Temperature-Insensitive Sagnac-Type Optical Current Transformer

We estimated the influence of polarization crosstalk in a Sagnac-type optical current transformer (OCT) against sensor sensitivity, and confirmed that temperature dependence of Faraday effect is canceled out by controlling the extinction ratio of transmission fiber with temperature change. Based on the evaluation, we developed a temperature compensation element (TCE) consisting of metal-coated PM fiber. Its extinction ratio varies with temperature because of the difference between the linear expansions of metal and fiber. The ratio error of OCT using this TCE in the temperature range from -40 to 80 °C was within 0.1%, and satisfied the required accuracy for IEC 60044-8 class 0.2S for ac applications and IEC 61869-14 class 0.2 for dc applications.