Power System Risk Assessment Considering Extreme Weather Events

With the development of the economy and society in recent years,the natural environment has suffered more and more serious damage.Abnormal weather,especially extreme weather,occurs frequently around the world,such as extreme ice and snow,storms,and continuous hot weather.As the most complex man-made system in the world,power system distributes in wide area.Most of the power equipment is directly exposed to the external environment,especially transmission lines.Therefore,the power grid is easily directly affected by external environment.The ice accumulated in transmission lines in extreme ice and snow weather can lead to line breaking,tower falling or other faults.Strong wind can directly cause mechanical damage to the grid equipment or result in line galloping.The main research method of extreme meteorological influence on power grid is the sampling based on the failure rate related with extreme weather and statistics of simulation results.In the method,the dynamic processes between the two systems is reveled not enough.Furthermore,the relationship between the severity of extreme weather events and the failure rate is assumed without enough research.Extreme meteorological events are characterized by low probability and serious consequences which will cause faults in power grid with clustering and cascading characteristics.Traditional reliability assessment methods can't satisfy the assessment requirements.A hybrid simulation framework considering the dynamic processes of meteorological systems and power systems is established in our research.Furthermore,a risk assessment method based on the results of hybrid simulation is proposed.The detailed research results are as follows:(1)The mechanism of ice accretion on transmission lines with extreme ice and snow weather conditions is analyzed and the factors affecting ice accretion process are summarized including temperature,precipitation,wind speed,wind direction and thermal effects of current.Transmission lines are affected by extreme icing weather events as following:line breaking or tower falling out of ice overweight on transmission lines;flashover of ice-covered insulators out of operation voltage;low-frequency and large-amplitude self-excited vibration of transmission lines out of wind effect;mechanical accidents caused by icing or de-icing of different period is adjacent lines.The mechanism of line galloping is summarized,and factors affecting line galloping is analyzed including the effect of line ice accretion,wind speed,wind direction,line structure and parameters.The characteristics of line galloping are summarized based on large numbers of historical line galloping accidents.(2)The interaction mechanism between ice accretion dynamic process and power system is researched based on the model of ice accretion on transmission lines considering thermal effect of current.In the research,the long time scale and clustering characteristics of cascading faults is analyzed.A numerical simulation method and framework of hybrid simulation of power systems considering extreme ice weather events is established based on the characteristics of power system faults with extreme snow and ice conditions.In the hybrid simulation process,the impact of ice accretion events on power grid topology is considered,and the effect of power system power flow transferring on ice accretion is also contained.Furthermore,the ice accretion process of meteorological system,the transient process after fault in power system,power flow updating without faults are realized.Based on the power system electro-mechanical transient simulation software PSS/E,an extended software simulation package considering both power system and meteorological system is developed.The numerical simulation results also prove the efficiency of hybrid simulation,which extends power system simulation function greatly.The simulation of the dynamic processes considering the two systems in different time scales with high efficiency provide operators guide of meteorological and power systems.(3)The hybrid simulation framework considering line galloping and dynamic process of power system is established to reflect the fault characteristics of random clustering cascading faults of long time scale caused by line galloping.In the framework,the dynamic effect mechanism is reveled.The relationship between line galloping amplitude and line faults rate is constructed with modeling method.The random characteristic of line galloping is reflected by the sampling of fault rate results.A hybrid simulation platform of power system considering line dancing is established.The interaction mechanism of line dancing and dynamic process of power system is revealed in the platform.The simulation reflects the characteristics of line galloping,such as long-time scale,clustering and cascading.Based on the simulation software,simulation cases are verified,and the line galloping events simulation interface expansion package based on PSS/E is developed.Based on the simulation platform,the problem of large differences in time scale between line dancing and transient process of power system is solved.The concept and function of current power system simulation is extended greatly through the simulation framework and platform.(4)An assessment method to evaluate the impact of extreme weather on the power system is proposed based on the hybrid simulation platform which considers extreme snow and wind weather.A hybrid simulation meteorological-electric power system platform considering both ice and wind weather is developed to reveal the dynamic process of extreme weather events that threaten the power system and provide a large amount of data for further study.Based on the results of the hybrid simulation platform,a risk assessment method and a comprehensive evaluation index are proposed to reflect the characteristics of the power system faults under extreme weather conditions.The impact of extreme weather on power grid can be assessed with the proposed risk assessment index quantitatively.A system including ice-wind hybrid simulation and risk assessment is developed to provide information support to relevant power system operators.