Influence of tie-line reactance on damping of inter-area oscillation mode

The influence of tie-line reactance on damping of inter-area oscillation mode is studied. The phenomenon of the inter-area mode damping ratio decreasing when inter-connection is strengthened is proposed. Main interconnected grids in China are tested by calculating sensitivity of eigenvalue to tie-line reactance, including Chuanyu-Mid China Grids, Northeast-North Grids, North-Mid Grids and Fujian-East Grids. A two- area system is constructed for further investigation. The study shows there is no strict linear relationship between tie-line reactance and damping of inter-area oscillation mode. For a large-scale system, the power transferred of which is comparatively small, it is possible that damping of inter-area mode decreases as tie-line reactance decreases, which is opposite to the commonly accepted opinion. Although the phenomenon is comparatively rare, it should be carefully paid attention to considering its strong influence under some critical stage. These tests also demonstrate that reinforcement of the conection between two bulk power grids is an effective way to mitigate oscillations in systems.