An urgent direct load control scheme against voltage instability based on tendency analysis

In this paper, urgent direct load control is proposed as a remedy to voltage instability. It is an overall protection scheme. Tendency analysis combines the aspects of peak load forecasting, state estimation and operation pattern. The window nodes are selected by pattern recognition to observe the entire system from different angles to point out in advance those substations in which the loads are in excess of the rated loads. It is an effective method where groups of air conditioners are selected to act as voltage control equipments during a voltage crisis.