Optical current transformer for gas insulated switchgear using silica optical fiber

The high accuracy optical current transformer (optical CT) for gas insulated switchgear (GIS) using a silica optical fiber has been developed. The linear birefringence was reduced by twisting the newly developed double coated optical fiber. The current of up to 8000 A was measured within electric noise error of 3.8 Arms and a sensitivity change of /spl plusmn/0.4% was observed over the temperature range from -20 to 90/spl deg/C. This change corresponds to the temperature dependence of the Verdet constant of silica. When the vibrating acceleration of 8G was applied by the gas circuit breaker motion, no signals were distinguished from the background noise level of 3.8 Arms. The long term test was carried out and the accuracy of the measurements was kept to within /spl plusmn/0.15% during 8 hours. This is the first practical optical CT to satisfy all requirements for GIS.