The problem of early on-line detection of inter-area
electro-mechanical oscillations in power systems is considered. The
main objective is to give the transmission operator qualitative
information regarding stability
margins. The observed signal consisting of currents, voltages and
angle differences is modeled using non-stationary second order
autoregressive model. Bayesian estimation of the system is based on
the forgetting approach. The stability margins are obtained as
posterior probabilities that the poles of the estimated system are
unstable. The approach
is demonstrated on real retrospective data recorded in a 500 kV
power grid and voltage data obtained by numerical simulations.