Abstract
The objective of this work is to determine the relationship between the vacuum arc transient behaviors and voltage characteristics in low-current DC interruption under a rotating transverse magnetic field (TMF). An external rotating TMF was generated by two pairs of Helmholtz coils, set at right angles. The phase angle of alternating currents in the two Helmholtz coils was shifted by 90°. The rotating frequency was 230 Hz, with a peak flux density of 32 mT. The contact material was CuCr25 (25% Cr), with a diameter of 18 mm. The DC vacuum arc appearance was recorded by using a high-speed CCD video camera. The experimental results indicate that the voltage characteristics were closely related to the DC vacuum arc transient behaviors. In low-current DC interruption under a rotating TMF, vacuum arcs experienced two main stages of evolution, a constriction and motion stage and an unstable stage. The increase in the arc voltage, caused by the unstable state of the cathode spot group located at the edge of the contacts and the stretched state of the DC vacuum arc column, was the key for DC vacuum successful interruption under the rotating TMF. Moreover, the interruption characteristics of the DC vacuum arc were quite sensitive to the contact separation length and the rotating TMF flux density. The duration of the total interruption process decreased with the increase in the rotating TMF flux density, which mainly affected the duration of the constriction and motion stage in the DC vacuum interruption.
Highlights
DC switchgears, as key equipment for the safety and protection of DC electric systems, are expected to meet the rapid growth and various demands for wind power generation, solar microgrids, electric vehicles, and so on.1 The large growth of the capacity and voltage of DC electric systems presents new challenges for the development of DC interruption technology
The duration of the total interruption process decreased with the increase in the rotating transverse magnetic field (TMF) flux density, which mainly affected the duration of the constriction and motion stage in the DC vacuum interruption
The function of the rotating TMF was the same as the singlepole TMF generated by Helmholtz coils11,16 and the different TMFs generated by permanent magnets,12,15 in the DC vacuum interruption
Summary
DC switchgears, as key equipment for the safety and protection of DC electric systems, are expected to meet the rapid growth and various demands for wind power generation, solar microgrids, electric vehicles, and so on. The large growth of the capacity and voltage of DC electric systems presents new challenges for the development of DC interruption technology. The large growth of the capacity and voltage of DC electric systems presents new challenges for the development of DC interruption technology. To promote the application of VCBs in DC systems, much attention has been paid to the DC vacuum interruption technology.. Due to the relatively low voltage value of vacuum arcs, it is difficult to interrupt a DC current in vacuum directly.. The general method is to create an artificial current zero by connecting an external circuit. The necessary external circuit will result in a complex interrupting circuit.. The necessary external circuit will result in a complex interrupting circuit.3,6–8 Another proposed method is to increase the arc voltage of the DC vacuum arc. When the arc voltage increases higher than the circuit voltage, it forcibly reduces the DC arc current to zero directly.
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