Masao Hosokawa

Synthetic Testing and Interrupting Phenomena Under Short Line Fault Conditions

This paper is a contribution to work on the problems of synthetic testing under short line fault conditions. The various factors which must be taken into account when assessing validity are discussed, and the experimental evidences to support the validity of the parallel current injection method are described. The paper also deals with the severest current range in short line fault conditions for different types of circuit breakers.

Dielectric Characteristics of Gas Insulated Bushings in Air Under Dry and Wet Conditions

Dielectric characteristics of an EHV gas insulated bushing to be used for SF6 gas insulated switchgears are reported. From observation of the lightning impulse flashover under dry conditions with an image converter camera, the flashover process of the bushing in air is clarified. It was found that the electric field strength of the porcelain surface on the lower part of the bushing had a large influence on insulation performance. The tilt angle of the bushing was changed as a result of studying the switching impulse dielectric characteristics of the bushing under wet conditions; and the water stream on the exterior surface of the bushing was seen to have a large influence. It was demonstrated that dividing the water flow along the porcelain surface made an improvement in insulation performance.

Dielectric Performance of Improved Gas Insulated Bushing for UHV Gis

This paper describes a improved gas insulated bushing for ultra high voltage (UHV) SF6 gas insulated switchgear (GIS) which contains a simple capacitor core inside a porcelain housing. The effects of arrangement and capacitance of the capacitor core on the voltage distribution along the external porcelain surface were analyzed, and a 2/3 scale model of a prototype UHV gas insulated bushing (6.7m porcelain housing) was developed. Characteristics tests of the voltage distribution and dielectric withstand voltage indicated that the voltage distribution was greatly improved and the dielectric withstand voltage of the switching impulse under wet conditions was enhanced about 30% compared with a conventional gas insulated bushing.

Breaking Ability and Interrupting Phenomena of a Circuit Breaker Equipped with a Parallel Resistor or Capacitor

This paper discusses the breaking ability of an air blast circuit breaker (ABB) or SF6 gas circuit breaker (GCB), and the interrupting phenomena around current zero in the case where a resistor or capacitor is connected in parallel with its interrupter to improve the breaking ability. It has been clarified that the use of a parallel resistor for ABB, and that of a parallel capacitor for GCB are the most effective methods to improve the breaking abilities; the parallel resistor not only serves to reduce the rate of rise of the transient recovery voltage (rrrV), but also shifts the current from the interrupter to itself around the current zero, thus reducing the stress for interruption. The improvement of the breaking ability is achieved by reducing the initial average rrrV between zero and 1 microseconds (inherent value), when the parallel capacitor is used with the GCB.