The Development Of The External Capacitor Divider Based On The GIS Insulator Stray Capacitance

Along with the rapid development of China's UHV technology and the increasing shortage of urban land,GIS substation will become the future trend of substation construction in China.However,gas-insulated switchgears in operation are not only threatened by power-frequency overvoltages,but also may be subjected to transient overvoltages such as operation and lightning at any time.Once these overvoltages cause insulation damage to the equipment,Substations and grids will be dangerous.Therefore,it is necessary to study the overvoltage in GIS,and the primary task of the research is to measure these overvoltages accurately.At present,Sensors cannot be quickly loaded and unloaded through existing methods,which brings difficulties for on-site measurement.In order to solve the problem of inconvenient loading and unloading of sensors,this thesis proposes a new measurement method,which place the sensor outside.The external electrodes of the sensing electrode and the low-voltage arm capacitor make it easy to disassemble the voltage divider.By analyzing the divide transfer function,the influencing factors of its frequency characteristics are obtained.Refer to the above result,the divider structure and the back-end circuit are optimized.Reference to the non-inductive resistance method,the stray inductance of the low arm is reduced;the introduction of the voltage follower increases the time constant of the low arm.Through the finite element analysis software,the applicability of the method under different GIS structures and sizes is compared.According to the results,this method is more suitable for open insulators than insulators with metal rings.For three-pole common box GIS,when using three divider for measurement,the composite signal needs to be decoupled.The thicker the insulator,the thinner the shell at the flange,the more favorable to this method.Reference results,select a representative structure and dimensions to build a solid GIS model.Based on solid GIS model,the parameters of the sensor are configured,and the frequency characteristics and voltage ratio of the configured sensor are calibrated.According to the configuration result,the sensing electrode size is 10*20mm,the high-arm capacitance is 0.005 p F,the low-voltage arm capacitance is 1n F,and the back-end equivalent resistance is 5M?.The calibration results show that the high cut-off frequency of the divider can reach 1.16 MHz,and the low cut-off frequency can be as low as 30 Hz,the voltage ratio is stable at high and low frequencies,which meets the requirements of transient voltage full-wave measurement.