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Our research has investigated the use of C[F.sub.3]I, which has lower Global Warming Potential (GWP), as a substitute gas for [SF.sub.6]. The use of pure C[F.sub.3]I in gas insulated switchgear (GIS) and gas circuit breakers (GCB) is difficult because liquid C[F.sub.3]I has a high boiling point. We have therefore mixed C[F.sub.3]I with C[O.sub.2] or [N.sub.2]. By investigating the decomposed gas after a current interruption, we have shown that the iodine density from C[F.sub.3]I-C[O.sub.2](30%-70%) is about 1/3 of that of pure C[F.sub.3]I. in addition, no fluorine was detected from the gas mixture. Our investigation of the breakdown voltage characteristics has shown that the dielectric strength of C[F.sub.3]I-C[O.sub.2] (30%-70%) is about 0.75 to 0.80 times that of [SF.sub.6]. In Breaker Terminal Fault (BTF) and Short Line Fault (SLF) interruption, C[F.sub.3]I-C[O.sub.2] is superior to C[F.sub.3][I-[N.sub.2]. Because of the high boiling point of C[F.sub.3]I, the proportion of C[F.sub.3]I should be small. In BTF interruption, the performance approximates to that of pure C[F.sub.3]I when the proportion of C[F.sub.3]I exceeds 30%. Similarly, the SLF interruption performance approximates to that of pure C[F.sub.3]I when the proportion of C[F.sub.3]I exceeds 20%. Index Terms--C[F.sub.3]I, Breaker Terminal Fault (BTF), substitute gas for S[F.sub.6].

A model superconducting fault current limiter (SFCL) with high-speed communication switch is discussed. Findings reveal that the model SFCL is able to decrease the temperature rise for adapting the high-speed circuit breaker and is also able to reduce the heat load of the superconductor.

We studied the interruption performance of [CF.sub.3]I gas because its environmental effect is smaller than that of [SF.sub.6] gas with a model arc-extinguishing chamber. First, we measured the arc time constant and arc power loss coefficient using Mayr's equation. Comparing [CF.sub.3]I with other gases, the arc time constants are [SF.sub.6] < [CF.sub.3]I < [CO.sub.2] < [H.sub.2] < Air < [N.sub.2]. The arc power loss coefficient is [H.sub.2] > [SF.sub.6] > [CO.sub.2] > Air > [N.sub.2] > [CF.sub.3]I. Next, we evaluated the Short Line Fault (SLF) interruption capability by measuring the di/dtdv/dt characteristic. Consequently, the SLF interruption performance of pure [CF.sub.3]I was about 0.9 times that of [SF.sub.6]. However, [CF.sub.3]I application to gas insulated switchgear (GIS) and gas circuit breakers (GCB) is difficult because the liquefying temperature of the gas is high. Therefore, we adopted a countermeasure to obtain a lower liquefying temperature mixing [CF.sub.3]I with [CO.sub.2]. The result showed that the SLF interruption performance of the mixture approximated that of pure [CF.sub.3]I when the ratio of [CF.sub.3]I exceeds 20%. Index Terms--[CF.sub.3]I, short line fault (SLF), substitute gas for [SF.sub.6].

In Japan during the 20th century, developments of high voltage transmission and distribution apparatus advanced tremendously and circuit breakers were the center of these developments. And as a result, 1100 kV [SF.sub.6] gas insulated switchgear (GIS) for ac transmission systems and also 500 kV dc GIS for dc transmission systems have become available. Vacuum circuit breakers (VCBs) have also been actively developed and a 168 kV two break VCB and 100 kA VCB are already available. This paper describes these developments and future trends in technology. Index Terms--Future trends, high voltage, Japan, [SF.sub.6] circuit breaker, vacuum circuit breaker.

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.

The interrupting chamber for 550kV 1-break gas circuit breaker (GCB) was developed. To cope with voltages and interrupting capacities of nearly double per break compared with 2-break GCBs, the shape of the interrupting chamber was optimized, and an interrupting chamber scheme using arc energy was employed. Small-current interrupting performance was improved by selecting a nozzle shape with pressure fluctuations due to a supersonic flow at the downstream side of the nozzle and dielectric recovery characteristics taken into account. By employing an interrupting chamber scheme utilizing arc energy, the opening speed is increased by minimizing the reaction due to pressure rises in the puffer chamber in small-current interruptions or the pressure is sharply raised due to the effect of arc energy in large-current interruptions. The nozzle shape is also optimized for a large-current interruption by improving the efficiency of treating hot gas.