Kunio Yokokura

Physical and theoretical aspects of a new vacuum arc control technology-self arc diffusion by electrode: SADE

Our new vacuum arc control technology SADE doubles the high current interruption capability of our conventional axial magnetic field technology. First, we describe the vacuum arc motion behavior recorded by a high speed charge-coupled device video camera. This arc behavior is closely related to axial magnetic field intensity. In particular, it depends on the profile of the externally generated axial magnetic field. The anode spot is likely to move to the highest magnetic field intensity. Second, we describe analytical results for concentration of vacuum arc at the anode side contact surface. This analysis implies the possibility of an ideal magnetic field profile and intensity for vacuum arc control. Finally, we describe experimental results for vacuum arc control compared with the physical and theoretical results mentioned above, and we show a practical electrode configuration for vacuum interrupters and its application in a high current interruption experiment.

Recent technical developments in high-voltage and high-power vacuum circuit breakers

Explanations are given regarding recent technical topics in the development of vacuum circuit breakers. The area-effect concept is introduced to aid in insulation designs of vacuum interrupters. By using Cu-Cr prepared through a special method, the voltage performance of vacuum interrupters has been remarkably improved. Through the development of axial magnetic field electrodes, large-current interruption has been made possible. The design concept for determining contact radii has been established. A computer simulation method for generating switching overvoltage is described, thereby indicating the possibility of realizing large-current interrupting vacuum interrupters with low switching overvoltages. >

The effect of contact material on temperature and melting of anode surface in the vacuum interrupter

We have investigated the relationship between the contact material and the anode surface condition subjected high current arc in a vacuum by measuring and calculating the temperature of the anode surface. We tested CuCr contacts with Cr contents varying from 12.5 to 75 wt% under an axial magnetic field. The two-color pyrometer was used to measure the anode surface temperature around the contact center region. The high sensitivity CCD camera with the bandpass filter was used to measure the relative temperature distribution immediately after current interruption. We calculated the temperature of the anode surface considering melting and evaporation. It is shown that the Cr contents of the CuCr contact influence the temperature, the anode surface melting and the interruption ability. With increase in Cr content of the CuCr contact, the temperature of the anode surface and the melting duration after the current interruption increased. The maximum melting depth of the anode surface decreased with increase in Cr content. The measurement results also showed that the interruption ability improved with decrease in Cr content, and the anode surface temperature of the CuCr contact was 2000-2050 K at the interruption limit.

Capacitor switching capability of vacuum interrupter with CuW contact material

The authors carried out shunt capacitor switching tests on 24 kV model vacuum interrupters with contact materials CuW and CuCr. The restriking probability of the contact material CuW is lower than that of CuCr. The contact material CuW is also an excellent candidate for shunt capacitor switching except for its high current interruption ability. The restriking probability of a 24 kV, 25 kA vacuum interrupter with contact material CuW is calculated as 10/sup -5/, which is practically zero. >

The basic investigation of the high-speed VCB and its application for the DC power system

The fundamental phenomena and applications of the high-speed vacuum circuit breakers, which forced the fault current to zero, in a DC power system for railways were investigated experimentally and through simulations. The results showed the necessary performance of high-speed VCBs for DC power systems. The test circuit breaker consisted of a vacuum interrupter, a high frequency current source and a high-speed driving mechanism. The vacuum interrupter, which had the axial magnetic field electrode, was tested. The arcing period of high-speed vacuum circuit breakers is much shorter than that of conventional circuit breakers. The arc behavior between the contacts immediately after the contact separation was observed by a high-speed video camera. The effect of varying the current waveform just before current interruption was investigated and its effect on the interruption ability was quantified. The results demonstrate the interruption ability and the arc behavior of the high-speed vacuum circuit breaker. These results were applied to high-speed circuit breakers for DC power systems of railways.

Possibility of high current interruption of vacuum interrupter with low surge contact material: improved Ag-WC

High-current interruption experiments were carried out on low-surge contact material Ag-WC set in axial magnetic field electrodes. The most influential factors on high-current interruption are the contact material, the axial magnetic field, and the initial opening speed. Though the interruption ability of conventional contact material was limited up to 20 kA, the ability of the improved material rose up to 40 kA in the test using the laboratory model vacuum circuit breaker. >

Fundamental investigation and application of high-speed VCB for DC power system of railway

The fundamental phenomena of the high-speed vacuum circuit breaker, which forced the fault current to zero, for the DC power system were investigated by the experiments. The interruption characteristics of the circuit breaker, which was consisted from a vacuum interrupter, a high frequency current source and a high-speed driving mechanism, were estimated experimentally. The arcing period of the high-speed vacuum circuit breaker is much shorter than that of conventional circuit breaker. The arc behavior of the test electrodes immediately after the electrode separation was observed by a high-speed video camera. The relation between the current waveform just before current zero and the interruption ability by varying the high frequency current source was investigated. The results demonstrate the interruption characteristics and the arc behaviors of the high-speed vacuum circuit breaker. And the high-speed vacuum circuit breakers were applied for DC1500V and DC750V power systems of railway.

Dielectric breakdown probabilities for uniform field gap in vacuum

To investigate the reliability of the insulation of equipment having vacuum incorporated as an insulation medium, a study was carried out to clarify breakdown probability distributions in the vacuum gap. Experiments were carried out to investigate the effects of test methods, electrode area, and electrode materials on the breakdown probability distributions of uniform-field gaps. The test results show that the breakdown probability distribution of the vacuum gap can be represented by a Weibull distribution using a location parameter, which shows the voltage that permits a zero breakdown probability. When aiming for highly reliable vacuum insulation equipment, an important factor is insulation design with the location parameter just mentioned taken into account. The location parameter depends on electrode area. This is probably because the existence probability of factors as weakpoints for breakdowns such as micro-protrusions and micro-particles depends on the electrode area.

The characteristics of the vacuum arc and the interruption ability on the high-speed vacuum circuit breaker

A high-speed vacuum circuit breaker, which forced a fault current to zero, has been investigated. The characteristics of the arc behavior and the interruption ability were investigated experimentally. Two types of electrode, an axial magnetic field electrode and a disk-shaped electrode, were tested. The results demonstrate the characteristics of the arc behavior and the interruption ability of the high-speed vacuum circuit breaker.

The Arc Behavior and the Interruption Ability of the Transversal Magnetic Field Electrode in the Vacuum Interrupter

Vacuum interrupters have been widely used for power distribution systems with the development of vacuum arc control technology by magnetic field. There are two major electrode types: transversal magnetic field electrode and axial magnetic field (AMF) electrode. In the former, the vacuum arc column is rotated by the magnetic force generated by the transversal magnetic field, which is radial direction to the electrode, and the current flowing in the arc. In the latter, the vacuum arc is diffused and stabilized by the axial magnetic field, which is parallel to the arc current. Transversal magnetic field electrodes have been researched experimentally. To increase interruption ability by preventing local heating of the electrode, the relationship between the arc behavior and the interruption ability was researched. A high speed video camcorder was used to observe the arc behavior. The interruption ability of the transversal magnetic field electrode was evaluated using Weil test circuit. The arc observations and interruption test results indicate the relationship between the arc behavior, the magnetic field, and the interruption ability