Error characteristic analysis of fiber optic current transformer with sine modulation

Abstract

The optoelectronic circuit and modulation circuit of the fiber optic current transformer (FOCT) are easily affected by the complex environment in the converter station during operation, leading to abnormal operation and fault warning. In order to analyze the error characteristic on the output signal and harmonics of FOCT, the output signal models of FOCT with sine modulation in steady-state and error-state are established respectively in this paper. Combined with the output signal, the key parameters are solved, and it is pointed out that the change of photoelectric circuit may cause the ratio error. The Faraday phase shift and the change of the modulation circuit may cause the drift error. The error characteristics of the FOCT under different influencing factors are simulated and analyzed. The results show that output signal of FOCT is influenced by photoelectric circuit, Faraday phase shift circuit and modulation circuit. Changes in the photoelectric circuit will cause a proportional change in the FOCT output signal and harmonics. Both the Faraday phase-shifting and the increasing of modulation amplitude will reduce the minimum value of output signal. Changes in Faraday phase shift will cause an approximately proportional change in first harmonic. Changes in modulation signal amplitude will cause the harmonics to appear attenuate and oscillate. The modulation frequency is inversely proportional to the period of the output signal and harmonics. Both the first and second harmonics can be used as the monitoring state parameters of fault determination. Designed experiment verified the correctness of the conjecture. This article provides a theoretical basis for the follow-up status monitoring and fault diagnosis of FOCT.