Expert System for Voltage Control in Restoration of EHV Power System after Complete Blackout

Abstract

This paper deals with voltage control in restoration of EHV power system. Restoration of power system is performed by energizing transmission lines in sequence from initial power sources. These operations have already been progammed into the expert system developed by the authors. However, energizing no-load transmission lines causes some bus voltages to rize 20% more than rated voltages. Transformers can tolerate 20% voltage rize only for 1 minute. Here, we supplement the expert system with a function of checking bus voltages and reactive powers of initial sources, and automatically switching reactors on. Conditions for switching reactors and selecting appropriate reactors, are written by rules, hence it is easy to modify them. Target of voltage control is to keep bus voltages within ±5%, and to keep reactive powers of generators within 30% of generator capacity. Applying this method to three basic restoration patterns of a model power system, shows that small adjustment of switching conditions is enough for two patterns, and some modification of restoration procedure is necessary for the other pattern to obtain good voltage profiles through the restoration process.