Evaluation of a Fiber-Optic Current Sensor for On-site Calibrations

Fiber-optic current sensor (FOCS) technology offers intrinsic galvanic isolation, a wide linearity range, immunity to electromagnetic interference, and non-invasive measurement, making it a strong candidate for applications in on-site calibration. However, its use as a traceable reference in metrological applications remains limited so far. Laboratory calibration and cross-institutional comparisons are essential steps toward establishing the reliability and traceability of FOCS in real-world conditions. This paper provides an overview of the FOCS operating principle and evaluates the key performance of a new FOCS sensor tested in two National Metrology Institutes (NMIs), including accuracy, stability, linearity, and temperature dependence. It furthermore describes the on-site measurement campaign using the FOCS for efficiency measurement in a medium-voltage substation. The test results reveal that FOCS can meet the performance requirements under practical conditions and demonstrate excellent repeatability and traceability for on-site calibration in operational environments: the linearity is better than $0.1 \%$ over the 2.4 kA current range, with temperature effects less than $0.2 \%$ from -10 to 60 degrees Celsius. This work contributes to understanding the metrological characteristics of FOCS and supports their broader adoption in on-site calibration.