Analysis Of The Distribution Characteristics Of Induced Geoelectric Fields During Geomagnetic Storms Based On Magnetotelluric Sounding Method

Geomagnetic storms will generate induction electric field of magnetic storm in conducting mediums like field,which results in geomagnetically induced current(GIC)when applying in the loop consists of transmission line,neutral grounding transformer and field.The geomagnetically induced current is a giant threat to the safe operating of the power grid and its equipment,including relay protection equipment malfunction,overloading of capacitor bank and SVC(Static Var Compensator),overloading of the capacitor in the AC at the end of the HVDC(High Voltage Direct Current)station,voltage fluctuation of the power system and so on.As the 1000kV extra high voltage transmission line in China is being built and brought in service,the power grid of our country will face a growing risk from geomagnetic storms,for the long tramsmission distance and the small unit resistance of extra high voltage transmission line.As a result,it’s of significance to study the influence that magnetic storms have in the power,guarantee the safe operating of the power grid and calculate as well as analyse the distribution rule of induction electric field quickly when precisely.The key to prevent geomagnetic hazards is finding the precise distribution of the geomagnetic field.The distribution used to be resolved by building the electrical structrue of the field by the inversion of MT(Magnetotelluric sounding),then calculating with finite element calculation,which needs formidable quantity of work,causing low economic benefits when applying in engineering.To cut down the complicated process of model building and calculating and increase the economic efficiency in engineering,this dissertation introduces the electromagnetic sounding parameters measured actually with MT.After counting the actual measuring curve of electromagnetic sounding in Chinese mainland and analysing typical electromagnetic sounding curve,it’s found that the curve varies a lot in value from 10-0.5 to 104 ohm and the electromagnetic sounding curves of ρxy as well as pyx lays close in high band with good coincidence while branching apparently in low band.The actual electromagnetic sounding data from MT is corresponding to the frequency.At the frequency domain,the induction geomagnetic field data can be calculated straghtly with the actual magnetic data measured by geomagnetic observatory or other geomagnetic measuring equipments.It not only simplify the calculation of the electrical field inducting by magnetic storms,but also lays the foundation of calculating the geomagnetic inducting current in the power grid so as to research its effect on the power grid further.Based on the data observed by several geomagnetic observatories during the magnetic storm in 2004,this dissertation calculates the relative inducting geomagnetic field according to the data from the geomagnetic observatory in Guangzhou and then chooses the time ranges when the relative inducting geomagnetic field data exceeds threshold as chosen magnetic data to Fourier transforming the data from the seven geomagnetic observatories in China.Through analysing metioned above,it’s found that main geomagnetic frequency domain component amplitude concentrate upon the frequency domain from 10-4 to 10-3,in which the magnetic field is more likely to induce larger geomagnetic field on the ground.By calculating the distribution of geomagnetic field on the ground inducted by magnetic storm and the MT data from Northeast China,North China,East China,Central China,South China and Northwest China,this dissertation finds that the inducted geomagnetic field on the ground splits greatly,while north,east,central and south area appear to have a larger inducted geomagnetic field,but northeast and northwest area a smaller one.Based on the observation second data of several geomagnetic stations during the 2004 geomagnetic storm,the relative induced geoelectric field is calculated according to the geomagnetic data of Guangzhou geomagnetic station during the 2004 geomagnetic storm.The time period when the induced geoelectric field value exceeds the threshold is selected as the selected magnetic field data to Fourier transform the corresponding magnetic field data of seven geomagnetic stations in China.Through analysis,it is found that the amplitude of the larger frequency domain components of the geomagnetic field is concentrated in the 10-4--10-3Hz frequency domain,and the magnetic field in this part of the frequency domain is more likely to produce a larger induced geoelectric field.Based on the magnetotelluric sounding data collected in Northeast China,North China,East China,Central China,South China and Northwest China,the distribution of induced geoelectric field is calculated.It is found that the distribution of induced geoelectric field is very uneven,and the value of induced geoelectric field in North China,East China,Central China and South China is larger than that in other regions,while that in Northeast China and Northwest China is smaller.