Risk Assessment Methods And Countermeasures Of Power Grid Under Ice-Covered Disasters

With the rapid development of society and economy,modern grid structure is becoming more and more complex.Long distance and large capacity transmission lines are increasing,most of them are directly exposed to natural environment.They are very vulnerable to natural disasters or extreme weather and bring safety problems to the power grid.The natural disasters that have the greatest and widest range impact on the grid are frozen disters.Severe ice disasters may cause a large-scale grid blackout or even the power system failture.Therefore,it is of great significance to carry out research on the risk assessment methods and countermeasures of ice-covered power grid in conjunction with the climate information during the ice disaster and the operation conditions of power grid to improve the ability of power grid to respond to extreme weather.In this context,this paper first presents a time-varying failure probability calculation method for transmission lines under icing.This method analyzes the interaction of ice thickness and wind speed on transmission lines through the ice growth forecast model and then proposes a calculation model of ice and wind load.From the perspective of mechanics,this method proposes the theory of time-varying reliability of transmission lines based on the interference theory of stress and strength.Then this method combines the influence of ice and wind load to propose a time-varing failure probability model for transmission lines under ice disaster weather,realizing real-time calculation or prediction of the failure probability of ice-covered lines.Secondly,this paper constructs a quantitative evaluation index that can reflect the security and stability of system.The index assesses the vulnerability of power grid from both static and transient perspectives.A set of quantitative evaluation method for offline safety and stability of power grid under icing is also proposed in this paper.Combiling with the fault probability of lines,the expected failure set is obtained to calculate the total risk level of system.Then for high-risk system,this paper proposes a set of reasonable and feasible methods for formulating ice melting programs to maxmize the stability of high-risk system.Taking the new England system and the Hunan power grid as examples,the offline safety and stability assessment process of power grid under ice covering is detailed.Finally,this paper proposes a complete set of online risk assessment and response measures for ice-covered power grid.The method utilizes EEAC theory for calculating the stability margin of system to judge the stability of system,and then formulates the emergency control strategy based on the minimum cut amount that satisfies the system stability.The effectiveness of the method is validated with the new England system.