A fiber optic current sensor suitable for electric power system is introduced.In order to improve the measurement accuracy of FOCT

a closed-loop signal detection method based on DSP+FPGA is presented.Some main error sources and corresponding suppression methods are analyzed.According to IEC 60044-8

various accuracy tests of FOCT are designed.The experimental results indicate that the ratio errors of FOCT prototype for the input AC and DC current are all less than±0.2% within -40～+60℃.At room temperature

AC current metering accuracy of prototype exceeds 0.1%

and phase delay is less than 129.6′.Measurement accuracy of FOCT for harmonic current within 51 orders is less than 0.5%.The designed FOCT prototype reaches 0.2 class in IEC60044-8 in metering accuracy.