Research Of Risk Assessment And Online Early Warning Of Power Grid Fault Under Extreme Weather

In recent years,frequent typhoons and heavy rains have severely affected the normal operation of the power grid by damaging power equipment.There are many factors involved in equipment failure under disaster weather,the disaster-causing mechanisms and disaster-causing methods of different disasters are quite different.How to build a failure probability prediction model,integrating weather forecast information with power grid fault information for the online early-warning is very challenging.In addition,the power system changes rapidly under disaster weather.How to conduct online risk assessment and ensure the timeliness of risk results has become the research focus of the power industry.This paper mainly carried out the following specific work on the above issues:(1)In view of the problem that strong typhoon can cause low-cycle fatigue damage to transmission towers throughout the impacted area and initiate tower collapse,leading blackout to power system,an early warning method of transmission tower considering plastic fatigue damage under typhoon weather is proposed.Firstly,a typhoon warning start point(TWSP)is selected to ensure prediction accuracy of transmission tower failure probability and timeliness of personnel and materials deployment for power companies,then mesh generation is applied to determine the risky tower affected by typhoon at TWSP.Secondly,duration time and changing wind speed of typhoon on risky tower are calculated according to typhoon short-time forecast information at TWSP,and the wind speed is revised in the light of microtopography.Finally,the low-cycle fatigue damage mathematical model based on fatigue damage theory is combined with the improved Poisson formula to attain the failure probability of the transmission towers.In addition,since typhoon develops and dissipates with time,the typhoon path is tracked to correct the low-cycle fatigue damage value on the basis of typhoon nowcasting information,and the failure probability of transmission towers are constantly updated until typhoon departs from the risky zone.(2)In view of the problem that the environment around transmission lines in mountainous and hilly areas is complicated,rainfall-induced landslide may cause transmission towers fault and influence the safe and stable operation of power system,an early-warning method of transmission tower fault under rainfall-induced landslide disaster is proposed,which achieves the quantitative online early-warning of the entire disaster process from aspects of landslide risk area,landslide activity time and damaged condition of transmission tower.Firstly,the target risky area is obtained by overlaying the rainfall forecast area and grid area with GIS technology,and the landslide area is determined with grid-based landslide disaster index.Secondly,the daily variation of rainfall infiltrating into the soil is analyzed combined with meteorological data,and a dynamic updating cumulative effective rainfall model is established,and then a landslide probability model which could predict landslide activity time is presented.Finally,the quantitative function relationship which reflect damage degree of transmission tower is obtained from work-energy aspect,with the impact force of landslide as disaster-causing intensity while the deformation energy which is relative to the maximum deflection as disaster resistance.(3)In view of the problem that the traditional offline risk assessment method is not suitable for disaster weather with changing meteorology in short-term,an online risk analysis method of transmission line failure under typhoon and heavy rain disaster is proposed.The minimum load loss is used as failure consequence in the method,avoiding the difficulty of estimating power outage loss and control cost under disaster weather in a short time.After integrating the failure rate under typhoon disaster and heavy rain disaster with the principle of independent events to obtain the transmission tower failure rate,the series reliability formula is used to calculate the transmission line failure probability,the system failure states are generated on this basis.Combined with the characteristics of the short-time forecast and nowcasting,an adaptive contingency screening method is put forward.A basic fault set requiring power flow calculation and an anticipated fault set with consequences of load loss under short-time forecast are generated.On the basis a preselected fault set is generated by adaptive screening the fault state,the real-time,effectiveness and rapidity of online risk assessment is ensured by improving the efficiency of generating and analyzing preselected fault sets.In summary,the online early warning and risk analysis methods for typhoons and heavy rain disasters proposed in this paper are helpful for dispatchera to grasp the evolution of the disaster accurately,and provide guidance for power companies to make dispatch control decisions.