Highly accurate fiber-optic DC current sensor for the electro-winning 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 electro-winning 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 magneto-optic 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 re-enforced epoxy, which can be installed without opening the current-carrying bus bars. Subsequent re-calibration is not necessary. The sensor achieves accuracy within ± 0.1% over a wide range of currents and temperatures.