Types of Protective Relays: Protective relays are categorized by their mechanism (electromagnetic, static, mechanical) and function (time-based, current, voltage). According to the Institute of Electrical and Electronic Engineers (IEEE C37. 100-1992), a protective relay is: “A relay whose function is to detect defective lines or apparatus or other power system conditions of an abnormal or dangerous nature and to initiate appropriate control circuit action. For example, unselective protection operation during a medium voltage network fault will cause an outage for an unnecessarily large number of consumers. The selection and applications of. Relay characteristics are very useful in determining the relay setting, which in turn will determine relay speed, sensitivity, and selectivity for protection from power system short-circuits.
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