全光纤电流互感器温度特性建模分析与实验研究

Modeling Analysis and Experiment Study on Temperature Characteristic of All-fiber Optical Current Transformer

建立了全光纤电流互感器（fiber-optical current transformer,FOCT）温度特性的数学模型。该模型充分考虑传感光纤的弯曲特性,结合光纤线性双折射的分布参数模型从本质上解释了温度对线性双折射的影响机理：由于传感环的弯曲性,温度变化会导致光纤横截面上的受力不对称,进而引起线性双折射;单位长度光纤的线性双折射相位差与温度变化量成正比,与光纤弯曲半径成反比。并结合光纤Verdet常数的温度特性综合量化了温度对FOCT的影响。采用COMSOL有限元分析方法实现光场、磁场、温度场、应力场的耦合并分析求解。仿真结果表明：双折射效应会使光波旋转角变小;光纤横截面上的应力差与温度变化量成正比,与光纤弯曲半径成反比;温度波动将引起线性双折射,进而使光波旋转角减小;结合Verdet常数得到了温度波动时FOCT的综合误差,与理论分析结果吻合。最后设计并搭建FOCT实验平台,进行线性度测试和温度循环测试。测试结果表明：实验误差与理论误差变化趋势基本一致;温度波动越大,FOCT误差漂移越严重,必须采取补偿措施,故提出一系列改善FOCT温度稳定性的方法。仿真与实验结果验证了理论分析的正确性。

Temperature characteristic model of FOCT was established, where bending characteristic of sensing optical fiber was analyzed comprehensively. Temperature＇s effect on linear birefringence was explained with the distributed parameter model of optical fiber＇s linear birefringence in essence. Due to the bending characteristic of sensing coil, linear birefringence is resulted by asymmetric stress on optical fiber＇s cross section which is caused by temperature fluctuation. Phase difference of linear birefringence in unit length optical fiber is proportional to the variation of temperature and inversely proportional to the radius of the bending optical fiber. Temperature＇s effect on FOCT was quantified with temperature characteristic of Verdet constant. By using COMSOL, the coupling of optical field, magnetic field, temperature field and stress field was realized with finite element method. The simulation result shows that the optical rotation angle is decreased by linear birefringence, and the stress difference on optical fiber＇s cross section is proportional to the variation of temperature and inversely proportional to the bending radius of the optical fiber. Optical rotation angle is decreased with linear birefringence which is generated by temperature fluctuation. Besides, composite error of FOCT which was obtained by Verdet constant are accorded with theoretical analysis. Finally, experiment platform of FOCT was designed and set up. Linear test and temperature cycling test were performed. The changing trend of experimental error is basically agreed with theoretical error. The larger the temperature variation is, the larger the FOCT error will be. Compensatory measures must be taken in order to improve the temperature stability of FOCT. The correctness of theoretical analysis is verified by the results of simulation and experiment.