Study On Measuring Methods Of VFTO In GIS

With the rapid development of power industry and constantly increasing of voltage class in our country, Gas Insulated Substations (GIS) have been widely used in power system. With the increasing of GIS voltage class, some switching operations or line to enclosure faults in GIS may cause Very Fast Transient Over-voltages (VFTO), which may seriously damage the operation safety. So it is quite necessary to study the measurement of VFTO in GIS.This paper first introduces several different measuring systems and shows the circuits and measurement principle. The simulation model is built to analyze the step response of the measuring system and all the factors which affect it. By comparing the different measurements, the advantages and disadvantages can be observed. The study result shows that the step response character of the cone probe capacitor voltage divider is quite well which rarely influenced by stray parameters. However it is difficult to match with transmission cable and non-convenience for installation. The circular probe capacitive voltage divider is easy to install. However it is also difficult to match with transmission cable and the step response has oscillation. The D/I measuring system is easy to install, but stray parameter may seriously influences its step response.Then a flake probe voltage divider measuring system is proposed. It can be easily installed and avoid the oscillation in step response. A square wave generator and a full scale GIS model is also designed for step response experiment of measuring system. With the help of ATP simulation the factor which affects step response of measuring system can be analyzed. The result of experiment shows that the step response of the flake probe capacitor voltage divider meets the design requirements, which rising time less then 5ns and steady time less then 20ns; therefore it is suitable for the measuring of VFTO.