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We have investigated the performance of silicone oil as an insulating medium with the aim of developing environmentally-friendly, flame-retardant electric power equipment. We have studied the streaming electrification characteristics of silicone oil during flow, with regard to its use in the cooling of electric power equipment, at temperatures from 30 to 130 [degrees]C. The effects of the insulator material on the charge density in the oil and on the accumulated charge density in the insulator were investigated. We use four kinds of insulators, including aramid paper, in these experiments. The silicone oil was negatively charged by streaming electrification, in contrast to conventional mineral oil. The magnitude of the accumulated charge density in the insulator was influenced by the kind of insulator. It was also found that the charge density in the silicone oil and the accumulated charge density in the insulator changed with increasing temperature. Moreover, we investigated the effect of the kinematic viscosity on the streaming electrification by performing experiments using oils with kinematic viscosities of 20 cSt and 50 eSt. We have considered the optimum combinations of silicone oil and insulator material. Index Terms--Silicone oil, streaming electrification, charge density, electric power equipment.

Since the majority of vacuum circuit breakers in use are of the single-break variety, there have been few studies of double-break vacuum circuit breakers. This report describes our investigations of the interruption characteristics of the double-break vacuum circuit breaker. In this investigation, the post arc current and recovery voltage distribution ratio were measured in order to clarify the relationship between them. The results show that a bias of the voltage distribution ratio occurs when the post arc current value becomes imbalanced. In addition, the measurements of the post arc current for circuit breakers with spiral contacts are very scattered as compared with those with axial magnetic field contacts. Normally, the double-break vacuum circuit breaker consists of two contacts of the same type. However, when two spiral contacts are used, the scattering of post arc current causes a current imbalance. As a result, a bias of the voltage distribution ratio may occur. It appears to be preferable to use double-break vacuum circuit breakers with axial magnetic field contacts. Index Terms--Double-Break, grading capacitors, post arc current, vacuum circuit breakers, vacuum interrupters, voltage distribution ratio.

The lightning impulse breakdown characteristics of various combinations of insulation material in silicone oil for use in electric power apparatus were investigated, with the aim of reducing the amount of oil required and thus the cost. Breakdown characteristics were investigated in a system in which an insulating filler was mixed with silicone oil. Tests were conducted on a sphere-plane electrode in a vertical arrangement and a sphere-sphere electrode in a horizontal arrangement. The relation between the breakdown strength and the electric field strength was clarified. Breakdown characteristics were also investigated in a system in which an insulator with low relative permittivity was inserted between a filler with high relative permittivity and the high-voltage electrode. Based on the findings, optimum conditions for the application of silicone oil to electric power equipment are proposed. Index Terms--Silicone oil, electric power equipment, triple junction, breakdown characteristics, combined insulation, Nomex[R].

We present a study of the performance of silicone oil as an environmentally friendly and flame retardant insulating medium for electric power equipment. We have investigated the streaming electrification characteristics for flowing silicone oil for cooling of electric power equipment. As the initial step, the electric charge density accumulated in silicone oil and on the surface of the insulator is investigated simultaneously. We have used 5 types of insulating material for the experiment, including aramid paper. Silicone oil becomes negatively charged by streaming electrification, in contrast to conventional mineral oil, and the magnitude of the electric charge density on the insulating material is influenced by the kind of insulating material. As the second step, the streaming electrification characteristics of silicone oil were further examined using an insulator for which the work function is known. Based on these results, streaming electrification for various kinds of insulator and silicone oil is evaluated with respect to the work function. We consider the optimum combination of silicone oil and insulating material. Index Terms--Electric power equipment, silicone oil, streaming electrification, anticipated series of streaming electrification, work function.

To realize the high-voltage vacuum circuit breaker, we investigated the voltage-distribution ratio after current interruption at the double-break vacuum circuit breaker. We used the spiral CuCr (20%) electrodes and the axial magnetic-field CuCr (50%) electrodes as the experimental electrodes. At the double-break vacuum circuit breaker, where two vacuum interruptions that had the same and different characteristics of the electrode structure and contact materials were connected in series, there was a bias in the voltage-distribution ratio of each vacuum interrupter after current interruption. This seems to be because there was difference in the postarc current that passed through each vacuum interrupter after current interruption. Index Terms--AC circuit breakers, capacitance, interrupts, voltage breakdown.

