Research On Key Technologies Of Operational Risk Assessment For Power Transmission And Transformation Equipment Of Urban Power Grid

Urban power grid is the bridge between large power grid and power consumers.With the continuous development of social economy,urban power grid faces more and more potential risk under the condition that urban power grid grows larger and the structure is more complex.The risk identification,monitoring and control based on the online operational risk assessment have been paid much attention for the security and reliability and become one of the central tasks of urban power grid operation and management.Urban power grid contains a large number of power transmission and transformation equipment.Due to the large number of equipment,the complicated stochastic factors,and the coupling effect of different equipment combinations on the power grid,it is difficult for the operational risk assessment and many theories and technical issues need to be solved.The key technologies of urban power grid operational risk assessment are researched in this dissertation combined with National High-tech R&D Program(863 Program).And it is of great theoretical and practical significance for the key technologies to improve the level of security and reliability and promote the engineering application of online risk assessment.The main purpose of power grid operational risk assessment is to identify and monitor the contingencies,and to provide decision-making for risk control.Based on the objectives above,the overall design scheme which contains data layer,risk assessment function layer and presentation layer,is proposed.Firstly,the data requirements,data sources and data conversion methods are described in the overall design scheme.Secondly,the function and calculation process of each module are explained.Thirdly,the contents and methods of operational risk assessment are presented combined with the actual needs of the operation site.A reasonable risk assessment index system is an important basis for risk assessment.Firstly,combined with the structural and operational characteristics of urban power grid,a risk index hierarchy including load loss,grid structure integrity,equipment loss and grid security margin,is proposed based on the construction principle.Then the calculation methods of each index are given,including the definition and formula.Finally,according to the index result,the grading method of risk severity is presented.In order to solve the issues of low calculating efficiency and long calculating time by anticipated multi-contingencies in the operational risk assessment,an anticipated risk contingencies selection method based on fault influence range is proposed.This dissertation puts forward the method of fault influence range,and selects the primary results by the interaction of fault influence range.Then topology analysis and power flow calculation are adopted to verify the topological analysis results and violation of primary selection results,and the contingencies of splitting and violation are classified into the final set of risk scenarios.The simulation results show that the proposed method can significantly improve the identification speed of multiple(N-2)fault risk scenarios,and meet the application requirements of online risk assessment better.Load loss caused by the failure of power transmission and transformation equipment is significant for risk consequences,and is also one of the core contents of power grid operational risk assessment.In order to solve the problem that the traditional load shedding model based on global optimization has a large amount of computation,a new method of load shedding based on sensitivity analysis is proposed.The sensitivity analysis is presented to determine the load shedding range,which converts global optimization into local optimization to reduce the dimension of load shedding model and improve the computation efficiency.The good performance of the proposed method is verified through a simulation example.Combined with the requirements of engineering applications,the software module is designed and developed based on the theoretical research above,and the correctness of the software design and the theoretical method are verified through an example.In the end,the whole works of this thesis are summarized and the future prospect on the development of operational risk assessment of urban power grid is highlighted.