Key Technology Research Of Optical Current Transducer Based On Magneto-optical Rotation Effect

Due to the disadvantages of traditional electromagnetic transducer,such as high cost,high insulation requirements,ferromagnetic resonance and serious magnetic saturation,it gradually exposes the phenomenon of mismatch with the development of power grid.Compared with traditional electromagnetic current transducers,optical current transducers mainly use optical technology,which has many superiorities such as simple structure,high insulation level,good anti-interference ability,fast response time,and digital signal.It has become a new research and development focus of China’s smart grid technology.At present,the mainstream optical current transducers are mainly based on the magneto-optical rotation effect,which achieves the purpose of current measurement by measuring the magneto-optical rotation angle using a light intensity detection mode.However,this measurement mode must control the magneto-optical rotation angle within a very small angle range,in order to utilize the equivalent infinitesimal property of the sine function to achieve approximate linear measurement.Therefore,the research purpose of this article is to explore the demodulation method of magneto-optical rotation angle in optical current transducers derived from light intensity detection mode,in order to solve the problems of large current measurement errors and limited range in approximate linear measurement methods,so as to reduce current measurement errors,defeat the constraints of current measurement range,and achieve linear measurement of current.Firstly,the characteristics of polarized light,general mathematical description methods,and matrix forms of special polarized light and polarization devices were analyzed.Then,the mechanism of the magneto-optical rotation effect and the principle and basic structure of the magneto-optical current transducer were analyzed using a matrix.The output light intensity signal equation of the magneto-optical current transducer was derived,and the output light intensity signal containing magneto-optical rotation angle information was processed using a single optical path detection method.This lays a theoretical research foundation for further conducting current measurement based on integral reconstruction of magneto-optical rotation angle and reducing the influence of Fresnel effect on nonreciprocal magneto-optical rotation angle by changing the polarization direction of linearly polarized light based on polarization beam splitter.Secondly,a current measurement method based on integral reconstruction of the magnetooptical rotation angle is proposed to address the problem of approximately linear measurement of the magneto-optical rotation angle in the light intensity detection mode.The method is based on the derivative of a sinusoidal signal containing the magneto-optical rotation angle and the use of trigonometric equivalent deformation to eliminate the cosine term in the derivative,and finally the integral reconstruction of the magneto-optical rotation angle is utilized to achieve the current measurement.The results reveal that the measurement error is less than 1.30% in the current range of 0.20 Arms ～ 2.40 Arms,and the magneto-optical rotation angle has a good linearity of 99.987% with respect to the current.Compared to the approximately linear measurement method,the integral reconstruction method reduces the measurement error of the current.Finally,aiming at the error caused by the Fresnel effect in the measurement of nonreciprocal magneto-optical rotation angle in the reflected optical path,a method based on the polarization beam splitter to change the polarization direction of linearly polarized light is proposed to reduce the Fresnel effect.This method mainly uses a polarization beam splitter to separate the vertically linearly polarized light generated by the anisotropy of the mirror multilayer coating in the He-Ne laser tube,and incident the vertically linearly polarized light onto the beam splitter,thereby reducing the error caused by the Fresnel effect in the measurement of the nonreciprocal magneto-optical rotation angle during the reflection process by changing the polarization direction of the incoming ray polarized light.The experimental results show that the influence of the Fresnel effect on the nonreciprocity of the Faraday magneto-optical rotation effect is reduced by changing the polarization direction of the incoming ray polarized light,and the multiplication of the magneto-optical rotation angle is achieved.At the same time,compared to the straight through optical path structure,the reflective optical path improves the current measurement sensitivity by utilizing the nonreciprocity of the magneto-optical rotation angle,while reducing the current measurement error.