Investigate On A New Method To Improve The Reliability Of EVT By Reducing The Capacitance Based On Equal Potential Gradient Shield

With the development of smart grid technologies,plenty of electric voltage transformers(EVT)have been used in power grid in recent years.However,the current situation shows that the safty and reliability of EVT should be improved for better engineering application.In view of this situation,researches and applications on EVT are summarized in this paper.The electronic capacitive voltage transformer is taken as research object,and the technology roadmap is that the capacitance is reduced to improve EVT’s reliability.Typical breakdowns of EVT has been further analyzed,including comprehensive performance test and breakdown collection have made it clear that transient over voltage,over current and the strong electromagnetic interference are the key factors that influence the reliability of EVT.These transient impulses has a prominent influence on capacitive divider EVT.So a simulation has calculated the characteristics of electronic capacitive voltage transformer under the condition of transient over voltage.The results further demonstrated the necessity to reduce the capacitance of EVT.Stray capacitance is the main factor affecting the accuracy and stability of EVT in the process of operation.Thus,a new method to improve the reliability of EVT by reducing the capacitance based on equal potential gradient shield has been proposed.Three detail structures to realize equal potential gradient shield has been discussed.Consideration about the technological level,shielding effect,cost and so on,a cylinder structure has been adopted.This paper has stated the key points of the cylinder parameters design,and the design rule is analyzed according to the electric field distribution,insulation safety and capacitor value.According to the researches above,this paper has designed the specific parameters of 110 kV low capacitance EVT and equal potential gradient shield,The 3D electric field model of capacitive divider has been set up.According to the requirement of engineering application,High performance computing server helped to analysis the influence of equal potential gradient to capacitive divider in view of electric insulation and anti-interference,The good anti-interference of equal potential gradient structure has been proved.According to the research results above,low capacitance EVT prototype has been made out and tested,the result has shown that that 110 kV EVT with dual capacitive screen and 300 pF main electrical capacity can meet the error requirements of class 0.2.It can be found in the process of the research above that equal potential gradient structure can improve the insulation performance of capacitive divider,the result is also applicative in insulator.Therefore,the principles which can improve the insulator’s electric field distribution based on potential gradient shield structure is analyzed,and the optimal design rule of the shield structure is confirmed,which is validated by simulation.