Analysis of voltage collapse mechanisms in state space

The effects of the generator excitation current limit, the on-load tap changer (OLTC) and load dynamics on voltage stability are analysed in state space. The variation of the number and coordinates of the equilibrium points with parameters of the system are discussed. In addition, a small-disturbance voltage stability region of a simple system is constructed. When the dynamic aspect of voltage collapse is considered, it is more convenient to analyse it in the state space rather than in the input/output parameter space. The voltage stability of a system is determined by the dynamic characteristics of both the OLTC and the load. The generator excitation current limit affects the voltage stability by changing the small-disturbance voltage stability region and the equilibrium points of the system. After a small disturbance, the mode of voltage instability, fast instability or longer-term instability, depends on the composition of the load as well as the value of the system reactance.