Study On Image Detection Method Of Linear Optical Current Transformer

With the development of China's electric power industry,it's capacity and voltage are enhance constantly,therefore the traditional electromagnetic current transformer's shortcomings are exposed gradually.Optical current transformer is a research focus in the equipment of smart grid with advantages of simple insulated structure,strong electromagnetic interference resistance,no magnetic saturation,wide band of measurement,ect.At present,linear OCT based on the radial polarizer detection uses polarization technology(hereinafter referred to as linear OCT)to make Faraday Rotation Angle change into the synchronous rotation of the light spot image,which overcomes some drawbacks of the traditional light intensity detection model,such as narrow measurement range,nonlinear,light power correlation,linear birefringence and temperature drift,etc.However its image detection method still has some shortages,includeing high cost,big error of the algorithm,needing convert the image,resolution restricted by the number of optical fiber image converter and charge coupled device carmer's pixel,especially when measuring low current,the error caused by insufficient resolution can not meet the s-class accuracy.In order to fix these problems,a new method based on four-quardant decrector,called FQD,is proposed in this paper,the technical route is:there is a output current which is proportional to the light energy in the each quadrant photoelectric diode when the spot image irradiating FQD.After dealing with the algorithm,faraday rotation angle will be calculalated,so as to realize the current measurement.This method has the advantages of low cost,simple algorithm,high resolution and high precision.This paper makes the image detection method of linear OCT as the research object,expOounding the principle of image detection systcematically aind discussing the influence of dark zone,installation position and the light spot size to the measuring accuracy.It has been verified that the image detection method based on FQD makes the measuring accuracy promote from 0.5 to 0.2S class,and its error is 0.55%approximately within the of 1%-120%of the rated current of 300A.The measured resolution is nearly 100 times higher than the traditional one.Finally,this paper studies the temperature characteristics of FQD and establishes a mathematical model through the rate equation of current carrier.The researchs show that the change of emperature influences the the dark current and the photoelectric conversion coefficient of FQD mainly,which affects the measurement result.The measuring errors caused by the change of temperature are related to the dark current,the incident light power and faraday rotation angle.This paper obtains the data of measuring error by the experiment under the different light power within the range of-20??80?.The error curve with the variation of temperature and light power is obtained by the root mean square of measuring error.The necessity of temperature compensation is pointed out from the experimental results.