Fiber optical current sensor for quasi-DC currents during high-voltage short-circuit tests

The transition towards sustainable energy systems presents significant challenges for existing power grid infrastructures, especially with the increasing occurrence of quasi-DC currents caused by renewable energy integration, electromobility, and electrified transportation. These quasi-DC currents impose thermal stress on transformers and reduce their service life, necessitating advanced measurement technologies. This study introduces a fiberoptical current sensor (FOCS) based on a modulated Sagnac interferometer, designed to detect and analyze fault currents during short-circuit events in high-voltage substations. The sensor exploits the Faraday effect for highly sensitive and accurate current measurement, overcoming limitations of conventional inductive transducers, such as core saturation and limited bandwidth. Field tests in a 110 kV substation demonstrate the FOCS’s superior performance, including enhanced sensitivity, a stable zero point, and the ability to quantify quasi-DC components. These results highlight the FOCS’s potential for reliable fault current monitoring in modern power grids, addressing critical challenges posed by sustainable energy transitions.