Study On Safety Assessment And Early Warning Technology Of Transmission Network Considering Icing Disaster

As the size of the power system is relatively large,usually boast a number of areas for energy transmission,it has been attacked by various natural disasters.Especially,the icing of the power grid in recent years brings serious damage to the stable operation of the power system.In view of the influence of icing disaster on the transmission network,the thesis studies the safety and stability evaluation and early warning technology of transmission network.In order to predict the icing density,an extreme learning machine is proposed to solve the problem that the icing density varies with the weather.In order to predict the ice growth of transmission lines,based on the existing.ice growth model,firstly it is considered that the increase in icing is related to the diameter,which in turn is increasing with icing growth,secondly,the semi surface area is used as the contact area with air,and finally,a general model for the calculation of the growth of various types of ice accretion is established.According to the amount of ice to get the stress suffered by the conductor,aiming at the influence of aging failure on the fault probability,this thesis presents a method to calculate the fatigue damage coefficient of the transmission line by using the service age regression factor.And the exponential function is used to fit the fault probability of broken line,dancing,falling tower and flashover,under the assumption that all kinds of faults can cause the circuit breaker to trip correctly,the final result of all kinds of faults is regarded as line break.Static security analysis and voltage stability analysis of the power network which is tripped by the fault of the wire break;this thesis is based on the traditional method of N-1 contingency set selection.And the real time probability of line breaking is considered.On the analysis of static security analysis and static voltage stability,the risk screening index is put forward.It can not only reflect the size of the fault of the circuit,but also can reflect the severity of the static security and voltage stability.In view of the actual circuit breaker may refuse to move,the false move,as well as in the analysis static security and the voltage stability hypothesis has made the circuit breaker to trip correctly this situation,after proposing six indexes of static safety and voltage stability,three safety checking indexes are put forward.In this thesis,the establishment of nine indicators,the use of multi-level fuzzy comprehensive evaluation of security and stability assessment;In order to determine the weight,the entropy weight method is used to determine the weight of each indicator.For the criterion layer,the weight of the index is determined by the improved 3-level analytic hierarchy process.Finally,the safety and stability indexes of the transmission network under ice disaster are obtained,and the warning level is judged.By using RBF neural network to predict the safety and stability of power grid in the future period is proposed,the time sequence diagram of security and stability is obtained,which can reflect the stable trend of power network.The safety assessment and early warning software system for icing network is developed.This thesis chooses the transmission network with 11 nodes of 9 nodes in Liaoning as an example,and the results are verified by software.