Voltage and Current Distribution in Metallized Film Cylindrical Capacitors

Voltage and current distribution in metallized film cylindrical capacitors were analyzed in electromagnetic analyses, accounting for both conduction and displacement currents. First, an analytical solution based on an equivalent circuit with distributed infinitesimal parameters for an inductive capacitor with two highly resistive plates was derived. It was compared to COMSOL numerical solutions and was found to be satisfactory. In conformance to published data, the effective capacitance decreases at higher frequencies, and the capacitance drop is more prominent at high metallization resistivity and large capacitance. This capacitance is defined by the energy storage capability and not via input impedance, remaining positive above resonance. Resistivity increase caused by various mechanisms during capacitor aging may lead to additional capacitance loss(CL). The internal inductance of a cylindrical capacitor was derived analytically and compared to field simulations. Next, multisectioned parts with both linear and nonlinear dielectrics were analyzed with COMSOL. The analyses showed that voltage sharing between the capacitor sections may be compromised at DC voltage.