Research On Risk Assessment Of Power Grid Transmission-line Trips Due To Wildfire Disasters

In recent years,with the increase of loads and the development of power grid,expansion of power grids in China have been expanded constantly,especially with the mature development of UHV technology,large-capacity and long-distance trans-regional transmission lines have been continuously put into use,transmission-line corridor gradually extends to the areas where wildfires frequently occur,problems caused by wildfires have become more and more evident.Every year in wildfire high-occurrence seasons,transmission lines trip more or less due to wildfires,and in most cases,reclosures of transmission lines fail.Characteristics of wildfires include wide spread area and intensive outbreak time,which may cause cascading tripping failure of multiple transmission lines in one area,the consequent impact on power grids will affect their safe and stable operation,cause the formation of power grid imbalanced structure,reduce the reliability of power supply,and even lead to large-scale outage of transmission lines,eventually result in udden blackouts in large areas,threatening the normal operation of the power system.It can be said that wildfire has become one of the most important reasons for the trip and outage of transmission lines.In order to reduce the risk of power grid faults caused by wildfires,improve the efficiency and accuracy of wildfire prevention and control,and specify the power grid fault emergency disposal strategy in time and effectively,this paper is based on the identification technology of fire spot dynamic brightness temperature threshold and the triple nested meteorological numerical calculation model as well as the analysis method of power grid security and stability,with the probability calculation of power transmission line tripping under wildfire conditions and the critical analysis of power grid transmission-line are considered,this paper focuses on power grid transmission line tripping risk assessment methods and countermeasures under wildfire disasters.The main research contents are as follows:(1)Studied the disaster failure mechanism,disaster model and prevention measures of various typical power grid natural disasters,analyzed disaster-causing factors and typical characteristics of various disasters;on this basis,elaborated the basic theory of power grid disaster risk assessment,including how to define and express risks,how to manage power grid fault risk according to the characteristics of disasters;finally,introduced the power grid disaster early warning technology and disaster fault response and prevention measures,which is able to be used as emergency treatment guidance for power grid fault caused by sudden natural disasters.The basic theory research on power grid natural disaster risk and prevention helps to understand the relationship between natural disaster and power grid fault risk.It is the theoretical basis for the cross-disciplinary research of electrics,meteorology,physics,chemistry and other disciplines.It has important guiding significance for the follow-up study of power grid fault risk assessment under wildfire disasters.(2)By virtue of the test conditions and measurement advantages of the actual large-capacity transmission line wildfire trip test site,the test data of the transmission line trip due to wildfire conditions was analyzed statistically,and the influence of temperature,particle as well as electron concentration and ion concentration on gap breakdown was discussed.Then,the discharge mechanism of transmission line under wildfire condition was discussed considering comprehensive analysis on various factors,and the model of gap discharge under wildfire condition was put forward.Based on a large number of historical statistical data,the temporal and spatial(geographic)distribution of wildfires were summarized,and the relationship between the high incidence period of wildfires and human activities was discussed.Based on wildfire spot grid density prediction algorithm,an early warning method on transmission-line wildfire disaster was proposed to realize wildfire quantitative prediction of transmission-line corridors.(3)Considering the existing fire monitoring methods are unable to obtain wide-area fire points and micro-scale meteorology data of the micro-topography area near the transmission lines in real-time,thus cannot accurately calculate the trip risk of transmission lines due to wildfires in real-time,a real-time analysis approach for transmission-line trip risk considering wildfire disaster was proposed.First of all,a dynamic threshold fire-point identify method for small size wildfires based on synchronous satellite was presented,and then a meso-micro scale weather forecast method of multi-nested mesh model was put forward to solve the conflicts between numerical accuracy and tide timeliness,also,a real-time transmission-line trip risk analysis approach which considers various environmental factors such as precipitation,vegetation and wind was proposed.Finally,the approach was applied to a high incidence period of wildfires in Hunan province as a case study,the analysis results show that the proposed approach can effectively analyze the trip risk of transmission-lines due to wildfires in real-time,and also provide supportive data to the safe operation and emergency disposal of power grids under circumstance of large scale wildfires.(4)Considering the existing key transmission-line evaluation methods normally base on singular factor or Subjective selected factors,thus unable to evaluate the key transmission-line under large-scale wildfires comprehensively and reasonably,a Super Efficiency Data Envelopment Analysis Based Key Transmission-line Aggregate Evaluation Method was presented.This method considered both static operation status and line tripping influence of transmission-lines,and established factors for both two sides,then,proposed a new comprehensive key transmission-line evaluation method with multiple factors.We applied the method to a power grid in a wildfire-prone region,the test result showed that the method identified the key transmission-line rapidly and effectively,thus to provide auxiliary decision guidance for the safe operation of the power grid.(5)Through the overall analysis of the probability of transmission-line tripping due to wildfires and the importance of transmission lines in power grids,a risk assessment method for transmission-line tripping under large-scale mountain fire hazards was proposed.On this basis,based on the principle of game theory,the fault risk was taken as payment function,the reply strategy for power grid wildfire fault was made,so as to provide countermeasures which were able to reduce the risk to the lowest level.Under the guidance of this strategy,from the emergency disposal and active prevention perspectives,a wildfire emergency disposal method based on fire dynamic threshold identification and a load transfer strategy based on demand response technology were proposed.The results showed that the above methods were able to effectively quantify the impact of wildfire disasters on power grid safety and stability,optimize the distribution of wildfire prevention resourses,improve the load curve of power grid,fundamentally reduce the risk of power grid wildfire disasters.and ensure the safe and stable operation of power grid.