Evaluation of reactive power reserves with respect to contingencies

Following a disturbance, most generators, synchronous condensers and static var compensators of a power system react to maintain their voltages at (almost) constant values, by producing more reactive power. This is possible as long as no physical limit prevents this additional reactive power from being produced. When such limits are encountered, transmission voltages fall down more or less progressively, until instability occurs either in the form of a loss of synchronism (insufficient voltage support to transfer active power over long distances) or a voltage instability at the load ends (inability of the transmission and generation system to meet the load demand) [1, 2].