Security Region Based Probabilistic Security And Risk Assessment For Power Transmission System

Since uncertainties in a deregulated power system have put forward great challenges to traditional deterministic security assessment, security region based probabilistic dynamic and static security and risk assessment approaches are developed in this dissertation.Firstly, a practical dynamic security region (PDSR) based transmission system probabilistic dynamic security assessment model is developed combining discrete and continuous stochastic variables in this dissertation. In this model, not only the uncertainties in loads and generation power injections, probabilities of critical contingencies, uncertainties of fault occurrence locations, uncertainties of the fault-clearing time but also uncertainties of load model in stability analysis are considered. The hyperplane mathematic descriptions of PDSR make it easy to take account of the uncertainties of power injections and the uncertainty of motor loads proportion in total load, and can outstandingly reduce computation burden of dynamic insecurity probability. Furthermore, supposing that power injections follow truncated normal distribution, a method of Gram-Charlier progression based on cumulants is adopted to calculate the joint probabilistic distribution of truncated normal distribution, which is more up to the reality.A probabilistic steady voltage stability security assessment model based on stochastic load flow (SLF) and static voltage stability region in cut-set space (CVSR) is presented. The probabilistic distribution functions (PDFs) are obtained by SLF based on Newton-Raphson linear method. Then, the PDFs of linear combination of line flows in CVSR are deduced by Gram-Charlier progression and Cumulants. The probability of static voltage instability can be calculated by hyperplane equation of CVSR.This dissertation presents a dynamic insecurity risk assessment model based on practical dynamic security region. The influence of security control methods applied to transmission system is considered in the calculation of dynamic insecurity risk, and the transient stability constraints can be considered easily by an inequality in form of hyperplane. A risk control optimization model is given taking total risk cost as the objective function. The optimization model can be divided into two layers. The outer layer is contingency set optimization while the inner is an optimization problem of comprehensive security control cost to a given subset of contingency set. Finally, based on the theory of probabilistic security assessment stated above, an online probabilistic security assessment system for transmission systems is developed by our research group for a real power system in our country. The system provides the insecurity probability in the future up to several hours. By sensitivity analysis, the information, such as faults making the most contribution to the system insecurity probability and nodes influencing static voltage insecurity probability outstandingly, can be obtained. The system can be used to guide operators to decide whether it needs to take preventive control actions and the optimal comprehensive control actions that can be taken to keep system security degree in a relatively high level according to the state of power system.