摘要：Loop flows in the European power system (ENTSO-E CE) not only limit trade capacity,but also compromise power system operational security.In order to reduce unscheduled power transfers, phase shifters are most commonly used,usually installed on tie-lines.Where these devices are not available or their control range has been exhausted,and the unscheduled power transfer is greater than the allowable,transmission grid operators,in extreme cases,to maintain the integrity of their own systems may decide to introduce topological changes resulting in interconnection weakening.Such action reduces the undesired power transfer,but at the same time it affects the frequency and the damping of inter-area oscillations in the ENTSO-E CE system.The results presented in this paper provide a qualitative assessment (show trends of changes) of the impact of the Polish NPS (National Power System) border lines’ outages on the damping and frequency, and the contribution of NPS generators to inter-area oscillations.Due to the problems with low frequency oscillation damping in ENTSO-E CE,any reduction in the damping or frequency from the initial state should be considered a potential threat to secure system operation.
关键词：system security;loop flows;inter-area oscillations;small signal stability
