Study On The Influence Of Geomagnetic Storm Extremes Model And Three-Dimensional Earth Conductivity Model On Geomagnetic Induced Current

Extreme geomagnetic activity will induce the geoelectric field on the surface,and the resulting geomagnetic induced current(GIC)will threaten the normal operation of the power system.Existing studies often use the assumption of a uniform electric field of 1V/km to calculate GIC,or analyze a specific geomagnetic storm event.When conducting risk assessment on actual engineering problems,it is necessary to consider the small probability that extreme events may occur.Therefore,It is essential to study the extreme value of the geomagnetic field and the GIC distribution of the power grid under extreme magnetic storms to provide certain guidance for the protection of the GIC.Solving the induced geoelectric field caused by a magnetic storm is the prerequisite for calculating the GIC of the power grid.First,based on the observation data of domestic and foreign geomagnetic observatories,the characteristics of the geomagnetic field change during two typical magnetic storms in recent years are analyzed,and the plane wave method is used to obtain the induced geoelectric field during the magnetic storm.And the results show that the rate of change of the horizontal component of the geomagnetic field is the most relevant quantity to the induced geoelectric field.Secondly,the Lanzhou Geomagnetic Observatory is selected as an example,and the generalized Pareto distribution is used to fit the observation data,then peak-over-threshold models of the horizontal component of the geomagnetic field and its rate of change are established,and the return levels of different years are obtained.Through model checking,it is believed that the peak-over-threshold model is suitable for fitting the geomagnetic field,and the results show that the extreme level of the geomagnetic field change rate increases nonlinearly with return periods.Based on the extreme value results of different geomagnetic stations in mid-latitude regions,the range of the minute change rate of the geomagnetic field during the 100-year extreme magnetic storms and 200-year extreme magnetic storms are given.Finally,based on the electrical conductivity in North China,the three-dimensional earth model is established,and the induced geoelectric field under different extreme magnetic storm scenarios are calculated.Moreover,the nodal admittance method is used to compile the GIC calculation program.By calculating the equivalent voltage source of the induced geoelectric field,the GIC in the UHV grid in North China are obtained.The results show that the lateral change of the earth's conductivity leads to a significant change in the distribution of GIC in the power grid compared to the uniform electric field.The calculation results can provide a certain reference for the suppression and management of GIC in the UHV grid in North China.