We suggest a new mechanism for interarea electric power system oscillations
in which two oscillatory modes interact near a strong resonance to cause o
ne of the modes to subsequently become unstable, The possibility of this me
chanism for oscillations is shown by theory and computational examples. The
ory suggests that passing near strong resonance can be expected in general
power system models. The mechanism for oscillations is illustrated in 3- an
d 9-bus examples with detailed generator models.