Influencing Factors Analysis on the Detector Output Signal of Fiber Optic Current Transformer with Sine Modulation

Abstract To investigate the measurement failure mechanism of fiber-optic current transformer (FOCT) with sine modulation, the detector output of FOCT is established and the expression of the output signal is given to explore its influencing factors. The demodulation method of FOCT is studied and the results show that the optical path parameters, modulation signal and measured current affect the second harmonic component in detector output, and may further cause FOCT measurement failure when the second harmonic component is low. Calculation and simulation are carried out to analyze the influence of each factor on detector output signal and the second harmonic component. The results show that the rise of optical path parameters and modulation signal will enlarge the output range of the detector, and the two factors are positively correlated with the second harmonic component, which may decrease as the measured current rises. Tests of the theoretical analysis were verified by experiments in Huai'an and Taizhou UHV Converter Stations.