Motoharu Shiiki

Dielectric Performance of CO2 Gas Compared with N2 Gas

SF6 gas is widely used in electric power apparatus such as gas insulated switchgears (GIS) and gas circuit breakers (GCB) due to its excellent dielectric and arc-quenching performance. However, SF6 gas has recently been recognized as a greenhouse gas and it was decided to reduce its emissions at COP3 at Kyoto in 1997. Thus, surveys on the amount of emissions and efforts to reduce emissions have been started all over the world. Simultaneously, studies on alternative gases to SF6 gas have increased. In fact, studies on alternative gases, the purpose of which was to find a gas that had better performance than SF6 gas, had been carried out previously. However, the purpose of recent studies is to reduce environmental impact.

Forces affecting metallic particle motion in GIS

The bounce height of a metallic particle in Gas Insulated Switchgear (GIS) is one of the key factors which affect GIS reliability. Simulation of particle motion can evaluate bounce height if the relevant forces acting on the particle are taken into account. This paper presents an approach to simulating particle trajectories including dipolar force and drag force from SF6 viscosity. The influence of various forces is evaluated through the comparison between the simulation results and particle trajectories determined from high speed camera observation of particle motion.

Electrical properties of composite material containing microvaristor and tetrapod ZnO

In recent years, Gas Insulated Switchgear (GIS) is becoming compact which implies a relatively high electric field in the enclosure. In the result, its compactness can make metallic particles move easily. To suppress the movement of particles in the tank of GIS, the nonlinear resistive coating has been developed [1]. The coating contains the microvaristor. However, the sedimentation of microvaristor often occurs in the microvaristor filled composite. The effective way to prevent sedimentation of microvaristors was found [2]. In the method, adding the special shaped semi-conductive zinc oxide (tetrapod ZnO) is of current interest. In this paper, the role of the second particle on the conduction was discussed.

Approximate formula of electrostatic force on spheroidal particle between coaxial electrodes

An existence of an electrostatic force which draws the particle in the direction of increasing field was indicated by FEM analysis. An approximate formula of the electrostatic force was derived analytically and compared with the results of FEM analysis. This force is sufficiently large to be relevant to particle motion in gas insulated switchgear.

Electrical properties of composites with microvaristors and several secondary fillers

Reduced dimensions of Gas Insulated Switchgear (GIS) implies a relatively high electric field in the enclosure. To suppress particle movement in the GIS tank, a nonlinear resistive coating has been developed that contains microvaristor fillers. The effect of putting several secondary fillers is important to understand the mechanism of electrical properties of the composites. In this paper, the effects to the electrical properties of adding microvaristor / secondary filler content in the microvaristor filled composites were investigated. Besides, inner structure measurement, calculation, and simulation of the composite were conducted.