Development of a hybrid type assessment method for power system dynamic reliability

The decision of the optimum scheme for preventing fault cascading is one of the most important tasks in power system planning. In order to make the above decision reasonably, it is indispensable to develop effective assessment methods for power system dynamic reliability. If the simulation or analysis method proposed up to this time is singly used, the calculation time becomes too large or the calculation error become too large. Considering this situation, we developed a hybrid type assessment method which can drastically decrease the degree of the above problem. The basic conception of this method is as follows. (1) Three kind of tasks (simulation of power plant dynamics, construction of event trees, reliability analysis of protection systems) are carried out alternately using previous results. (2) First, event trees are constructed assuming that all protection systems act normally. These trees are gradually extended considering multi-failures of protection systems. This method was applied to a model power system composed of 5 generators, 11 lines and 19 nodes. Results of application confirm that this method can exactly assess power system dynamic reliability. This method has the merit that the trade-off between the decrease of calculation time and error can easily carried out by adjusting the extension degree of event trees and the details degree of power plant dynamics models. We are confident that an assessment expert system for power system dynamic reliability constructed due to this method in the future will greatly contribute to the improvement of the planning for preventing fault cascading of power systems