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Summary form only given. Optical fiber current sensors for high-voltage electric power substations have been under investigation in the 1980s and 1990s. So far, however, a number of technical shortcomings such as unacceptable sensitivity to temperature and vibration as well as concerns about their long-term reliability have contributed to prevent extended commercial use. We report a sensor which, we believe, meets all important performance requirements. Two configurations of the sensor have been investigated. In the Sagnac configuration the magnetic field of the current induces a differential optical phase shift, proportional to the current. In the reflection configuration left and right circular polarizations are co-propagating in the coil and are reflected at the coil end.