Research On Electro-optic Sensing Method Of Intense AC/DC Hybrid Electric Field And Device Fabrication

With the development of national economy,the problem of unbalanced distribution of energy center and load center is becoming increasingly prominent.In order to realize the optimal allocation of resources and the optimal supply of energy in the whole country,it has become an inevitable trend to build a high voltage,large capacity and long-distance power transmission.However,due to the limitation of land resources,more and more AC and DC transmission lines are built on the same tower or in the same corridor.The problem of hybrid electric field in the transmission corridor has become a restrictive factor in the construction of the project.Effective electric field measurement technology is urgently needed to evaluate the electric field environment of the transmission corridor to guide the construction of the project.In this paper,an electric field sensing method based on Pockels effect and electric field modulation is proposed for the measurement of intense AC/DC hybrid electric field.The electric field sensor is trial manufactured,which can realize the simultaneous measurement of AC and DC electric field strength.At the same time,the factors affecting the overall performance of the sensor are analyzed,and the corresponding optimization methods are proposed.The main contents of the paper are as follows:(1)The electro-optic sensing method for AC/DC hybrid electric field is proposed.The theoretical analysis model of electro-optic conversion unit and electric field modulation unit is established and introduced in detail.The mathematical expression of the input-output relationship of the sensor is deduced,which provides the theoretical basis for the design and manufacture of the sensor.(2)The related devices are selected and fabricated to realize packaging of the electro-optic conversion unit and the electric field modulation unit.And the related performance tests are carried out.The results show that the electro-optical conversion unit can accurately measure the electric field in the range of 0.5～300 kV/m and the response to the change of the electric field is rapid and the frequency characteristic is good.The electric field modulation unit operates stably,the rotating speed is constant and reliably grounded,both of which meet the design requirements.(3)The combination of electro-optical conversion unit and electric field modulation unit is tested to realize the simultaneous measurement of AC and DC electric fields in 150 kV/m.The input and output of the sensor have good linearity and realize the judgment of the polarity of the DC electric field.The maximum measurement error is less than 3% with time delay less than 0.2 s.The minimum measureable AC and DC electric field intensities are 1.23 kV/m and 1.05 kV/m respectively,which can meet the demand of the AC/DC hybrid electric field intensity measurement in the engineering.(4)The influence of noise,light intensity loss and temperature characteristics of the electro-optic conversion unit on the sensor performance is analyzed,and the corresponding optimization measures are proposed.Three-dimensional finite element simulation model is established on Comsol to calculate the electric field distribution under the rotating grounded electrode and analyze the electric field modulation efficiency.The influence of electrode spacing and the number of vanes in the electrode on the performance of the sensor is studied,which provides a basis for the overall packaging of the sensor.