Modeling And Evaluation Of Resilience Power Grid Under Extreme Space Weather

The process of solar activity produces a stream of charged particles radiating outward with enormous energy,forming the solar wind.The solar wind’s interplanetary propagation extends the solar magnetic field,causing disturbances to the magnetosphere-ionosphere and causing magnetic storms that cause dramatic changes in the magnetic field.Geomagnetically induced current(GIC)is generated driven by electric fields on the earth’s surface.Because there are connection points between the transformer and the earth GIC will flow into the transformer through the neutral point and circulate in the closed loop between the power system and the earth,resulting in increased reactive power loss and strong temperature rise of the transformer.Once the GIC inflow exceeds the maximum allowable value of the transformer,the failure will most likely cause the transformer to withdraw from operation,and then a chain fault occurs,which menaces the transformer’s stable operation.Firstly,by analyzing the influence mechanism of GIC on the transformer,a coupling model of magnetic field and temperature field of three-phase five-column transformer of 500kV was constructed.The transformer’s magnetic field and temperature field changes under different DC conditions were analyzed and compared by applying excitation from external circuit.The results show that:GIC can cause uneven distribution of transformer flux,and the magnetic flux of the middle main column is significantly higher than that of the two main columns.The GIC will cause the temperature of the transformer’s iron core and winding to rise significantly,and the winding temperature rise is significantly higher than that of the iron core.Under the size of the 50A GIC,the temperature rise has obviously exceeded the safety threshold.In view of the above effects,three commonly used GIC suppression measures are summarized and proposed,including resistive GIC treatment device,capacitive GIC treatment device,reverse current injection at the neutral point of a transformer,which can effectively prevent GIC from the source and avoid a series of adverse reactions.Secondly,the transmission reliability test system IEEE-RTS-79,which contains 24 nodes and 38 lines,is selected as an example.Combined with relevant parameters and the WGS84 earth model,the geographical location in Shandong Province was obtained to study the Shandong Province’s resilience power grid.The power system’s equivalent model under GIC is constructed,and the GIC calculation model of the system is simplified and constructed.The GIC level under uniform ground electric field is calculated and analyzed,including the GIC amplitude and the GIC reactive power loss.The results show that the single-phase GIC size of more than half of the nodes exceeds the maximum allowable DC current size specified by the standard under the uniform ground electric field of 1 V/km,and the GIC reactive power loss is linearly correlated with the GIC amplitude.Then,statistical tools were used to standardize the GIC size and obtain the relative vulnerability index of the system.It was found that 6 nodes are vulnerable nodes.Based on the GIC level,combined with the corresponding criteria and statistical methods,the initial failure probability model of the node under GIC was constructed.By using the non-sequential Monte Carlo method and the fault model,the random initial fault nodes are obtained and the random initial fault situation is simulated.Finally,the resilience grid under GIC is constructed.This paper presents a method to evaluate the elasticity of transmission system based on GIC events,and selects the system loss performance under GIC as the evaluation index.The optimal DC power flow model is established under GIC.On this basis,considering GIC strength,recovery resources,geographical location and repair team,a recovery model under GIC is constructed.Topological structure is used to generate fault recovery order,and the recovery order is optimized by genetic algorithm.According to the transformer characteristics and recovery model,a variety of resilience lifting strategies are proposed,such as improving the recovery efficiency and improving the transformer GIC tolerance level.The resilience indicator under different strategies are analyzed to verify the effectiveness of different resilience lifting strategies,providing a reference for the rapid recovery after GIC.In summary,this paper studies the influence of GIC on transformer and power system,simulates and analyzes the changes of 500kV transformer under different GIC,and builds the equivalent calculation model of GIC and the resilience power grid model for GIC.The research content of this paper can provide basis and reference for GIC prediction and prevention,recognition of vulnerable nodes of power system and fault recovery of power system under GIC.