Toshinori Kimura

Discharge characteristics for various discharge patterns under negative lightning impulse voltage in vacuum

In order to develop higher voltage vacuum interrupters (VIs), electrical insulation performances in vacuum should be improved. The discharge in VI has various and complex patterns, such as breakdown in vacuum gap and surface flashover on a solid insulator. In this paper, we investigated three discharge patterns: the discharge in vacuum gap, the discharge in vacuum gap via shield, and the surface flashover on solid insulator, respectively. By measuring shield potential and insulator surface potential, we analyzed the discharge characteristics for various patterns, and clarified the relevant discharge development process. We found that the breakdown development process in vacuum gap depends on the gap length and the surface flashover development process on a solid insulator depends on the applied voltage and surface distance.

Discharge characteristics of composite insulation system with floating electrode and solid insulator in vacuum

For the development of vacuum interrupters for their higher voltage application in power transmission systems, it is necessary to clarify the discharge characteristics of composite insulation systems with a shield (floating electrode) and a solid insulator in vacuum. In this paper, we focus on the composite discharge patterns via the shield and the solid insulator. For cathode-shield-insulator-anode (c-s-i-a) and cathode-insulator-shield-anode (c-i-s-a) electrode configurations, the discharge can be classified into two independent processes: breakdown in vacuum gap and surface flashover on the solid insulator. Furthermore, we have found that the breakdown development time increases with the increase in the gap length and the surface flashover development time depends on the voltage peak after flashover inception, which are consistent with discharge development characteristics for individual gap breakdown and surface flashover, respectively. These results are significant to understanding and discriminating the composite discharge patterns and discharge path in vacuum interrupters.

Observation of tungsten particles in vacuum arcs by laser induced fluorescence

The authors have clarified the relation between the decay of tungsten ion density in the vicinity of current zero and vacuum arc mode by using LIF method and a high speed video camera in tungsten vacuum arc of 60 Hz sinusoidal current with the peak value of 3.3, 6.7 and 9.8 kA. The tungsten ion density before current zero decreased as the current decreased. In the case of 6.7 kA, the transition to the anode spot mode occurred and an arc column was observed. The density near the anode before current zero was higher than near the cathode and the density near the anode was about 10 times as high as the case of 3.3 kA which was diffuse mode. In the case of 9.8 kA, the density near the anode was not significantly different from 6.7 kA. But the density near the cathode was higher than near the anode and the eruption from the cathode was observed by a high speed video camera. They concluded the arc at 9.8 kA was the intense arc mode. And the density at current zero was higher than the other case and tungsten ion was observed until about 30 /spl mu/s after current zero.

Discharge pattern discrimination for composite insulation system in vacuum interrupter

For the development of vacuum interrupters (VI) for their higher voltage application in power transmission systems, the investigation and clarification of discharge characteristics in a composite insulation system with a shield (floating) electrode and a solid insulator in vacuum are necessary. The discharge phenomena and patterns at internal insulation failures in VI are complex and various. In this paper, based on the discharge development characteristics, we proposed a novel discrimination method of the discharge pattern in vacuum. In addition, we executed iterative verification tests of the proposed discrimination method by using a model which simulates the insulation system of VI. The results revealed that 50 discharge events with 5 patterns were discriminated in the total 54 tests. Therefore, the discrimination success rate reached 93%, and the effectiveness of the proposed discrimination method for discharge patterns in VI was confirmed.