  This paper shows that the variance of load bus voltage magnitude in a small
power system test case increases monotonically as the system approaches a Hopf
bifurcation. This property can potentially be used as a method for monitoring
oscillatory stability in power grid using high-resolution phasor measurements.
Increasing variance in data from a dynamical system is a common sign of a
phenomenon known as critical slowing down (CSD). CSD is slower recovery of
dynamical systems from perturbations as they approach critical transitions.
Earlier work has focused on studying CSD in systems approaching voltage
collapse; In this paper, we investigate its occurrence as a power system
approaches a Hopf bifurcation.
