In this paper

a great deal of theoretical analyses on the calculation of unbalance protection for high voltage three-phase AC filter capacitor are carried out and it is pointed that: Unbalance protection calculation for high voltage AC filter capacitor is more complicated than that for shunt compensation capacitor

not only in the calculation of fundamental component

but also in the calculation of harmonic component.The calculation of fundamental component is similar to that of shunt compensation capacitor.The calculation of harmonic component is selectively analyzed.Three-phase circuit model for shunt calculation of harmonic current of harmonic source in the system and asymmetrical capacitance circuit of three-phase is given

and

on the basis of such model

the harmonic current and voltage of the capacitor as well as various formulas for calculating unbalance protection harmonic component are derivated.The total unbalance current or voltage should be equal to the square root of sum of square of its respective component.In this paper

the theoretical base and applicable calculation formula for unbalance protection calculation of filter capacitor are provided.