A High-Performance Hybrid Current Transformer Based on a Fast Variable Optical Attenuator

We present a novel hybrid electro-optic current transformer based on a fast variable optical attenuator (FVOA) with the features of ultra-low power consumption and polarization insensitivity. An optic-electro feedback loop with a PID control algorithm is designed to compensate the nonlinearity of the FVOA. In addition, the impacts of the power drift of the optical source and variance of fiber loss have been investigated and eliminated. The transformer is built with a verified power consumption of 0.85 mW. Experiments were made in which the linearity, the robustness, the accuracy and the temperature stability of the transformer were tested. The results show that the ratio errors and the phase errors are below 0.07% and 5 min, respectively, when the primary current increased from 25 to 600 A. In addition, the maximum error drifts of 0.17% and 2.8 min were recorded over the -20 to 80°C range.