Analysis of voltage collapse mechanisms in state space

The effects of the generator excitation current limit, the on-load tap chan ger (OLTC) and load dynamics on voltage stability are analysed in state spa ce. The variation of the number and coordinates of the equilibrium points w ith parameters of the system are discussed. In addition, a small-disturbanc e voltage stability region of a simple system is constructed. When the dyna mic aspect of voltage collapse is considered, it is more convenient to anal yse it in the state space rather than in the input/output parameter space. The voltage stability of a system is determined by the dynamic characterist ics of both the OLTC and the load. The generator excitation current limit a ffects the voltage stability by changing the small-disturbance voltage stab ility region and the equilibrium points of the system. After a small distur bance, the mode of voltage instability, fast instability or longer-term ins tability, depends on the composition of the load as well as the value of th e system reactance.