Analysis of tap-changer dynamics and construction of voltage stability regions

The destabilizing behavior of onload tap changers (OLTC) is an important mechanism responsible for the voltage collapse of interconnected power systems. A nonlinear dynamic model of the OLTC, impedance loads and decoupled reactive power-voltage relations is used to reconstruct the voltage-collapse phenomenon. Trajectories leading to a monotonic fall of bus voltages are obtained from initial conditions outside the stability region of a simple power network. The construction of voltage stability regions is desirable for the prevention of voltage collapse. Based on the proposed M-bus power network model, this research results in (1) a simple criterion for stability of an equilibrium, and (2) a method to obtain a stability region by forming the union of hyperbox subsets of the true region. The theoretical foundations of the proposed method, i.e., characteristics of the equilibria and monotonic behaviour of system trajectories, are thoroughly studied.>