Research On Early Warning Mechanism Of Power System Cascading Failures Based On Critical Phase Transition

Interconnected power grid improves the economy and operational reliability, brings tremendous social and economic benefits, but also increases the risk of local failure causing blackouts. In particular, in order to pursue higher economic efficiency, the construction of modern power systems tends to be large-capacity units, high-capacity transmission line, running tends to limit; in order to achieve sustainable energy development, large-scale intermittent energy such as wind power/photovoltaic power accessing grid brings greater uncertainty, which presents new challenges to the reliability of the power system. Research on cascading failure prevention and intervention is very important to prevent the occurrence of blackout so as to maximum reduce the economic losses and social unrest. The research on cascading failure prevention and intervention mainly focuses on the specific failure mode and whether causes chain reaction, but with the expanding of the power grid, there is a problem of combinatorial explosion. Based on the theory of phase transition, this article focuses on the operation state which is running from safe state to critical state to study the early warning of cascading failures.The main contents of this paper are as follows:(1)In-depth understand critical phase transition and review the research status of flickering and critical slowing down which are the main early warning signals in different areas.(2)The OPA model is improved by neglecting the long-term process of generator and line expansion to establish critical phase transition analysis model. The model simulates the increase of the system operating pressures by simulating the load continuous growth. The flow and outage data are obtained by simulating under different operating state. From a macro perspective, the characteristic of the system during the evolution of the critical is studied.(3)Based on the theory of critical transition, this paper chooses the autocorrelation coefficient, skewness and variance of the line average load rate as main study object to establish the early warning indicator system for the power system critical phase transition. Simulation results with IEEE-30 bus test system are used to verify the effectiveness of the index system of the critical phase transition and analyze the effect of the choice of calculation parameters on the results stability.(4)Based on the main characteristics of cascading failures, this article establishes the critical phase transition risk indicators: EENS, the size and its occurrence probability and equilibrium entropy. Based on the operating characteristics of lines, this article establishes the indictors of critical reason: load rate, the average load rate, the equivalent transmission limit and the equivalent transmission capacity. Simulation results with IEEE-30 bus test system can analyze the effect of the operating parameters on the risk of critical phase transition, get the variation characteristics of the line in the process of closing to the critical state and identify the critical vulnerable domain of the system.