| With the development of EHV or UHV at home and abroad, gas insulated substation (GIS) used widely, at the same time a new failure are born. The electric equipment is easily caused fault by very fast transient over-voltage (VFTO), with the enhancements of rated voltage, due to the operation of disconnector above 330kV GIS. Therefore the phenomenon of VFTO must be taken into consideration during the project of GIS.In order to accurately analyze VFTO, it is essential to find the equivalent models of each individual GIS component. Currently, for Metal-oxide Surge Arrester (MOA), there are two models in common. One is nonlinear resistance that based on static V-I characteristics, and the other one is capacitance to earth. The two models both unilaterally take one of them as the electrical performance, but it couldn't reflect MOA transient characteristics in high frequency domain of VFTO.Firstly, starting from the structure of MOA in GIS, electronic relaxation polarization is found in grain boundary under high frequency electric field, through analyzing the microstructure of MOA valve. Based on the polarization theory in alternating electric field, combined with the current response process of the grain boundary layer in high-frequency voltage, MOA transient circuit model is composed. The parameters of the polarization are calculated by dielectric spectroscopy. By making the theoretical analysis of the simulation current wave under the steep voltage,the model is verified that it can effectively reflect polarization process under VFTO.Then, combined with a GIS in China, VFTO is separately calculated when MOA is equivalent to shunt capacitance, non-linear resistance and transient model. The influence of MOA transient circuit model on VFTO is analyzed. By calculating VFTO on the situations of whether there is MOA at transmission line or not, the inhibit effect of MOAT and MOAG on VFTO is separately analyzed at the aspects of VFTO waveform, amplitude, and gradient. Finally, the best configuration of MOA is achieved. Combined with the characteristics of wiring in the GIS, VFTO under many kinds of operating mode is calculated, and the equipments of larger VFTO is mainly considered. Then the equipment's VFTO is calculated when MOA is on the different positions at the bus. The amplitude of VFTO is analyzed with weighted average, and the best configuration is obtained. |
PDF Full Text Request