A fiber-optic current sensor based on a differentiating Sagnac interferometer

A fiber-optic current sensor (FOGS) based on a differentiating Sagnac interferometer (DSI) is demonstrated to measure high-voltage ac current in electric power systems from 5 A to 3200 A. A transducer consisting of Rogowski coil and piezoelectric cylinder (PZT) is used as the phase modulator, which is placed in the high-voltage side. The DSI is placed in the ground side. A simple analytical expression for the sensor has been derived, and the input-output performance and the temperature dependence of FOGS have been experimentally investigated. The simple sensor geometry gives high accuracy and sensitivity, wide dynamic range, and immunity from slow-variance temperature and other environmental fluctuations.