Abstract

The vacuum switch with the cup-typed axial magnetic field contacts, of which the advantages are such as lower arc voltage, less contact erosion, large breaking capacity, smaller size, and so on, is widely applied in the AC power system. To utilize it for the DC interruption, this paper analyzed the characteristics of vacuum interrupter with cup-typed axial magnetic field contacts during the DC fault current forced to zero process by using finite element method. The conclusions were obtained as follows: 1) the magnetic flux density in the axial direction (Bz) presents consistency along with the longitudinal direction in gap space, and the largest phase delay in the center of transverse section. 2) After the starting of the arc burning, Bz has an approximately 1-1.5 ms phase delay at first, later is growing proportionally to the fault current increasing rate. 3) As increasing the frequency of the superposed reversed current, the phase delay of Bz is intensified, which result in the value of Bz around the first current zero being very close to the one at the moment of beginning commutation, and it is adverse to the breaking current.

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