Fiber-optic current and voltage sensors for electric power transmission systems

Optical current and voltage sensors have become attractive alternatives to conventional instrument transformers in high voltage electric power transmission systems. The optical sensors offer important benefits such as small size and weight, enhanced performance, and constitute an important part of the transition to digital substations. The sensors must comply with stringent accuracy and reliability requirements. Commonly, substation applications demand accuracy to within +/- 0.2% over outdoor temperature ranges. Other aspects are insensitivity to shock and vibration and stray fields as well as life times in excess of 30 years. We review the technology of the sensors and present particular measures that were necessary to achieve the required performance. This includes the exploration of different sensing fiber types, inherent temperature compensation, accelerated life tests, and, in case of voltage sensors, adequate high voltage proof insulation and packaging. We discuss the integration of a current sensor into a circuit breaker and show results from a corresponding field test.