Quantitative Evaluation Of Fault Criticality On Power System Transient Stability

With the implementation of China’s "West-East electricity transmission project,exchange electric power between South and North,interconnection in the whole country" energy strategy,the gradual deepening of power market establishment,the steady development of smart grid and energy Internet construction and the successful operation of "eight alternative and eight direct" Ultra High Voltage transmission project,the AC-DC interconnected power grid in China has become the world’s largest in scale and highest in voltage level,and provides strong power security for China’s economic and social development.At the same time the development of AC/DC hybrid power system,the integration of large scale renewable energy and the mass application of power electronic equipment,the dynamic characteristics of power system in China has changed in nature.The interconnected power grid transmission being large in capacity,long in distance system,complicated and changeable in system operation modes and fault scenario causes the danger of developing systematic cascading outages from small local fault ever increasing,which makes the security operation of the system face severe challenges.The hidden danger in the stability of interconnected power grid threatens the security and stable operation of power system.The blackouts caused by system instability will impact immeasurable losses on the society and economy.Power system fault criticality is the expansion of the existing concept stability margin.The difference is that power system stability margin is comparing the post-fault system to the critical stable condition,and the emphasis lies in the system;while fault criticality is comparing post-fault system to normal operation conditions,and it unites fault with the security of system.The relationship between quantities of power system first defending line and the second defending line can be established through the quantitative description of the fault criticality degree.The innovation point of this paper is to put forward the concept of the fault criticality degree and its quantitative analysis is carried out.First,the existing security and stability methods are deduced theoretically,and their characteristics and shortcomings are analyzed.With some improvement of existing methods,the analysis method in this paper is determined.The generators group identification after the occurrence of fault in power system is studied.This paper takes the generator power angle information as sample,considering the network topology,fault type,fault location,power system operating conditions,using the corrected principal component analysis,based on that the network is equivalent to two group swing models.After group identification is performed,the energy function is used to establish the quantitative degree index of the generators to evaluate the impact of fault on the power system.First of all,transformation is carried out on the grouping generators and system model is simplified;then aiming at the shortcomings of lacking in precision and loss of physical meaning,the energy function is utilized to analyze the unstable energy produced in each part of system,finally it is applied to power system fault criticality quantitative assessment.Considering every detail,easy to implement and low computation is the advantages of proposed method,therefore it is expected to be applied to real-time transient stability margin assessment.Finally,the feasibility and effectiveness of the proposed method are verified by the simulation study on the IEEE 4-machine two-area test system and 16-machine systems.