Optimum Design Of The Inner Electric Field In The Sensing Head Of Optical Voltage Transducer

With the continuous improvement of the transmission capacity and voltage level of power system,the traditional voltage transformers have exposed some faults gradually,such as poor insulation performance,bulky,electromagnetic resonance,magnetic saturation,etc.They are difficult to meet the needs of the development of smart grid.Optical voltage transducers(OVTs),adopting optical sensing technology,can overcome those defects,so that they will satisfy the development requirements of China's smart grid and have good development prospect.But there are still many unresolved problems in OVTs,such as stress birefringence,temperature drift,connection stability of optical devices and uniformity of the internal electric field distribution,which would affect the measurement results,reduce the stability of longtime operation,and restrict the practical application of OVTs.In view of the problems of measurement accuracy and stability of longtime operation of OVT,the connection stability of the optical devices and the internal electric field distribution based on existing OVT structures are selected as the research focus in this paper.When the electric field distribution in the selected OVT sensing head is not uniform,the measurement errors caused by the offset of BGO crystal and optical path are systematically analyzed.And then the methods of improving the electric field distribution and the measuring error are presented for two different OVT structures.Firstly,the basic principle of the Pockels OVT is analyzed,and then the multi-segmented Pockels OVT in longitudinal modulation without capacitance differential pressure,presented by Josemir Coelho Santos,is selected as the research emphasis after fully discussing the advantages and disadvantages of some common OVT structures.Then,the electric field distributions in the sensing head of the multi-segmented OVT are analyzed,and the influences of the inhomogeneity of the electric field on the measurement results are discussed in detail.In addition,when the position of the crystal or the incident angle has a small deviation,the integral voltage errors are 0.26%and 0.18%,respectively,which make sensing accuracy can't meet the requirement of 0.2 accuracy level.In order to improve the electric field distribution in the sensing head and reduce the integral voltage error,the new method of quartz glass medium stratification is proposed.The effectiveness of the method is verified both by ANSYS Maxwell and by experiment,and the integral voltage errors can be reduced to 0.01%and 0.04%,respectively,meeting the requirement of the 0.2 accuracy level.Finally,a new type of 110kV OVT without capacitance differential pressure,which is based on the principle of convergent polarized light interference,is presented by our research team and introduced in the paper.The analysis of the electric field distribution in the sensing head is simulated by ANSYS Maxwell.And to improve the electric field distribution and reduce the integral voltage error in this structure,another new method of medium wrapping of electro-optic crystal is proposed,in which the Alumina ceramic is selected as the medium.The simulation results show that the integral voltage error is reduced to less than 0.2%,which can fully guarantee the measurement accuracy of 0.2,and improve the reliability of longtime work for OVT.