Taiki Donen

Motion observation of particles between electrodes and subsequent breakdown phenomena in vacuum

The influence of particles on breakdown and pre-breakdown phenomena in vacuum was experimentally investigated. The Cu sphere particles were injected artificially between 10-mm gap plane electrodes made of Cu and the movement of particles was measured by a high speed camera under AC and DC voltage application. The correlation among the motion of particles, the field emission current and the breakdown phenomena was examined. Under the application of high voltage between the electrodes, most particles bounced up and down between the electrodes. However, some particles attached to the electrode after the collision to the electrode and detached from the electrode after the reversal of voltage polarity. It is natural to say that those attached particles were covered with insulating oxide layer. In most cases the speed of attached particles exceeded that of bounced particles and the impact speed of attached particles to the opposite electrode exceeded 50m/s with 10-mm gap and 100-kVp applied voltage. These high speed particles detached from the electrode at various voltage phase, even at around 0-phase. Discharges induced by collision of these attached particles were also observed.

Investigation of correlation between vacuum breakdown phenomena and field emission current during shunt capacitor switching

In the case of interrupting capacitive loads, the most challenging problem for vacuum interrupters is to withstand recovery voltage during opening operation. In addition, the field enhancement factor of vacuum contacts is assumed to be high due to the damage of contacts caused by making the inrush current. In this paper, simulated shunt capacitor switching tests are carried out and the field emission current across the contact gap is measured to research the influence of the inrush current on the breakdown phenomena during opening operation. All breakdowns occur before the gap spacing reaches the maximum value and it is determined that there is a correlation between the electric field breakdown and the field emission current measured before the breakdowns. Furthermore, the found correlation is independent of the amplitude of the inrush current. The electric field breakdown is nearly invariant under the condition that the measured field emission current is constant regardless of the inrush current. However, the field emission current tends to be high in the presence of a large inrush current. The difference in the expected field emission current is believed to affect the electric field breakdown.

Plastic deformation of electrode at collision with particles in vacuum gap

The discharge process in vacuum is usually classified into two types, micro particle type and field emission type. The influence of particles has been experimentally investigated using a high speed camera. However, few studies have reported the quantitative analysis on the particle type discharge. To understand the micro particle type discharge better, the collision phenomena between a sphere particle and an electrode were investigated in this paper. The contacting time and the plastic deformation length of the electrode at a collision were analyzed by solving the equation of motion with changing the initial velocity and the diameter of a particle. It was calculated that the contacting time varied from dozens of nanoseconds to hundreds of nanoseconds and plastic deformation length varied from 0.1 to several micron meters when particle diameter was 10 to 50 micron meters and the initial velocity was 1 to 100 meters per second. The heat generation related to particle collision was calculated and its results suggest that protrusion on a particle can induce vacuum discharge, but kinetic energy loss may not. These results will provide a basic view for understanding the micro particle type discharge in vacuum.

Optical measurement for particle production in vacuum interrupter

Vacuum interrupters have some merits such as size and maintenance. They have been used widely up to 72 kV, and expected to be used in the higher voltage class. To improve their dielectric performance, it is necessary to clarify vacuum breakdown phenomena. Micro particles are not negligible especially concerning vacuum interrupters used in the high voltage class. Therefore, the authors have developed optical measuring system for particle behavior in vacuum. In this paper, the authors investigated the causes of particle production and their influence on dielectric performance. The authors focused on two different causes of particle production as follows: (a) contact melting during current interruption, (b) mechanical damage of contacts during closing operation. Concerning “(a) contact melting during current interruption”, it turned out that particles generated during the current interruption are able to be significantly suppressed by current conditioning. Concerning “(b) mechanical damage of contacts during closing operation”, it turned out that some particles were generated by the high-velocity closing operation. The breakdown voltage just after the mechanical damage was about 70% of the conditioning voltage. Closing velocity would have some influence on particle production.

Temperature measurement and arc rotation observation of spiral-type contact

In this paper, the authors report the relation between the arc rotation and the temperature of contact surface. The interruption tests were performed with the vacuum chamber equipped with spiral-type contacts. The rotation of vacuum arc was observed with high speed cameras from two different directions. The temperature of the contact surface was estimated from emission intensity measured by high speed camera with the infrared band-pass filter. Local surface overheating occurs with slow-speed arc rotation, whereas surface temperature rises homogeneously with high-speed arc rotation. In addition, differences of arc behavior certainly effects on the interrupting performance.

The impact of capacitive switching condition on vacuum breakdown phenomena

In the case of switching capacitive loads, breakdown electric field of vacuum interrupter tends to decrease because contacts of vacuum interrupter are damaged by large making current. In this paper, the authors investigated the decreased breakdown electric field from the following two viewpoints. First, the relation between breakdown electric field and condition of opening operation was investigated. The breakdown electric field was invariant regardless of whether mechanical impact of opening operation was applied. On the other hand, the breakdown electric field tended to increase when opening operation was carried out with long arc time. These results indicate that the field emission mainly determine the breakdown phenomena. Secondly, the relation between breakdown electric field and making current was investigated. On the whole, the larger the amplitude of making current became, the lower breakdown electric field tended to be. However, the breakdown electric field was exceptionally high when the generation time of making current arc was long. This is because arc of making current diffused rapidly.