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Vacuum circuit breakers (VCBs) have been developed and widely applied in Japan to meet the requirements of increasing energy consumption and also in national security of various areas. As a result, for example, a 168 kV two break porcelain type and a 100 kA one break VCB have already appeared in the Japanese market and they are currently being exported to world-wide markets. VCBs interrupt currents in vacuum, and this means they do not exhaust dissolved gases which are sometimes harmful to the human body or cause effects on the environment. Therefore, by its nature, the recycling of materials and safety to the human body have been realized, and also no global warming effects would be expected. Energy is extremely essential and important in human daily life, and many types of circuit breakers play important roles in electrical power transmission and distribution systems to maintain the systems reliability and safety by switching the systems under several conditions. Since vacuum circuit breakers possess a lot of advantages such as high current interrupting capabilities, small size, and low cost, they will be used much more in the future, and at this moment, we believe it is very worthy to discuss and consider thoroughly future trends of VCBs. In this paper, the results of the developments in Japan will be reviewed, the reflection of the results will be stated, and the subjects of engineering in the 21st century will be discussed. These will include recycling, safeguards to the human body and the fireless nature of VCBs; and it will be demonstrated that the developmental works of VCBs are being wonderfully explored in Japan now and in the future. Index Terms--History, Japan, Vacuum circuit breakers, Vacuum interrupters.

Experiments were carried out to study the effects of surface polishing and annealing of ceramic specimens on the dielectric breakdown characteristics of their surfaces. It was found that when the samples were annealed at 1000[degrees]C, allowing the residual stresses in their surfaces to decrease, the breakdown voltage rose, whereas with the polished samples, reductions of residual stresses resulted in a slight rise of the breakdown voltage. Prior to dielectric breakdown, a surface glow was observed, due to luminescence from electron bombardment and insulator surface defects. The starting voltage of luminescence rose when residual stresses were reduced. It is suggested that the mechanical strain due to surface defects contributes to dielectric breakdowns on ceramic surfaces.

This paper describes insulation technology for 72/84 kV vacuum interrupter for a new cubicle type gas insulated switchgear (CGIS). The insulation performance has been increased significantly by a multi-gap shield configuration around the ceramic surface, which resulted in a 40% volume reduction of the vacuum interrupter. The CGIS housing the vacuum interrupter also reduced by 40% in volume. In the paper we describe the basic characteristics on surface insulation and the area effect on surface insulation and their application to an new 72/84 kV CGIS.

The aim of this project was to find a correlation between contact gap length and switching behavior of a vacuum circuit breaker. A large number of interruption experiments was executed in a vacuum chamber with butt type contacts made of Cu, CuCr 50/50 and AgWC. The currents to be interrupted varied from 2.5 to 32 kA. The rate of change of current and recovery voltage were kept at a fixed value at current zero. Many re-ignitions of the dielectric type, scattered over a wide range of re-ignition voltages, were observed and only a few of the thermal type. The total amount of energy dissipated in the vacuum chamber appears to be determinative for the type of re-ignition. On Cu severe anode spot melting was found, whereas CuCr and AgWC suffered little anode melting. The wide range of re-ignition voltage values found shows that a straight correlation with the contact gap length can not be defined. At 5 to 10 [[micro]seconds] after current zero a 'second' post arc current did appear.

This paper describes the application of three-dimensional magnetic field analysis, including eddy current effects on the axial magnetic field electrodes. The accuracy of the analysis is verified with both basic and full models of the electrodes. The analytical results were compared with the measured values obtained by the Hall sensor system. The effect of the electrode slit length and the electrical conductivity of the contact on the magnetic flux density and phase difference was analyzed with the full model. The magnetic field in the gap was simulated when the arc ignites between the electrodes. These results demonstrated that the magnetic design of the electrodes can be carried out on an engineering work-station.

Using three types of copper electrodes with different surface areas, experiments were performed to investigate the influence of electrode area on the conditioning effect, which is a characteristic of dielectric breakdown in vacuum gaps. The conditioning process varied with electrode area: the smaller the electrode area, the sooner conditioning ended. Breakdown voltages after completion of conditioning also depended on electrode area: the smaller the electrode area, the higher the breakdown voltage.

Using a scanning electron microscope (SEM) and a laser microscope, we observed micro-flakes and particles on machined Cu-Cr contacts which were considered to be built-up edges due to machining. A large number of microparticles of 5.7 - 8.7 X [10.sup.3] from contact surface of 1 [cm.sup.2], were generated from the machined Cu-Cr contacts during opening and closing operations of normal current. The size of typical microparticles was some tens [[micro]meters] and those larger than 100 [[micro]meters] were occasionally observed. This implies that the surface of machined Cu-Cr contacts must be treated by any means when they are used for vacuum interrupters. Current conditioning is one of the effective surface treatment. Although the surface roughness of the contacts increases through the current conditioning, the improvement of insulating ability is brought by the elimination of micro-flakes and particles and by the formation of fine structure layer preventing partial detachment of the contact material.

The performance of vacuum circuit breakers in switching shunt capacitors depends much more on in-rush current than on interrupting current. This is because when contacts that were fused together by pre-arcs during contact closing are forcibly separated, large protrusions are formed on the contact surface, making it easier for microparticles to be detached from the protrusions. Microparticles are also produced on the entire surface of contacts by mechanical impact or cold weld. Current interruption of a certain magnitude, however, has a conditioning effect because moderate arcs can eliminate such microparticles and lower the protrusions. To clarify the relationship between the behavior of microparticles and the dielectric breakdown, a laser scattering technique was employed. We found a microparticle-induced breakdown phenomena that could explain the mechanism of long delayed restrikes that is occasionally observed in vacuum circuit breakers.

We observed and analyzed the dynamic characteristics of long-stroke stainless steel bellows for a vacuum interrupter when it is extended and contracted at high speeds. Dimensions of bellows tested are as follows: outer diameter 85 mm, inner diameter 62 mm, number of folds 44 and 55. Test conditions : contracted speed : 4 m/s, 2 m/s, extended speed: 2 m/s, 1 m/s. We found that increasing the number of folds on the bellows does not necessarily prolong the life of bellows and it is preferable that the bellows be designed so that the ratio of operation stroke and free length of bellows falls in the range between 0.3 to 0.4.