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From the viewpoint of mitigating global warming by S[F.sub.6] gas, this paper discusses breakdown (BD) characteristics of different electronegative gas mixtures with [N.sub.2]O gas as S[F.sub.6] gas substitutes for quasi-uniform electric field under lightning impulse voltage applications. Experimental results revealed the positive synergism in breakdown strength of binary [N.sub.2].O/C[O.sub.2] and ternary [N.sub.2].O/C[O.sub.2]/[O.sub.2] gas mixtures, respectively. Furthermore, [N.sub.2] gas as a retardant gas was also mixed with the electronegative gas mixtures in order to reduce the electron energy into the effective levels of electron attachment ability by the electronegative gas mixtures. As the result, ternary [N.sub.2].O/ C[O.sub.2] / [N.sub.2] and quaternary [N.sub.2].O / C[O.sub.2] / [O.sub.2] / [N.sub.2] gas mixtures could exhibit the significant synergistic effect in breakdown strength. The optimum mixture rate of quaternary [N.sub.2].O /C[O.sub.2]/[O.sub.2]/[N.sub.2] gas mixtures was consistent with that estimated by assuming the independent contribution of component gases to the improvement of impulse BD characteristics. Index Terms--GIS, impulse breakdown, [N.sub.2].O gas, S[F.sub.6] substitutes.

This paper describes the fundamental insulation characteristics of environmentally friendly gases; dry air, N2 and [N.sub.2] [O.sub.2] mixed gas. Conventional gas insulated switchgear (GIS) generally uses [SF.sub.6] as against over 72.5 kV class. We have proposed GIS with a vacuum circuit breaker against from 72.5 kV class to 170 kV class as [SF.sub.6]-free GIS. Because the insulation gas of this type of [SF.sub.6]-free GIS has the hardly unnecessary current interception performance, the optimal insulation gas can be selected based on fundamental insulation performance. From the standpoints of insulation performance and economical efficiency, we selected compressed dry air as the optimal insulation gas for this type of [SF.sub.6]-free GIS. However, the dielectric strength of dry air is approximately one-third that of [SF.sub.6] gas. Therefore, to achieve roughly the same size as conventional GIS, some strategies must be employed to enhance insulation performance. This paper investigates the influence of gas pressure and a gas/solid hybrid insulation structure. The insulation performance of the gas/solid hybrid insulation structure using an insulation coating was found to be better than that of a barrier. Moreover, the dielectric strength of particles adhering to a spacer under the compressed dry air was about 1.5 times higher than that under [N.sub.2]. Thus, the high insulation reliability of the gas/solid hybrid structure was high against particles was confirmed. In view of these investigative findings, this type of [SF.sub.6]-free 72.5 kV GIS which was designed and manufactured, was confirmed to comply with the IEC standard. Index Terms--Air insulation, disconnecting switches, electric breakdown, gas insulated switchgear, vacuum circuit breakers.

The thermal runaway properties of a conduction-cooled Bi2212 High Temperature Superconducting (HTS) coil are examined. Findings reveal the effectiveness of monitoring the coil temperature and current for the diagnosis of the thermal runaway under the compensating operation for load fluctuations.

The electrical insulation reliability of solid spacers in Gas Insulated Switchgears (GISs) is an important issue to achieve a safe operation of such equipment. Among different phenomena, charge accumulation represents the most important matter that can degrade the overall performance of these insulation systems. For this respect, this paper discusses the contribution of partial discharge (PD) activity by ac voltage application to charge accumulation in the small gap at the electrode/epoxy interface as one of the weakest points in GIS solid spacers. The partial discharge inception voltages for non-accumulated charge case (PDIV0) and after exposing to PD activity (PDIVn) are measured among different gap lengths, simulating delamination at the electrode/epoxy interface. The PD activity is generated using applied voltage with 1.2 x PDIV0 for all gap lengths examined in this study (50~500 µm). In these measurements, PDIV increased with increasing the number of PD pulses as a result of accumulated charges. The accumulated surface charge density is estimated using the boundary equations and is compared for the different gap lengths. The accumulated charge density was larger for the smaller gap lengths. Comparing PD parameters with accumulated charge density enabled us to identify that the number of negative and positive PD pulses is the main parameter that corresponds to charge accumulation process. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the thermal runaway characteristics of a BSCCO HTS single pancake coil conduction-cooled with a 4 K-GM cryo-cooler system. We also evaluate the static and dynamic characteristics of the HTS coil by measuring the temporal evolution of the temperature and the voltage for steady current and the typical current patterns of the load fluctuation compensation at different ambient temperatures T0 in the range of 20-50 K. Moreover, we experimentally discuss the criterion for monitoring the conduction-cooled HTS SMES system during compensating operation for load fluctuations. [ABSTRACT FROM AUTHOR]

