Highly accurate fiber-optic DC current sensor for the electrowinning industry

A fiber-optic current sensor for direct currents up to 500 kA is presented. Applications include current measurement for process control and protection in the electrowinning industry, for example at aluminum smelters. The sensor offers significant advantages with regard to performance and ease of installation compared to state-of-the-art Hall-effect-based current transducers. The sensor exploits the Faraday effect in an optical fiber and measures the path integral of the magnetic field along a closed loop around the current-carrying bus bars. The differential magnetooptic phase shift of left and right circular light waves propagating in the fiber is detected by means of a novel polarization-rotated reflection interferometer. Fiber gyroscope technology is employed for signal detection and processing. The fiber is packaged in a flexible strip of fiber reenforced epoxy, which can be installed without opening the current-carrying bus bars. Subsequent recalibration is not necessary. The sensor achieves accuracy within +/- 0.1% over a wide range of currents and temperatures.