Research On High-Accuracy Adaptive Optical Current Transducer And Its Operating Stability

Being no saturation under fault current conditions and high level of insulation, Optical Current Transducer (OCT) has been thought as the appropriate substitute of the electromagnetic current transformer. However, the outside factors, such as environment temperature, make so much influence on the precision and stability of OCT that baffled its utility in power system. In this paper, for the first time, it is proved that OCT is an open loop system, so that the Adaptive Optical Transducing Principle on Independent Variables and the Solenoid Collecting Magnetic Field Optical Transducing Principle are presented. Based on the above two principles, the methods are gained to improve the precision and stability of OCT, and the new Adaptive Optical Current Transducer (AOCT) had been developed.Based on the mathematic model of OCT, it is proved that OCT is of the open loop characteristic, which for the first time explained the reason why OCT itself can not meet the demand of precision used in practice. Since it is impossible for OCT itself to realize a close loop structure, the only way to improve the precision of OCT is with the help of the new independent variables.The Adaptive Optical Transducing Principle on Independent Variables is presented in this paper, and a new Adaptive Optical Current Transducer (AOCT) has been developed with the new independent variables introduced to OCT, in which the precise power frequency current offered by a reference model of steady state is benchmark, and the measured harmonious and transient currents from optical transducer might be adjusted adaptively applying the adaptive arithmetic, so that both the steady state and transient precision of the AOCT has been improved. In order to satisfy the veracity and the robustness against time-variable noise of the AOCT, a new square root Kalman adaptive filter arithmetic with time-variable noise statistic is presented in this paper. In addition, the Wavelet analysis is applied to inspect the singularity of the measured current, and an adaptive signal-noise decomposer for AOCT is designed.For the first time, the Solenoid Collecting Magnetic Field Optical Transducing Principle is presented in this paper, and it is proved that the way to measure current by polarized light encircling conductor and that by polarized light threading solenoid axes are equivalent. The optical structure on solenoid collecting magnetic field is designed applying the above principle, which can improve the stability of AOCT greatly.According to IEC660044-8, the performance of AOCT is examined roundly applying the standard testing system authenticated by the state authority. The results indicate that the measurement precision of the AOCT has already reached 0.2 class.At present, the AOCT had been installed in a substation in BaoDing city HeBei province and has been working continuously over one year. The measurements had shown that the methods to improve the performance of OCT are correct and the AOCT designed in this paper is of excellent characteristics.