At present

the domestic low-voltage capacitors are equipped with the internal fuse

which are connected to each of the parallel unit series. Once a component of all is damaged

the short-circuit current will flow through the protection fuse. And the fault element is cut off when the protection fuse burn out. Therefore

the capacitor fuse shall be chosen with the fusing characteristics. In this paper

the energy generated by the heat of fuse itself is higher than evaporation energy of fuse material so to assure reliable fusing of capacitor internal fuse at constant current is discussed

and calculation formula of boundry energy and fuse dimension is obtained firstly. Then

total heat of internal fuse at the faulty unit is deduced in accordance with equivalent electric circuit diagram of internal unit structure of capacitor. After that

sectional area of fuse is selected as per current-carrying capacity and fuse length is calculated by the use of boundary fusing energy and total heat. The dimension of internal fuse is designed based on the method proposed in this paper

the obtained result is very close to that in actual application

showing the method provided in this paper can calculate correctly dimension of internal fuse conveniently.