E. Kaneko

Post Arc Current in Vacuum Interrupters

Detailed measurements of post arc current in a vacuum were made and the results were compared with theory. This comparative study was particularly characterized by conducting post arc current measurements following high arc current (36 kA rms maximum). Three kinds of electrode materials and two types of electrodes were used to elucidate effects of the electrode materials and the types on post arc current. Shield current was also measured to clarify the characteristics of the ion current. The characteristics of post arc current are explained by referring to those results.

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. >

Basic Characteristics of Vacuum Arcs Subjected to a Magnetic Field Parallel to Their Positive Columns

As vacuum arcs subjected to a magnetic field parallel to their positive column (an axial magnetic field) spread uniformly over all the electrodes and burn in the interelectrode region, arc voltages of these arcs are low and quiescent. When the magnetic field strength decreases, however, the arc voltage develops a large noise component and electrode melting occurs. Experiments were conducted to investigate the condition of these transition phenomena. As a result of these experiments, it was found that these two phenomena do not always occur simultaneously and that a new explanation for the mechanism of anode spot formation should be considered.

History of vacuum circuit breakers and recent developments in Japan

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.

Influence of electrode area on the conditioning effect in vacuum

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. >

Insulation characteristics of vacuum interrupter for a new 72/84 kV C-GIS

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, the authors describe the basic characteristics on surface insulation and the area effect on surface insulation and their application to an new 72/84 kV CGIS.

An investigation into major factors in shunt capacitor switching performances by vacuum circuit breakers with copper-chromium contacts

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. The authors found a microparticle-induced breakdown phenomena that could explain the mechanism of long delayed restrikes that is occasionally observed in vacuum circuit breakers. >

The Investigation of Copper-Chromium Contacts in Vacuum Interrpters Subjected to an Axial Magnetic Field

The characteristics of a vacuum arc between CuCr contacts under an axial magnetic field have been investigated. Test samples were made of CuCr contacts, and the arcing voltage was measured. The arcing voltage of the CuCr contacts under an axial magnetic field is lower than that of pure copper contacts by 10-20 V. From the measurement of the post-arc current and interruption test results, it was found that the arc concentrates and a part of the electrode melts at a rather low current, but that the electrode melting does not affect the interrupting capability. Also, the insulation characteristics were measured. With respect to voltage conditioning, high-current conditioning improved the breakdown voltage by 50 percent for a 20-mm gap and by 100 percent for a 3-mm gap. These test results show that CuCr contacts, used with axial magnetic fields, are promising for use in high-voltage and high-power vacuum interrupters.

Experimental characterization of arc instabilities and their effect on current chopping in low-surge vacuum interrupters

In low-current vacuum arcs, short (< 500 ns) peaks in arc voltage (instabilities), with a height of up to ten times the normal arc voltage, are abundantly present. The instabilities are thought to be caused by ion starvation near the anode. A number of parameters of these instabilities, occurring in vacuum interrupters with AgWC (low-surge) and CuCr (conventional) contact material, have been analyzed statistically in a practical ac circuit. A striking difference in median rate of rise (2.8 kV/ps for CuCr versus 0.63 kV/ps for AgWC) and height (134 V for CuCr versus 54 V for AgWC) is found. It is made plausible that these parameters reflect important switching Characteristics such as recovery (peak rate of rise) and current chopping level (peak height). Also, the dependence of the parameters on momentary arc current and contact distance is studied and explained qual- itatively. It is concluded that current chopping takes place as a result of a high-frequency arc current oscillation with an increasing amplitude. This oscillation is excited periodically at the current minima by a series of instabilities in a self-enhancing way. In an analysis of the interaction between arc and circuit, the well-known dependence of chopping level on circuit parameters is explained.

Use of Axial Magnetic Fields to Improve High-Current Vacuum Interrupters

When an axial magnetic field is applied to a vacuum arc, the arc tends to be stabilized in its diffuse mode. A minimum arc voltage is found for a certain magnetic field. In this condition, interrupting current is significantly increased, and it is nearly proportional to the diameter of electrodes. About ten years ago, a practical axial magnetic field electrode was developed for vacuum circuit breakers. Since then, through various improvements in its structure, this electrode has been refined for practical application in vacuum circuit breaker interrupters. The application has successfully covered not only medium-voltage circuit breakers, but also high-voltage (84 kV), dc high-voltage, and high-current circuit breakers. In this paper, ten years experience in this area is described.