Kiyoshi Okumura

Optical Voltage and Current Measuring System for Electric Power Systems

Recently, optical voltage and current measuring methods based on a principle different from that of the existing apparatus have been developed. As the most promising method among them, a voltage measuring method which uses an electrooptic effect called the Pockels effect and a current measuring method which uses a magnetooptic effect called the Faraday effect have been proposed. The authors have developed an optical voltage measuring system based on the electrooptic effect in bismuth germanium oxide Bi4Ge3O12 and a current measuring system based on the magnetooptic effect of borosilicate crown glass for the purpose of utilization in electric power systems. As a result of the development, high accurate voltage and current measuring systems such as non linearity error less than ±0.4% and temperature stability less than ±1.0% were obtained. Furthermore, short-circuit current was measured with the current measuring system, and an accuracy within 0 to -4% in the range of 30 kApeak to 150 kApeak was obtained. When the measuring systems were mounted on the model of 70 kV class gas insulated switchgears, it was verified that the measuring systems had satisfactory linearity and temperature stability.

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.