Probabilistic load flow method considering branch outages

This paper proposes a probabilistic load flow (PLF) method considering random branch outages as well as uncertainties of nodal power injections. Branch outages are simulated by suitable power injections at corresponding nodes. Fluctuation of loads and unscheduled unit outages are all considered as disturbances of nodal power injections. Linearization formulation of power flow equations are employed to solve the variations of state variables under these uncertainties. To reduce the error raised by linearization, deterministic power flow is run under those discrete disturbances which have considerable influences to the system. To obtain the cumulants of the distributions of nodal voltages and branch powers, continuous and discrete distribution parts are calculated respectively. The discrete distribution is solved by the method proposed by Von Mises based on moments. The distribution functions of nodal voltages and branch powers are found by convoluting their discretely and normally distributed part. Influence of branch outages to the results is analyzed through a case study of the RTS 24-node system. Tests show that the proposed PLF method can obtain similar results as Monte Carlo simulation method with much higher speed. An application of the proposed PLF method to a practical system is also given to show usefulness of the proposed method.