Non-Sustained Disruptive Discharge (NSDD) sometimes occurs when the voltage is applied for a certain time between vacuum gaps after the current is interrupted. However the mechanism of NSDD has not yet been clarified. We conducted a study to clarify this phenomenon using the contact materials CuCr, CuW, and AgWC. We applied a voltage (20[kV]-30[kV]) of ac 50[Hz] after current interruption (1[kArms]-8[kArms]), and checked the generating frequency of NSDD. After the current interruption test, we measured the contact surface roughness and field emission current. The result showed that surface roughness and field emission current are not related to this phenomenon and also that CuCr (melt) showed the best performance in all tests. Index Terms--Non-sustained disruptive discharge (NSDD), metallic particle.

This paper describes the surface breakdown characteristics of silicone oil which has the possibility of application to innovative switchgears and transformers as an insulating medium. At the first step, we have experimentally studied the impulse breakdown characteristics of the configuration with a triple-junction where a solid insulator is in contact with the electrode. The test configuration consists of solid material (Nomex[R] or pressboard) and liquid insulation oil (silicone or mineral oil). We have discussed the experimental results based on the maximal electric field at the triple-junction. As the second step, we have studied the configuration which may improve the surface breakdown characteristics by lowering the electric field on the insulator surface. Index Terms--Surface breakdown, Electric power apparatus, silicone oil, triple junction, discharge inception voltage.

Insulation recovery characteristics after current interruption for a vacuum interrupter were investigated. We used spiral and axial magnetic field electrodes for comparison of the electrode structure, while CuBi and CuCr were also used for comparison of the contact material. This paper describes how the axial magnetic field electrode and CuCr (50%) performed best in our experimental data. In addition, we discussed reasons for the variation in characteristics between electrodes. Index Terms--Vacuum insulation recovery, copper chromium, copper bismuth, vacuum interrupters, electric breakdown.

To clarify the instability phenomena of a low-current vacuum arc, we observe the phenomena by changing the parallel circuit parameters. We measure instability-initiation current, chopping current, arc voltage, reignition voltage peak, and the transient recovery voltage by using copper, copper chromium, copper tungsten, and silver tungsten carbide electrodes. We find that the chopping current, reignition voltage peak, and transient recovery voltage depend on parallel circuit parameters, but the instability-initiation current and arc voltage do not depend on them. We also find that the instability phenomena depend primarily on the cathode material. Index Terms--Chopping phenomena, electrode material, low-current instability, reignition voltage peak, vacuum arc.

In order to investigate an [SF.sub.6] circuit breaker arc under nonequilibrium conditions, a complete self-consistent kinetic model has been set up. The number of chemical reactions equals 87, involving 35 different species of the [SF.sub.6] dissociation products and their ionized and excited states. The collisional-radiative (CR) model determines the plasma composition and the temperature simultaneously in one point. Additionally, the Boltzmann equation will be solved to determine the electron impact parameters. Results for a free-recovering [SF.sub.6] arc as well as the [SF.sub.6] plasma exposed to electric fields will be presented. Index Terms - Boltzmann analysis, circuit breaker arc, [SF.sub.6] plasma.

New methods have been developed for investigating vacuum arcs applied to the improvements of vacuum interrupter electrodes. Electrode surface temperature measurements reveal the anode surface melting condition at the current interruption and its influence on interruption capability, and a digital image processing technology gives us a clear understanding of the arcing phenomenon. Measurements and test results have shown the advantages of axial magnetic field electrodes in increasing the interruption capability of vacuum interrupters. It is confirmed that axial magnetic field electrodes are superior to other types of electrodes, and we believe that these new investigation methods promote the optimization of the electrode structure and the realization of higher voltage and current rating vacuum interrupters. Index Terms - Arc control, vacuum arc, vacuum interrupter.

Superconducting current limiters (SFCLs) can limit short-circuit fault current and provide sufficient time for DC circuit breakers (DCCBs) to isolate faults. An SF6 passive resonance DCCB combined with a superconducting current-limiting module and a DC interruption module is proposed due to the high current interruption properties and the low on-state loss. However, experimental investigations of SF6 passive resonance DCCBs combined with SFCLs using DC source are currently lacking. The objective of this paper is to obtain the interruption characteristics and modeling design methods of the proposed SF6 passive resonance DCCB. This paper designs a 10 kV SF6 passive resonance DCCB and tests the DCCB in a 10 kV/10 kA circuit. Quenching resistance and arc models are established based on experimental results. Experimental results show that the superconducting current-limiting module responds fast at 0.3 ms and limits the DC fault current of 10 kA to a peak of 816 A. Then the DC interruption module interrupts the limited current successfully. Besides, there is no overvoltage afterward in all the tests because the superconducting current-limiting module absorbs much of the energy during the interruption. The proposed DCCB would be an effective method for interrupting short-circuit faults in high voltage DC systems. [ABSTRACT FROM AUTHOR]