Measurement-Based Voltage Stability Assessment Considering Generator VAR Limits

This paper proposes a measurement-based voltage stability assessment method considering VAR limits of generators. Traditional measurement-based methods for monitoring a load bus or a load area often simplify the external system as a simple constant electromotive force (e.m.f.) behind a Thevenin impedance, which may give inaccurate voltage stability margin when some external generator reaches its VAR limit. In this paper, a novel method is proposed to consider the VAR limits of generators by deriving a relationship between the variations of their e.m.f. and the load, which can be identified and tracked in real time. Thus, a more accurate voltage stability margin is derived by an analytical expression under variations of both generator terminal voltages and loads. The proposed method is compared with a typical Thevenin method and demonstrated on a two-area system and the IEEE 39-bus power system.