Characteristics and Influencing Factors of the Postarc Current in Vacuum DC Interruption

The postarc current (PAC) is an important parameter, which can indicate the interrupting capacity of breakers. According to the amplitude of the PAC, the appearance of the arc before current zero and the quantity of residual metal vapor particles in the electrode distance after current zero can be studied qualitatively. In order to investigate the characteristics of PAC in direct current (dc) interruption, a high-speed hybrid actuator was designed, and the forced current zero method was used to carry out a series of dc interrupting experiments in the synthetic test circuit. Also, the equipment for measuring the PAC was established to investigate the factors influencing on the PAC, including the amplitude of rated breaking current, electrode distance, and commutation frequency. The experimental results indicated that PAC presented to be instable in a certain range, due to the different contact structures, arcing positions, and so on. To some extent, the instability of PAC reflects the sheath growth process after the current zero. In addition, the amplitude of PAC changes with the variation of electrode distances. For the same distances, PAC keeps stable in a certain range. When the rated breaking current is less than 800 A, PAC increases with a high growth rate. However, the one increases with a low growth rate when the rated breaking current varies within 800-2000A. For different commutation frequencies, PAC has a significant growth with the increase of the commutation frequency. It is for the reason that more residual metal vapor particles exist in the electrode distance after current zero when the commutation frequency is higher, which goes against to dc interruption.