Research On Sagnac Type Fiber Optical Current Sensor

Fiber optic current sensor (OCS) is a current sensor used in National Grid, which playsan important role in electric power system. At present, traditional electronic currenttransformer (CT) has reached a mature state, but it faces some difficulties such asminiaturization and safety. Compared with CT, Fiber optic current sensor, which use opticalfiber as the transmission and sensing medium has great predominance in miniaturization andsafety. Therefore, the research on OCS is of great significance. The performances of\opticaldevices in the system and environmental factors such as vibration and temperature have greatinfluence on the sensing signal. So a number of key issues in those were studied in thisdissertation, detailed as follows:1. The theoretical modal was analyzed in detail. Each optical device and sensing systemtheoretical modal were established according to Jones matrix theory. The output error basedon performance of devices was simulated and the curved which represent the effecting rulesare theoretically acquired. According to the simulation results, it was found that the jointingerror of splitter and the phase delay of the wave plate should be in0.05and0.3°, for the errorin0.2%.2. For the adverse environmental factor, the corresponding error suppressionscheme was put forward. For the influence of vibration, the additional fiber compensationcoil was proposed to suppress the error. The theoretical analysis and the correspondingexperimental tests were realized where there was current and no current in the wire. Theresults showed that the new scheme could suppress the extra vibration effects obviously. Thetheoretical analysis of the influence of temperature on the optical sensing coil was done. thesimulation result showed that the heat-reactivity of rotating rate was much bigger than theradius of the coil. For the output bias due to temperature changing, the wavelet neuralnetwork was induced into the output error compensation, and the error after compensationwas in±0.5A.3. The influence on the theoretical modal of performance of power source and thesuppression of resource intensity noise were researched. According to the theory of wavedispersion, the influence on the system of optical power source wavelength was analyzed.The result showed that the reflective index of the medium became smaller with the increaseof wavelength and the gradient becoming small too in the larger wavelength range. So, thebigger wavelength optical fiber source was the best choice for the stability of scale factor. Forthe stability of power wavelength, a new stepped-in PID control method was proposed, the new method could keep the temperature of the pump in the range of±0.05℃and make thepower source has good wavelength stability. For the suppression of resource intensity noise,in combination with relativity between signals, the new method of adding an extra polarizerafter the coupler was proposed. The new method could suppress the noise vastly.4. The winding method of fiber coil was analyzed in detail and the realization of windingmethod of two fiber coils with QAD was researched. The optimization methods in signalprocessing, PCB design and so on were researched. For the de-nosing of the output data ofoptical current sensor, the wavelet threshold de-noising method was induced into the outputdata processing and a new threshold function was proposed. Comparison to the ordinaryfunction was done and the de-noising results were analyzed using the method of Allanvariance.