Abstract :
Due to the abrupt nature of the major disturbances that may endanger the security of an electrical network, it is but natural to conclude that some of the corrective actions should also be rapidly applied automatically for early completion, in a bulk, non-linear fashion; the linear controls can then take over and use up the design margin of the system to optimize its subsequent security. These techniques are often almost equivalent to reducing the absolute contingency level of the disturbance by one, that is from the complete network, by using reliable and well coordinated automatic schemes, in place of some overdesign to be sacrificed at the first event. Amongst the many non-linear automatic operations available to the designer1, one finds generator dropping, load shedding, reactive elements switching, line switching, etc. This paper outlines the main aspects of three such schemes designed to meet some of Hydro-Quebec´s particular system problems in order to improve its stability and security; these are: Automatic removal of 735 kV line compensation inductors for stabilization purposes, automatic generator dropping system for the Churchill Falls generation and transmission network and, automatic load shedding system for the interconnected network.
