Application of the fault tree analysis for assessment of power system reliability

Assessment of Power System Reliability

A method for analysing the reliability of a transmission grid

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A method for the probabilistic security analysis of transmission grids

This paper investigates the method to overcome the problems that simulation methods require too much calculation cost in order to assess accurately transient phenomena cased by faults of power systems. At first, transient stability which is the most important characteristic to assess in power systems is adopted as the object one and critical fault clearing time functions are newly defined by taking notice of the fact that transient stability is mainly controlled by fault clearing time and load. Next, the method to be able to assess accurately and efficiently transient stability has been developed. Finally, it has been applied to the transient stability assessment of a three-phase-to-ground fault in the model power system with 5 generators. Results of application have been clarified the effectiveness of the developed method.

Power system transient stability assessment using critical fault clearing time functions

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.

T. Miki

Papers

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