Dynamic index assessment for voltage stability in electric power systems

Voltage instability as a nonlinear dynamic phenomenon is investigated, by introducing a dynamic load flow (LF) Jacobian matrix as a specific index to assess the nonexistence of a stable new equilibrium point in response to perturbations. Reference is made to the Lyapunov exponent and bifurcation theories to provide extension of steady-state based indices for voltage stability, this time taking care of system differential equations, to a continuous monitoring of system distance from collapse during transients caused by step perturbations. Theoretical results are validated on the IEEE 30-node test network, accounting for the effect of typically committed components and regulation loops, such as synchronous generators, and voltage dependent loads under load tap changing transformers. Comparison with traditional modal analysis is also provided for sake of completeness.