PLANNING AGAINST VOLTAGE COLLAPSE.

Several systems have experienced voltage collapse, and the Task Force's questionnaire indicates a need for a widely accepted procedure for dealing with the voltage collapse problem in system planning. The object of this report is to present a procedure and to establish guidelines for the use of system planners in order to prevent voltage collapse. The report contains an explanation of the voltage collapse problem, and how it is influenced by transmission system characteristics, the steady-state and the dynamic behaviour of the load, as well as the overall system control. Experiences from actual system disturbances are examined together with conclusions from the questionnaire. Prefault conditions are discussed, and it is suggested that the use of n - 2 security in reactive planning could be justified in order to obtain a probability of failure due to voltage collapse consistent with normal practice regarding transient stability. A planning procedure based on a normal load-flow program is established, and practical guide lines for planners are drawn up. This procedure is much faster than procedures based on dynamic calculations. Finally an example to illustrate the method is given.