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The optical instrument transformer is a current and voltage measuring system based on Faraday and Pockels effects, whose principles differ from those of conventional industrial transformers. In principle, this transformer is excellent in such aspects as control of electromagnetic induction noise, rationalization of electrical insulation, and extension of dynamic ranges and frequency bands. By making use of such excellent properties, it is possible to achieve higher performance, higher compactness, and higher reliability of instrument transformers. This paper deals with the designing, assembling, and testing results of a prototype of an optical current transformer (CT) and that of a voltage dividing-type voltage transformer (PD). The optical CT and PD were developed to be applicable to 3-phaseenclosed-type 300kV gas-insulated switchgear (GIS) and air-insulated 168kV substation systems. Test results for the newly developed optical CT and PD showed that their basic properties conform with JEC 1201, Japanese standard for electric-power instrument transformers.

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Abstruct-The common path type of differential heterodyne fiber-optic sensing scheme has been developed which uses a polarization maintaining fiber as either a sensor or an optical lead and a dual-frequency dual-polarization laser beam. The sensing schemes are applied to the measurements of temperature, strain, force, pressure, rotation rate (gyro), magnetic and electric fields, and thin film thickness. The sensing scheme and main performances for each measurand are described. High precision and high stability as well as good linearity for each measurand are demonstrated.

This paper describes the development and applications of a fiber-optic electric current sensing technique with the stable properties and compact, simple, and flexible structure of the sensing device. The special characteristics of the sensors were achieved by use of the special low birefringence fiber as the Faraday-effect sensing element and were also achieved with creation of sensing schemes which matched with the features of the fiber. Making use of the excellent features of the sensing technique, various current monitoring devices and systems were developed and applied practically for the control and maintenance in the electric power facility. In this paper, the design and performance of the sensing devices are introduced first. After that, examples of the application systems practically applied are also introduced, including fault section/point location systems for power transmission cable lines.

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