Microprocessor-Based Protective Relays

This article describes the benefits of microprocessor (P) relay performance and its capabilities beyond previous protective relaying technologies. This article also discusses a multiple quality-measurement approach to observing, measuring, and then calculating P relay reliability and unavailability. This is an important consideration for industrial and commercial facilities that are being required to repair or replace old electromechanical or solid-state (analog and digital) protective relaying equipment because of equipment malfunctions, misoperations, accidental tripping, or obsolescent parts. Although lP relays have been commercially available for more than 20 years and researched for the past 40 years, industrial and commercial plant engineers tend to be more reluctant to embrace the P technology. Electric power utilities in North America have aggressively selected to replace older protection equipment by upgrading and replacing the equipment with new P relays whenever and wherever possible. © 2009 IEEE.