Research On Meteorological Disaster Risk Analysis And Fault Early Warning Methods For Overhead Transmission Lines

Large quantities of overhead transmission lines and other transmission and transformation equipment are exposed to meteorological environment for a long-term, consequently, their safety operation directly influences the security of power systems. Years of operation experience on power systems reveal that transmission equipment failure caused by external meteorological environment is one of the most significant influence factors of power system security. In the context of climate change, there exists an increasing trend in the frequency and intensity of adverse weather and extreme climatic events. How to deal with meteorological disasters is one of the ineluctable key problems for power systems. Research on meteorological disaster early warning, risk prevention and control theory and technology have become long-term hot research issues in the field of electrical engineering.Abundant security technologies have been obtained to deal with the impact of meteorological environment as the development of power systems. Taking advantage of many years’ observation data and the results of mechanism analysis on meteorological disasters, protection and defense measures have been taken into consideration when designing the structure and insulation of transmission line. Unfortunately, transmission line faults and trip-out events caused by adverse weather are still happening frequently, as well as the risk of large area blackout accident still exists. This shows that our knowledge about meteorological risk on power system is still not enough. Current security protection theory and technology based on the static state and equipment level cannot meet the needs of the safety operation of power systems. Online dynamic risk identification, prevention and control measures are the important approaches to improve the overall risk prevention and control of power systems.With the development of the weather observation and weather forecast technology, the spatial and temporal scales of predicting meteorological events are greatly reduced. Refined weather forecasting has become a significant impetus and safeguard of meteorological risk control and management for power systems.Currently, when analyzing the influence of meteorological factors on power grid, the temporal scale is always treated as average of many years and the spatial scale is always determined according to the accumulation experience in regions, and quantifying meteorological risk lacks detailed parameters. Meteorological risk management and control of power systems still lack accurate methods and mathematic models for risk early warning. We can only make a pre-arranged planning to defense large scale meteorological trend, but cannot adjust operation mode in time or take corresponding emergency disposal for a particular weather process.For these reasons, the goal of this dissertation is to construct the theoretical system of refined meteorological risk analysis and early warning for transmission lines. Start from diminishing the temporal and spatial scales of meteorological risk analysis, establish the characteristic index and model of meteorological risk delicate analysis for transmission lines. From the mechanism regularity and statistic characteristics of meteorological disasters impacting on transmission lines, build online risk early warning methods for typical meteorological disasters. The main works of this dissertation are as follows:a) The influence patterns of meteorological factors on transmission lines are concluded, the meteorological-related fault event statistical characteristics of transmission lines are analyzed, the idea of description transmission line meteorological risk is proposed, the representation method of transmission line meteorological risk is given, the risk prevention and control approach of power grid based on weather information is proposed, and the method of constructing the meteorological risk early warning system for power grid is proposed.b) In order to establish the the complete description indices for transmission line meteorological risk, the description methods of meteorological-related transmission line risk based on fault space-time characteristics are proposed. The index parameters such as meteorological sensitivity, high risk section, fault time interval, and MTTR under different meteorological disasters are proposed, the influences of meteorological disasters on the transmission lines are concluded into three elements of geographic location, time period, and main composition to build the statistical description method of transmission line meteorological risk. They can reflect the temporal characteristics and sensitive meteorological factors of transmission line meteorological risk, and provide practical decision-making information for planning, operation, and maintenance of power systems. Transmission line fault samples of a provincial power grid have been taken as examples, and the evaluation results show that the proposed methods and indexes are valid and superior.c) For the issue of lacking time-varying fault regularity mathematic models for transmission lines, a meteorological-related failure rate model with continuous time is proposed. The time-dependent failure rate model and probability distributions of forced outage time under different meteorological disasters for transmission lines are built through adopting Fourier, Gaussian, and Weibull functions to simulate the time distribution function base on failure rate samples of transmission lines. It can provide favorable conditions for implementation of meteorological risk early warning and risk prevention for transmission lines. The parameters of these functions are fitted and compared using the fault samples of a province power grid and an urban power grid in China. Results show that the proposed simulation models are reasonable.d) For the early warning issue of wind swing discharge caused by strong wind, a probabilistic early warning method of wind swing discharge is proposed through treating it as a problem of comparison and prediction with uncertain inputs. The influences of wind forecast accuracy on the prediction of the swing angle are analyzed. The probability distributions of forecast wind direction angle and wind speed are established based on the prior distribution of wind forecast accuracy. The wind swing angle is calculated based on wind direction and wind speed samples through Monte Carlo simulation. The calculated swing angle is then compared with the designed maximum swing angle of the suspension insulator string to realize the probabilistic early warning of wind swing discharge for overhead transmission lines under short-range wind forecasts. The proposed method is verified with a practical example.e) For the early warning issue of conductor galloping in ice covered regions, an early warning method for transmission line galloping based on SVM and AdaBoost bi-level classifiers are proposed through treating it as a problem of classification and prediction under supervised learning. A prediction model of apt-galloping weather conditions based on an SVM classifier is built through data mining of historical weather parameters in regions where galloping events frequently occurred. When the forecast weather conditions of a particular region satisfy the apt-galloping weather conditions, the conductor type, cross section and span of transmission lines that pass through this region are considered to realize early warning of galloping through an AdaBoost classifier. The historical galloping events of Henan power grid are adopted to verify the validity of the proposed methods.In view of the contradiction between the random feature of meteorological process and the deterministic demand of online fault defense, both the indexing risk description methods to reflect the random process and continuous time fault risk models are established, which can meet the needs of systematic risk assessment and risk prevention in a particular process. The proposed meteorological disaster risk early warning methods and models can help to promote the development of the theory and technology about online meteorological risk prevention and control for power systems.