In this paper

the principle of the protection of the capacitor with internal fuse is introduced briefly according to the internal structure of the capacitor

if the internal components of the capacitor breakdown

the series internal fuse in fuse

the capacitance will change accordingly

and will lead to the changes of the unbalanced current ultimately.In this paper

two kinds of typical protection on double differential current bridges of large capacity capacitor bank are calculated and analyzed

a simple formula is derived

and according to actual operating data

the practical applications are verified.