TABLE OF CONTENTS The reliable operation of large power systems with small stability margins is highly dependent on control systems and protection devices. Progress in the field of microprocessor systems and demanding requirements in respect of the performance of protective relays are the reasons for digital device applications to power system protection. The superiority of numeric protection over its analogue alternatives is attributed to such factors as accurate extraction of the fundamental voltage and current components through filtering, functional benefits resulting from multi-processor design and extensive self-monitoring, etc. However, all these reasons have not led to a major impact on speed, sensitivity and selectivity of primary protective relays, and the gains are only marginal; this is so because conventional digital relays still rely on deterministic signal models and a heuristic approach for decision making, so that only a fraction of the information contained within voltage and current signals as well as knowledge about the plant to be protected is used.
The performance of digital relays may be substantially improved if the decision making is based on elements of artificial intelligence (AI). Relays capable of that ought to have the following properties:
tripping decisions ought to be based on several criteria with adaptable weighting factors
uncertainty with regard to the signals and settings ought to be modelled qualitatively
the consequence of a wrong decision ought to be considered, making the relays more inclined to trip or more inclined not to trip,...
