeled the flat low-frequency dissipation factor of the commercial polypropylene capacitor