Resonance of Forcing Oscillations and Inter-Area Modes in the Nordic Power System

Fingrid has had a real-time oscillation detection system in use for a couple of years. It has been noted that most of the observed oscillation incidents have been caused by forced oscillations. These incidents have not been critical to the power system operation so far but in the worst case they could risk the system security. Therefore, in this paper, the most significant forced oscillation events in the Finnish power system have been studied from the recent years. The results show how the observed forced oscillations are dependent on many factors but the most important are location of the forced oscillation source, damping of the inter-area oscillation mode, and frequencies of the forced oscillation source and the interarea oscillation mode in the system. It is concluded that the observations follow relatively well the general theory of resonance summarized in the paper.