Iwao Ohshima

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.

Measurement of Transient Voltages Induced by Disconnect Switch Operation

This paper describes a proposed method of measuring disconnect switch surges and introduces some data derived from applying this method.

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.

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. >

Development of detection and diagnostic techniques for partial discharges in GIS

This paper describes detection and diagnostic techniques for partial discharges in gas insulated substations (GIS). Partial-discharge current waveforms of SF/sub 6/ gas and external noise characteristics of actual substations were investigated, and a measuring system having sensors in GIS and employing frequency range of VHF band was developed. By this system, detecting very small partial discharges of several 10 pC level has become possible. Also, a neural network system, focusing attention as a method for recognizing patterns, was applied for determining causes for partial discharge in GIS, and its applicability has been proved. >

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. >

Types of reignition following high-frequency current zero in vacuum interrupters with two types of contact material

In a special medium-voltage circuit, the mechanism of reignition after high-frequency vacuum arc current zero is investigated experimentally for two types of contact material, i.e., AgWC (low-surge) and CuCr (conventional). For this circuit, the principle of synthetic testing is adopted. Based on a large number of observations, four different types of reignitions can be observed in interrupters with each type of contact material. The types of reignition are classified according to the duration of the currentless pause (5 ns-50 mu s) between interruption and reignition. Analysis of the experiments shows that the breakdown voltage of the gap following high-frequency arcing can both increase and decrease, depending on the high-frequency arc activity. In a tentative analysis, the value of fi/sup 2/dt of prior HF arcing may be considered as a quantitative measure of the influence of the arc on breakdown voltage. >

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. >

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. >