Temperature and vibration insensitive fiber-optic current sensor

A robust interferometric fiber-optic current sensor with inherent temperature compensation of the Faraday effect is presented. Sensor configurations based on Sagnac and polarization-rotated reflection interferometers are considered. The sensing fiber is residing and thermally annealed in a coiled capillary of fused silica. The capillary is embedded in silicone within a ring-shaped housing. It is theoretically and experimentally shown that the temperature dependence of the birefringent fiber-optic phase retarders of the interferometers can be employed to balance the temperature dependence of the Faraday effect (0.7/spl times/10/sup -4///spl deg/C). Insensitivity of the sensor to temperature within 0.2% is demonstrated between -35/spl deg/C and 85/spl deg/C. The influence of the phase retarders on the linearity of the sensor is also addressed. Furthermore, the sensitivity to vibration of the two configurations at frequencies up to 500 Hz and accelerations up to 10 g is compared. High immunity of the reflective sensor to mechanical perturbations is verified.

I. Introduction

Current sensors employing the Faraday effect in a coil of optical fiber are very attractive for metering, control, and protection in high-voltage substations. Advantages include the inherent electric separation of the sensor electronics at ground potential from the sensing fiber coil at high voltage as well as the small size and weight. As a result, the sensors can be integrated into existing high-voltage equipment such as circuit breakers and bushings. This eliminates the need for bulky stand-alone devices for current measurement. Furthermore, the output signals, in contrast to the power outputs of conventional inductive current transformers, are compatible with modern digital control and protection systems. For a review of optical current sensing techniques, see [1].