Probabilistic Assessment Of Static Security And Voltage Stability Of Power Systems

Because of the uncertainties of load forecasts and the uncertainties of the generation power injections created by the deregulated power market, the study on probabilistic security assessment is going to be more and more important. This paper presents a method to calculate the probability of system static insecurity and voltage instability by using the Stochastic Load Flow (SLF) and the Cut-Set Voltage Stability Region methods. Based on Newton-Raphson load flow calculation and the concept of Cumulants and Gram-Charlier expansion theory, we can easily obtain probabilistic distribution functions and probability values of the variables of interest, and significantly reduce the computation burden of the process of convolution.Given the network topology and forcasted operating condition, including power injection of loads and generators, we can easily calculate not only the static insecurity and voltage instability probability of the whole system but also the detailed probability indices of each of the bus voltages and of each of the line power flows. And critical node injections can be found by comparision and sensitivity analysis. Given the selected contingencies and their corresponding failure rates, the total probability of system static insecurity and voltage instability and the contribution of each contingency to probability of system insecurity can be obtained.The program based on this method has been developed in FORTRAN-77 language, which has been successfully applied in calculating the probability indices of New England 39-bus test system. It is shown that both accuracy and efficiency of the method are acceptable in real time security assessment of power system to assist operators make decisions of preventive control and emergency preparation.