Different technology has been used in the past to implement protection functions that properly detect disturbances in the power systems and initiate the disconnection of the faulted components. Despite the developments of complex algorithms for implementing protection functions, the microprocessor-based relays were marketed in the 1980s. Those relays performed basic functions, took advantage of the hybrid analog and digital techniques, and offered good economical solutions. The performance of these relays, however, was only adequate but their introduction did a lot of good to the highly conservative worked of power system protection. Continuous advances in electronics, combined with extensive research conducted in microprocessor-based systems, led to a few applications in which multiple functions were performed by a microprocessor relay.
The following PDF is the report of the relaying practices subcommittee.
Download Understanding microprocessor-based technology applied to relaying
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