Masafumi Yashima

Mechanism and effect of DC charge accumulation on SF/sub 6/ gas insulated spacers

Mechanism and effect of DC charge accumulation on the surface of a solid insulating support (spacer) have been studied in compressed SF/sub 6/ gas using various cylindrical model spacers. The distribution of surface charged is closely related to the normal component (gas side) E/sub n/ of electric field on the spacer surface. The ,maximum charge density can be estimated from the condition of E/sub n/=0. When voltage is applied in a polarity opposite to prestressed DC, surface charge increases the maximum field strength in the arrangement, resulting in the reduction of the insulating ability. It is possible to estimate the lowest flashover voltage due to surface charges only from numerical fields calculations. An anticharging spacer shaped along electric lines of force is proposed and studied. >

Measurement of Accumulated Charge on Dielectric Surfaces with an Electrostatic Probe

ABSTRACT This paper discusses the measurement method of the accumulated charge (density σ) on the surface of solid dielectrics (specimens) such as DCGIS spacers. The relation between σ and the probe response has been discussed for various arrangements with uniform or nonuniform charge distributions. The charge in the surrounding area has a very large effect on the probe response especially for thick specimens. True surface charge distribution can be obtained by the multi-point measurement method with the aid of a numerical field calculation. The effectiveness of the method has been demonstrated experimentally for a model specimen.

Lightning Impulse Breakdown Characteristics of High-Pressure N2 as an Alternative Insulation Gas to SF6

Recently, SF6 has been identified as a greenhouse gas with a long atmospheric lifetime1. Therefore, recycling guidelines for SF6 in electrical power equipment have been discussed, and the reduction of the release of SF6 to the atmosphere has progressed2. In addition, many researchers have investigated alternative insulation gases to SF6 3-5. High-pressure N2 gas is one of the proposed alternative gases that have no need of SF6. Pure N2 has a lower withstand voltage level than SF6, but has the advantage of being not only environmentally friendly, but also low in cost and safe. The breakdown characteristics of compressed N2 have already been discussed as part of the basic study on gas discharge in the 1930s6. However, most data on the electrical breakdown of compressed N2 were obtained under limited experimental conditions (small electrode scale or kinds of applied voltage waveform), and are not sufficient to estimate the insulation performance.

Estimation of Cross-Sectional Size of Gas-Insulated Apparatus Using Hybrid Insulation System with SF6 Substitute

SF6 has been identified as a greenhouse gas with a long atmospheric lifetime1. Therefore, recycling guidelines for SF6 in electric power apparatus have been studied, and the reduction in the amount of SF6 released into the atmosphere has progressed2. In the long term, it is preferable to reduce the amount of SF6 used. Therefore, it may be important to discuss the possibility of using environmentally friendly gases as an alternative insulation gas for practical gas-insulated apparatus.

Basic properties of hybrid gas-insulated transmission lines (H-GIL)

The recent trend in electric power consumption shows a steady increase and concentration in large cities and industrial districts. This indicates a strong need for a long-distance and enclosed-type power transmission line with large capacity and high reliability. A hybrid gas-insulated transmission line (H-GIL), which has the combined features of an XLPE cable and a conventional gas-insulated transmission line (GIL), has the potential to be applicable to such use. n nIn the present work, we analyze the required dimension and the current capacity of H-GIL on the basis of insulation and thermal design for various parameters determining the structure. We also report an experimental study on flashover characteristics for a simple electrode model of H-GIL. The results show that the H-GIL can be realized with almost the same sheath diameter and current capacity as a conventional GIL. The experiment has also clarified that the insulation reliability of the H-GIL is much higher than that of a GIL. These properties show that the H-GIL has enough feasibility applicable as a long-distance and reliable transmission line with large capacity especially in urban areas.