Study On Very Fast Transient Overvoltage And Its Impacts In Ehv And Uhv GIS

With the improvement of rated voltage in power system, the ratio of the lightning impulse withstand voltage (LIWV) to the rated voltage is decreasing, which makes the problem of fast transient phenomenon in GIS more and more obvious and serious. Thus, the influence of VFTO must be taken into consideration in insulation designing of GIS.In this paper, the calculation results of very fast transient over-voltage for operations of disconnector based on 550kV GIS of Hydro-energy storage station and 800kV GIS of LanZhoudong station are presented, using EMTP and FORTRAN. Firstly, the refining models of components in GIS are set up according to the internal structures and characteristics of different equipments, and the equivalent parameters are obtained on the basis of the analysis on three dimensional electricfield, which make sure that calculation may be more accurate and valuable. According to the calculation data, the amplitudes and frequencies of VFTO occurred on different components in 550kV and 800kV GIS are compared, and the effects of EHV and UHV GIS structure on VFTO are also presented, which will provide reference to 1100kV GIS alternating current testing demonstration engineering. By analyzed variations of VFTO occurred on components in GIS and power transformer, the refining models and calculation parameters can be set up and chosen effectively.Secondly, transient enclosure voltage and interference voltage accompany VFTO in such high frequency transient field are also studied in this paper. Transient enclosure voltage (TEV) varies in the range of several tens kilovolt, which is much lower than the amplitude of VFTO. Therefore, it is no need to consider TEV in simulation of VFTO propagation. But the interference voltage occur on the secondary cable should be paid more attention because of the high amplitude and frequency, or the on-line monitoring and secondary protection system maybe destroyed.Finally, a fault of long-term persistent arcing in 550kV GIS is analyzed base on a refining model of double-break current breaker. The over voltage occurred on the main and auxiliary contacts of breaker is calculated and the problem of thermal capacity of the equalizing capacitor is discussed for the first time.