| Gas insulated substation has been widely used in power system because of its compact structure,small area and reliable operation.However,when disconnectors are switched on and off in GIS,Very Fast Transient Over voltage(VFTO)with high-gradient ? high amplitude and high frequency will be formed,which will endanger the normal operation of electrical equipment.Transient Enclosure Voltage Rise(TEV)can also be produced by coupling the GIS shell,which can easily cause secondary equipment insulation damage and endanger the personal safety of operators.Therefore,it can effectively ensure the safe and stable operation of power system,and also provide some reference for the long-term construction and maintenance of UHV GIS by accurately calculating the amplitude-frequency characteristics of VFTO and adopting reasonable and effective suppression measures.In recent years,GIS is mainly developing towards high voltage,large capacity,three-phase enclosure and miniaturization,while the research on VFTO at home and abroad is mostly aimed at three-phase split GIS structure.In this paper,we establish a500 kV GIS calculation model considering three-phase bus coupling.Clark transform is used to decouple three-phase.The amplitude-frequency characteristics of VFTO are analyzed.The effects of parameters change and suppression measures on the amplitude-frequency characteristics are also studied.The results show that the frequency of VFTO distributes in the range of 0-50 MHz and concentrates in the range of 0-5MHz.The maximum amplitude of VFTO is 2.41 p.u.;the increase of transformer entrance capacitance,bus length and disconnector capacitance will reduce the VFTO amplitude;the increase of bus residual voltage modulus will increase VFTO,and the increase of residual voltage will cause the increase of VFTO amplitude in typical frequency band;the VFTO of three-phase will all increase when the power supply voltage is zero-crossing.When the closing time is at the minimum value,the larger the power supply voltage is,the higher the VFTO is.The amplitude of time domain and amplitude frequency characteristics of VFTO decrease with theincrease of shunt resistance and show a certain saturation effect,which is suitable for200~500?.The addition of lightning arrester can also limit the VFTO amplitude to a certain extent.The above factors have little effect on the overall distribution of VFTO frequency,but the VFTO amplitude at the corresponding frequency points has changed.Secondly,by adding ideal transformer,the internal circuit,the shell circuit and the overhead line are connected together to simulate the electromagnetic coupling between each other.The GIS simulation model is re-established,and then the TEV amplitude-frequency characteristic is calculated.The results show that the TEV frequency distribution is 0~50MHz,concentrated in 0~5MHz,and the maximum amplitude is up to 0.076 p.u..After adding closing resistance,the TEV amplitude decreases and the frequency distribution changes obviously.The TEV amplitude decreases with the decrease of equivalent inductance of grounding leads,and the increase in the number of grounding leads in parallel can also play a good role in suppressing the amplitude and frequency of TEV.The effect of paralleling 2 to 3 is more obvious. |
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