基于等效电路的电容器内熔丝设计

Design of Capacitor Internal Fuse Based on Equivalent Circuit

目前,国产的高压电容器内部大都装有保护熔丝,并与每个并联单元串联,一旦其中某个元件损坏,利用瞬时流过的短路电流熔断保护熔丝,可将故障元件切除。因此,电容器内熔丝应按照其熔断特性来选择。本文首先讨论了在恒定电流下,为保证电容器内熔丝可靠熔断必须使其自身发热产生的能量大于熔丝材料的汽化能量,并得出此边界能量与熔丝尺寸的计算公式。其次,根据电容器内部单元结构的等效电路图,推导出故障单元处内熔丝的总发热量。然后,根据通流能力选择熔丝截面积,进而利用边界熔断能量和总发热量,计算熔丝长度。根据本文提出的方式设计内熔丝尺寸,得到的结果与实际使用中的相近,说明本文所提供的方式可以较为方便地对内熔丝尺寸进行准确的计算。

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-cir-cuit 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 mate- rial so to assure reliable fusing of capacitor internal fuse at constant current is discussed, and calcu- lation 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 u-nit structure of capacitor. After that, sectional area of fuse is selected as per current-carrying capaci-ty 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.