Research On The Performance Improvement For High Power Triggered Vacuum Switch

With the application of the pulse power technology in military and civilian field, research focusing on pulse power system design is attracting more and more attention. Switch, as the core component of the pulse power technology, is bottleneck that hinders its development. Triggered Vacuum Switch has the advantage of a wide working voltage range, high coulomb property and high trigger accuracy, but its service life is not long in the high current. To solve the problem of trigger failure and the main electrode erosion, the paper carries out a large number of experiments about the life of trigger and main electrode, and we proposed several methods to improve its service life.We built TVS trigger circuit and main circuit to carry out the research which helps to prevent trigger failure. First we performed experiments on disc-type TVS, which has a relatively simple structure and the trigger ring is made from semiconductive material. Insulation resistance of TVS dropped significantly after the experiment, which could easily result in false trigger, and fail to meet the needs of practical application.Therefore, we designed a Multi-rod TVS whose trigger ring is made from high aluminum porcelain. In this structure, the trigger electrode is away from the main gap so it can avoid erosion by discharging arc. The experiment is done using different sizes of TVS, different thickness of the trigger ring and surface of trigger ring with or without glaze respectively. The result showed that under the condition that the gap of trigger ring is 0.5 mm, the trigger voltage is 10 kV and the surface of trigger ring has glaze, the metal deposition of surface decreased, while the service life of the trigger electrode increased.In order to solve the problem of flashover TVS which has decreased insulation resistance with the increase of number of experiments, field-breakdown TVS of T trigger electrode structure is designed. The trigger discharge region is the area between the corner of trigger electrode and the angle of cathode. This structure can increase the degree of electric field distortion, and reduce the trigger voltage. For the proper design of field-breakdown TVS, the plate-plate and needle-plate experiments in vacuum are done. We obtained the changing pattern of breakdown voltage under different gap distances and atmospheric pressures. The analyzed polarity effect of TVS suggests that success rate of the positive electrode is higher than the negative electrode and the breakdown process of field-breakdown TVS is influenced by trigger current.To improve TVS main electrode performance, we conducted life experiments on the disc-type TVS. After a dozen times of high current experiment, when the disc-type TVS were dissected, it has been found that cathode, anode and metal shielding were severely eroded. Research on multi-rod TVS helped us found that main electrode erosion was not severe under rated current, but with the increase of the current, erosion of main electrode becomes apparent. Through quantitative mathematics, we obtained a relationship between TVS current and contacts area.Our research also emphasized on the high power TVS trigger failure and main electrode erosion mechanism. After testing the composition of insulated ring after experiments, we found that as the number of experiments increases, metal deposition of insulated ring surface increases linearly. We used vacuum arc principle to explain the electrode erosion and failure mechanism:at the first step, multi-rod TVS produce arc in rod-plate, and then are formed in the rod-rod. In this structure, arc can be divided into several stage and keeping vacuum arc in parallel connection state. Under different gap distances and cone angles, internal electric field is simulated for field-breakdown and flashover triggered vacuum switch. We acquired the change of the electric field and further understood the conduction mechanism of TVS.We found that trigger performance is influenced by trigger source TVS. Experiment results showed that in indirect trigger circuit, by changing the parameters of pulse transformer and capacitance C1, the trigger current can be increased when the delay time is decreased simultaneously. In freewheeling circuit, the rate of the trigger current rise can reach 150 A/μs, the delay time is 2-4μs. Yet in the trigger circuit, in which the capacitor is in parallel with the second side of the pulse transformer and trigger electrode, the rate of the trigger current rise can reach 20 kA/μs, the delay time is 2μs. In direct trigger circuit without the pulse transformer, the rate of the trigger current rise is greater than 4 kA/us, the delay time shortens to 500 ns, which is the minimum. The delay time can be shortened obviously by changing the trigger circuit, when the trigger stability is also be improved.