Soichiro Kainaga

Characteristics of discharge progress across barrier in the oil/pressboard composite insulation system under impulse voltage application

It is crucial for reasonable transformer insulation design to understand the characteristics of discharge progress under the application of a standard lightning impulse voltage. This paper deals with the fundamental discharge characteristics of oil/pressboard (PB) composite insulation system. We obtained discharge images using a digital camera equipped with an image intensifier. In this research, we focused on the route of discharge progress along pressboard barrier. Furthermore, we evaluated the discharge velocity as well as the time required for the successive discharge generation across the barrier PB.

Effect of discharge trace formation on creepage discharge characteristics in oil/pressboard composite insulation system under impulse voltage application

Oil-immersed power transformers adopt oil/pressboard (PB) composite insulation system. To downsize the equipment, further understanding about the creepage discharge phenomena is required. In this study, we have investigated the effect of white discharge trace on the creepage discharge in oil/PB composite insulation system. Experimental results show that partial discharge inception voltage (PDIV) became lower after the white trace formation. In addition to this, the formation delay time of the discharge became shorter after the white trace formation. These results can be explained by the gaseous nature of the white trace.

Characteristics of partial discharge in the oil gap separated by pressboard barrier in oil/pressboard composite insulation system

This paper deals with the characteristics of partial discharge in oil/pressboard composite insulation system, which is adopted in oil-immersed power transformer. In the insulating structure of the transformer, large oil gaps are often subdivided by pressboard barriers into small ones. Once partial discharge occurs at the point where the electric field is enhanced and progresses, the electric field distribution may change from the static one. As a result, there are possibilities that partial discharge successively occurs at the oil gap across pressboard barrier, which might be the trigger of breakdown of the apparatus. In this study, the authors experimentally observed the partial discharge generation across the pressboard barrier in an element model and examined the mechanism of the above phenomenon.

Downsizing 550 kV GIS by applying dielectric coating

SF₆ gas has been widely used in high voltage power equipment (HVPE) because of its high insulating and arc-quenching performance. However, the reduction of use of SF₆ is highly required, because SF₆ is a potent greenhouse gas. Thus, the improvement of SF₆ gas insulation system is indispensable in order to further downsize HVPEs with reduced SF₆ usage. In this work, we applied a dielectric coating to 550 kV gas insulated switchgear (GIS) and succeeded in downsizing it and reducing its SF₆ gas content.