This article proposes a general physics-based model for identifying the parasitic capacitance in medium-voltage (MV) filter inductors, which can provide analytical calculations without using empirical equations and is not restricted by the geometrical structures of inductors. The elementary capacitances of the MV inductor are identified, then the equivalent capacitances between the two terminals of the inductor are derived under different voltage potential on the core. Further, a three-terminal equivalent circuit, instead of the conventional two-terminal equivalent circuit, is proposed by using the derived capacitances. Thus, the parasitic equivalent capacitance between the terminals and the core are explicitly quantified. Experimental measurements for parasitic capacitances show a good agreement with the theoretical calculations.