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Determination of weak transmission links by cluster analysis

Ertuğrul, Hamza Oğuz
Due to faults and switching, transmission lines encounter power oscillations referred as power swings. Although in most cases they do not lead to an eventual instability, severe changes in power flows on the lines may cause the operation of impedance relays incorrectly, leading to cascaded tripping of other lines. Out-of-Step tripping function is employed in modern distance relays to distinguish such an unstable swing but setting the parameters and deciding lines to be tripped require detailed dynamic power system modelling and analysis. The proposed method aims to determine possible out-of-step (OOS) locations on a power system without performing detailed dynamic simulations. Method presented here, is based on grouping of the buses by statistical clustering analysis of the network impedance matrix. Inter-cluster lines are shown to be more vulnerable to give rise to OOS as proven with dynamic simulations on IEEE 39 bus test system.