Research On Non-contact Overvoltage Monitoring Sensor Based On Electro-optic Effect

Measurement of overvoltage in high voltage power grid is of great significance tothe research on the characteristics of overvoltage and the design of insulationcoordination. With the rapid development of advanced optical technologies,Optoelectronic sensing technologies with strong anti-interference ability can be possiblyapplied in the overvoltage monitoring in power grid. Therefore, the optoelectronicconversion and coupling capacitor technologies are combined in this article to develop anon-contact overvoltage sensor and accurately measure overvoltage without powersupply.In this article, the basic principle of sensor is elaborated. The coupling capacitormethod is adopted to reduce the amplitude of overvoltage. Then, convert the lowamplitude overvoltage signal to optical signal with the electro-optic effect of specialcrystals. The optical signal is transmitted to signal processing unit by fiber, and finallythe original measured overvoltage can be back-calculated.The sensor consists of two main parts: the non-contact voltage division unit andoptoelectronic sensing unit. Considering the requirement of actual measurement, thestructure and parameter of non-contact voltage division unit is designed according to thecoupling capacitor method, and the power frequency voltage test and impulse voltagetest are carried out to acquire its voltage ratio and verify the accuracy. Meanwhile,LiNbO3crystal is eventually selected as the material to design the optoelectronicsensing unit. then, the optoelectronic sensing unit is Precisely packaged, and theperformance and accuracy to sense low voltage is verified. Finally the two parts arefitted together as a whole sensor, and test it under high impulse voltage. By comparingthe measured voltage with the voltage back-calculated by the output of senor, the senoris proved to have a high precision and high frequency response speed under bothlightning and switching impulse, which can satisfy the requirement of overvoltage inengineering application. The main achievements of this paper are as follows:①The high voltage signal is successfully transformed to low voltage signal as theinput source of optoelectronic sensing unit by the coupling capacitor method, The testresults indicate that the response time error of this method is within3%, and the peakvalue error is within2%. ②The voltage signal is successfully converted to optical signal according to theelectro-optic effect. The test results indicate that the optoelectronic sensing unit canaccurately measure an arbitrary voltage signal in [-20,20V], and the measuringfrequency can achieve MHz.③Combine the coupling capacitor technologies and optoelectronic conversion tosuccessfully measure the overvoltage in a non-contact way and with no power supplyneeded, then, the error analysis is conducted and some improvement measures areproposed.The amplitude and waveform of Overvoltage can be accurately acquired by thenon-contact optoelectronic voltage sensor proposed in this article with no power supplyneeded at the measurement site. The influence of electromagnetic interference small andthe sensor is electrical isolated from the primary equipment in electric power system,which is a great breakthrough in this field. The measuring results can effectively instructthe protection design of overvoltage and ensure the safe operation of electric powersystem.