Different types of voltage instability

In reported incidents, different types of voltage instability have occurred and each has presented in a quite distinct manner. To better acquaint power engineers with the different types, two incidents are described as each commenced with a type of system voltage instability and culminated with radial voltage instability. In neither of these two incidents were operators fully aware of the situation. The analysis of the incidents provided in this paper can give important operational insights. In particular it shows the value of timely load shedding and the need to allow a 20% margin from the radial voltage stability limit.>