Patent ID: 7158898

Claim:
A method of calculating effective power relating to a capacitor, comprising the steps of: obtaining a equilibrium temperature of the capacitor for each of a plurality of sine waves, and substituting a first capacitance and a first dielectric tangent of the capacitor for each of a plurality of equilibrium temperatures into the following equation: Pe = tan ⁢ ⁢ δ 1 + ( tan ⁢ ⁢ δ ) 2 · π ⁢ fCb 2 Pe: effective power tan δ: dielectric tangent C: capacitance f: frequency b: sine-wave amplitude in order to obtain a first effective power for each of the equilibrium temperatures; obtaining a voltage value and a frequency from the waveform of a periodic voltage applied to both ends of the capacitor, and setting a plurality of provisional temperatures, and obtaining a second capacitance and a second dielectric tangent for each of the provisional temperatures, and substituting the second capacitance and the second dielectric tangent into the following equation: Pe = tan ⁢ ⁢ δ 1 + ( tan ⁢ ⁢ δ ) 2 · π ⁢ fC ( a 2 + b 2 ) Pe: effective power tan δ: dielectric tangent C: capacitance f: frequency a: cosine-wave amplitude b: sine-wave amplitude in order to obtain second effective power corresponding to the periodic voltage for each of the provisional temperatures; determining a temperature at which the first effective power is approximately equal to the second effective power as a target equilibrium temperature of the capacitor; and determining the first and second effective powers corresponding to the target equilibrium temperature as a target effective power corresponding to the periodic voltage.