Generator reactive power limits and voltage stability

Generator reactive power limit is a key factor in voltage instability. When the field or armature current limit becomes active, the generator reactive power limit becomes voltage dependent. These operational limits and the shifting between field limit and armature limit, are fully investigated. Further, careful examination of generator reactive power characteristics, reveals the effect of generator reactive power capability on system voltage stability. It is shown that a generator can be active or passive in supporting voltage stability, even when its reactive power is limited. An indicator is proposed for identifying critical generators, based on this observation