This paper describes development of optical fiber current sensors along with some of their applications. Optical fiber current sensors based on the Faraday effect have long been expected to replace conventional current transformers as compact and high performance current sensors. Yet because they require complex means for achieving stable characteristics, this type of sensor has never come into widespread practical use. To solve these problems we developed a special sensor fiber made from flint glass and created sensor systems whose sensing method ideally matches the characteristics of the fiber. These sensors we developed are immune to environmental effects such as vibration and temperature changes. They are also compact and flexible, and attach easily around conductors. This paper also introduces some typical applications of these sensors including cable current measurement using a portable type sensor, a fault section locating system for power transmission lines using these sensors, and sensor applications to protective relay systems as verified in field tests.
