In order to find the synergy of double-break vacuum circuit breakers (VCBs), we conducted a synthetic test including different vacuum gaps, different type electrodes, and different grading capacitors. The double-break VCBs are composed of Axial Magnetic Field (AMF) and Transverse Magnetic Field (TMF) contact VCBs, which can constitute four combinations. The optimal combination of AMF and TMF type electrodes was obtained by comparing with the breaking capacity and voltage distribution of the four combinations. The breaking capacity of double-break VCB with AMF and TMF type electrodes in series while the AMF interrupter is on the lower side is largest because the voltage distribution is the most even which is caused by the different equivalent capacitances of different interrupters. The optimal matching vacuum gaps of the best combination were obtained by a synthetic test of different vacuum gaps, which may make the grading capacitors of double-break VCBs small, even obsolete. The combination of maximum breaking capacity was series AMF type interrupters with suitable grading capacitors of 500-2000 pF. The experimental results provide the best combination and matching control mode for VCBs with double-break.

The grading capacitor is a conventional method to guarantee the uniform voltage distribution (VD) of double-break vacuum circuit breakers (VCBs). However, the main shield voltage unevenness problem of each vacuum interrupter drew little attention in previous study. This article focused on the voltage sharing of the main shield and designed a novel grading capacitor pattern. A dynamic charge compensation (DCC) theory was proposed, which was derived from the novel grading capacitor pattern. Subsequently, an equivalent circuit model, which contained the influence of the DCC, was established for dynamic VD of double-break VCBs. The tests were performed in a synthetic test circuit, and VDs with different grading capacitors patterns were compared, respectively. The results showed that the novel grading capacitor pattern could not only improve the main shield VD but also enhance the effect of balancing the VD ratio between interrupters. The images of cathode spots extinction process correlated the initial condition with postarc sheath growth process. With 83-pF grading capacitors, the compensation effect could reach nearly 50%. Theoretical analysis and test results show the feasibility of the novel grading capacitors pattern, which provides a candidate to put VCBs toward transmission voltage.

In order to reveal the mechanism of the residual magnetic field in vacuum interrupters (VIs), the vacuum arcs and the postarc characteristic with external AMF at current zero are investigated. The magnetic field of the 10-kV/20-kA VIs is analyzed. And then, the phase shift and the residual AMF are obtained. The test platform is established in the synthetic test circuit. The pulsed AMF is applied at current zero with the pulsewidth of 4 ms, and the magnitude can be adjusted from 0 to 200 mT. The transparency VIs with external AMF at current zero is observed by the high-speed CMOS camera to analyse the vacuum arcs development. The postarc current and transient recovery voltage are measured by the postarc current measuring equipment and the voltage divider so that the postarc characteristic such as postarc current and postarc charge can be obtained. The influence of the pulsed AMF at current zero on the vacuum arc development and postarc characteristic is gained and the mechanism of the AMF at current zero is analyzed, which can be useful to special AMF contact design for different applications.