Part of #VARYING MODES OF VOLTAGE INSTABILITY# :
Publishing year : 1993
Conference : Eighth International Conference on Electricity
Number of pages : 12
Abstract: In reported incidents, different modes of voltage instability have occurred and each has presented in a different way. To identify energy engineers with different types, two incidents are described, which each started with a type of system voltage instability and culminated with radial voltage instability.
In one case, the events following the loss of a heavily loaded generator presented as "classic" system voltage instability. In this incident, operators were able to load, but not fast enough to prevent loss of other generators so that the situation reverted to radial voltage instability. In the second incident there was no initiating disturbance but very hot weather led to high levels of air conditioning load. This created a situation of & quot; slow & quot; system voltage instability where the system remained intact 12 minutes after the last shunt capacitors was switched on. A more serious collapse was avoided when radial voltage instability led to an exponentially increasing voltage reduction at three 500kV substations.
The fast switching voltages and currents triggered impedance protection on the 500kV lines, and they were interrupted by consumers at the three substations. In neither of these two incidents were the operators properly aware of the situation. The analysis of the incidents provided in this paper can provide important operational insights, showing the value of timely load shedding and the need to allow a margin of 25% from the radial voltage stability load limit