Modeling Analysis And Experimental Study On Sensing Mechanism Of All-fiber Optical Current Transformer

The fiber optical current transformer(FOCT)can measure the external current by using its unique property that the polarization direction of the linearly polarized light rotates when the light go through the magnetic field in the magne to-optical material,and compared to the traditional electromagnetic current sensor,FOCT has a great advantage in the insulation,anti-electromagnetic interference and reliability.Researchers have paid much attention to it in recent years.A distributed parameter model of FOCT based on polarization inspection method is established firstly and the distribution parameters of the transfer matrix of the sensing element are deduced with the polarization tensor and the Maxwell equations.The mechanism of the linear birefringence in the sensing unit is revealed.The validity of the distributed parameter model is verified by comparing with the macroscopic Jones matrix.Based on the theory above,the method to improve the measurement accuracy of FOCT is putting forward.Secondly,by using COMSOL,the coupling of optical fields and magnetic fields was realized,which provided the model foundation for the coupling of complex multi-physics fields in FOCT sensor units.A new method to calculate the rotation angle of the optical wave and the theoretical expression of rotation angle are proposed.By comparing the relationship between the rotation angle and transmission distance of L under different conditions,the influence of the measured current,linear birefringence,refractive index,optical fiber bending radius on the output rotation angle are analyzedBy using COMSOL,the coupling of the optical field,magnetic field,temperature field and thermal stress fields was realized,which provided the model foundation for the coupling of complex multi-physics fields in FOCT sensor units and the sensitivity of the optical fiber to the physical condition such as ambient temperature,stress and vibration is analyzed.Finally,the experimental platform of all fiber optical current transformers is set up and the light path test has been carried out,which lays a good foundation for the future research on the influence of the environment factors on the FOCT.