We have been developing Superconducting Fault Current Limiting Transformer (SFCLT) as a superconducting transformer with current limiting function. As the Step-5 of the SFCLT project for the up-graded ratings of current and voltage, in this paper, we focused on the up-grading of current by parallel-connected YBCO coated conductors. Based on the asymmetric configuration of coated conductors, different parallel connections were tested and evaluated in terms of critical current level and current limiting characteristics under large ac current at 77 K in liquid nitrogen. [ABSTRACT FROM AUTHOR]

From the viewpoint of mitigating global warming by SF6 gas, this paper discusses breakdown (BD) characteristics of different electronegative gas mixtures with N2O gas as SF6 gas substitutes for quasi-uniform electric field under lightning impulse voltage applications. Experimental results revealed the positive synergism in breakdown strength of binary N2O/CO2 and ternary N2O/CO2/O2 gas mixtures, respectively. Furthermore, N2 gas as a retardant gas was also mixed with the electronegative gas mixtures in order to reduce the electron energy into the effective levels of electron attachment ability by the electronegative gas mixtures. As the result, ternary N2O/CO2/N2 and quaternary N2O/CO2/O2/N2 gas mixtures could exhibit the significant synergistic effect in breakdown strength. The optimum mixture rate of quaternary N2O/CO2/O2/N2 gas mixtures was consistent with that estimated by assuming the independent contribution of component gases to the improvement of impulse BD characteristics. [ABSTRACT FROM AUTHOR]

This paper describes the fundamental insulation characteristics of environmentally friendly gases; dry air, N2 and N2 O2 mixed gas. Conventional gas insulated switchgear (GIS) generally uses SF6 as against over 72.5 kV class. We have proposed GIS with a vacuum circuit breaker against from 72.5 kV class to 170 kV class as SF6-free GIS. Because the insulation gas of this type of SF6-free GIS has the hardly unnecessary current interception performance, the optimal insulation gas can be selected based on fundamental insulation performance. From the standpoints of insulation performance and economical efficiency, we selected compressed dry air as the optimal insulation gas for this type of SF6-free GIS. However, the dielectric strength of dry air is approximately one-third that of SF6 gas. Therefore, to achieve roughly the same size as conventional GIS, some strategies must be employed to enhance insulation performance. This paper investigates the influence of gas pressure and a gas/solid hybrid insulation structure. The insulation performance of the gas/solid hybrid insulation structure using an insulation coating was found to be better than that of a barrier. Moreover, the dielectric strength of particles adhering to a spacer under the compressed dry air was about 1.5 times higher than that under N2. Thus, the high insulation reliability of the gas/solid hybrid structure was high against particles was confirmed. In view of these investigative findings, this type of SF6-free 72.5 kV GIS which was designed and manufactured, was confirmed to comply with the IEC standard. [ABSTRACT FROM AUTHOR]

SF6 gas has excellent dielectric strength and interruption performance. For these reasons, it has been widely used for gas-insulated switchgear (GIS). However, use of SF6 gas has become regulated under agreements set at the 1997 COP3. Presently, development of a gas circuit breaker (GCB) using CO2 gas and development of a high-voltage vacuum circuit breaker (VCB) are being pursued. GIS consists of disconnectors (DS), earthing switches (ES), and buses (BUS) in addition to GCB. Since the interruption performance is not an important requirement for DS, ES, and BUS, use of a gas with high dielectric strength is better than use of a gas with good interruption performance. Air and N2 are not greenhouse gases, and their dielectric strengths are higher than those of other SF6 alternative gases, but only about one-third of the dielectric strength of SF6 gas. This paper deals with a suitable insulation gas which has no greenhouse effect as an SF6 alternative gas. The N2/O2 mixed gas was investigated by changing the ratio of O2. Moreover, the effect of an insulation coating was investigated and compared with the dielectric strength of SF6/N2 mixed gas. The dielectric strength of air under the coating condition was equal to that of 10% SF6/N2 mixed gas. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(3): 9–17, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20348 [ABSTRACT FROM AUTHOR]