Research On Suppressing The Very Fast Transient Overvoltage In GIS By Magnetic Rings

With the rapid construction of ultra-high voltage network in our country,the gas insulated switchgears are widely used in power systems,because of the advantages of small floor area,simple maintenance and high safety performance et al.However,the very fast transient overvoltage which is caused mainly by prestrikes and restrikes during switching seriously threatens the insulation safety of substations and external devices,and it should be suppressed.In order to overcome the defects of the VFTO protection technology,some experts put forward to install the magnetic ring on the internal GIS pole to suppress the VFTO.The paper carried out the field test and simulation research to verify the feasibility of magnetic ring,and lays the foundation for the application of the magnetic ring device in the GIS substation.The paper carried out series of field experiments by the test platform which consist of 2 MV Marx generator and 550 kV GIS,and analyzed the influence of magnetic rings on the amplitude and gradient of VFTO by the test data.Then,the paper used EMTP software to build the simulation model of impact voltage test circuit,and on the basis of this,the study presented a model of nonlinear magnetic ring,in addition,the accuracy of this model can be verified by compare with the field test data.The study analyzed the effect of the characteristic parameters of magnetic material on the suppression effect in detail.Then,combining with the diagram of a 550 kV GIS substation,the influence of the installation position and installation method of the magnetic ring on the VFTO was studied.The test results verify that the magnetic rings can suppress the amplitude and steepness of the VFTO in the UHV GIS.By compare with experimental data,the study also confirmed that the simulation model of the magnetic ring can accurately reflect the dynamic response of the ring under the VFTO,and basically meet the requirements of simulation.Lastly,the research on the simulation of nonlinear magnetic ring model shows that the ring may get better suppression effect which select lower initial permeability and high resistivity magnetic material.The paper also points out that the magnetic ring's location might affect suppression of ring on the certain overvoltage,and change the magnetic ring in the GIS conductive rod installation may be also beneficial to improve the suppression of VFTO.