Mid-low Latitude Power Grid Geomagnetically Induced Currents And Its Assessing Method

Geomagnetically Induced Currents(GIC) will threaten safe operation of power systems. In this paper,supported by National Nature and Science Fund(Project No:50677020, Study on Evaluation Model and Algorithm of GIC in UHV Power Grid),from two aspects of actual measurement and modeling calculation,characteristics and effect factors of GICs in mid-and-low-latitude power grids is investigated,and GIC evaluation method applicable for power grids in mid-and-low latitude regions is proposed,and GIC level in Northwest 750kV Planning Power Grid is estimated.The main research content is as follows:(1) Through study on GIC related events and monitoring data in Chinese power grids, although China is located in mid-and-low latitude,magnitude of GICs in power grids is high enough to threaten safe operation of power grids.Moreover,with developing of power grids and approaching of next peak solar activity cycle,the risk that power grids suffer from GICs will increase enormously,thus it is necessary and urgent to investigate GIC in Chinese power grids.(2) DC current monitoring data collected from neutral points of some transformers and geomagnetic storm data during many geomagnetic storms are performed comparative and relevant and statistical analysis sequently.The result shows that variation rate of horizontal geomagnetic component,conductivity of the earth and topology & parameters of power grids are main influencing factors,of which with weakening of geomagnetic activities in mid-and-low latitude regions,characteristics of the earth and power grids are more important influencing factors to GIC magnitude.(3) Fundamental equation of earth induced electromagnetic field is deduced,the relationships between electric and magnetic fields in uniform medium and one-dimension layered medium are established respectively,calculation method of earth surface electric field based on geomagnetic storm data is put forward.Then Zhaoqing geomagnetic storm data taken as scenario condition,GIC in Lingao Nuclear Power Station is calculated.And the calculated result matches well with measured data.It is obvious that the method has merits like better precision than that in high latitude regions,and less data requirement,and more convenient calculation.(4) Based on quasi-dc characteristic of GIC,equivalent models of components in power grids are set up,and power grid modeling and its simplification method are brought forward, and matrix equation solution in convenience of calculation is deduced.Then Jiangsu 500kV Power Grid taken as a case,GIC in Shanghe Substation is calculated,of which the result proves the validity of model and algorithm compared with measured data.(5) GIC level in Northwest 750kV Planning Power Grid under the effect of uniform electric field and strong geomagnetic storm is estimated.The result shows that during strong geomagnetic storms GICs flowing in most of transformers exceed allowable threshold value, which needs enough attention from relevant departments.With application of earth resistivity divisional model and geomagnetic storm data,spatial interpolation method diminishes errors caused by the disequilibrium of earth conductivity and spatial current distribution when calculating GICs in large-scale power grids. (6) The monitoring technology of GICs in power grids is investigated,and a monitoring devlce,for which National Patent is authorized,has been developed.The devices can monitor not only GIC but operating parameters of transformers under the effects of GICs.The experiment result shows that functions and performance of monitoring devices meet all design requirements.Nowadays,GIC monitoring devices have been installed and operating in many substations and constitute a GIC monitoring system of power grids.