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- Q503732 abstract "A relay is a device which is operated by a variation in its electrical or physical conditions to effect the operation of other devices in an electric circuit. A protective relay is a relay, the principal function of which is to protect service from interruption or to prevent or limit damage to apparatus. In electrical engineering, a protective relay is a device designed to trip a circuit breaker when a fault is detected. The first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as over-current, over-voltage, reverse power flow, over- and under- frequency. Microprocessor-based digital protection relays now emulate the original devices, as well as providing types of protection and supervision impractical with electromechanical relays. Electromechanical relays provide only rudimentary indications of involved phase and zone targets. In many cases a single microprocessor relay provides functions that would take two or more electromechanical devices. By combining several functions in one case, numerical relays also save capital cost and maintenance cost over electromechanical relays. However, due to their very long life span, tens of thousands of these "silent sentinels" are still protecting transmission lines and electrical apparatus all over the world. An important transmission line or generator unit will have cubicles dedicated to protection, with many individual electromechanical devices, or one or two microprocessor relays.The theory and application of these protective devices is an important part of the education of an electrical engineer who specializes in power systems. The need to act quickly to protect circuits and equipment as well as the general public often requires protective relays to respond and trip a breaker within a few thousandths of a second. In some instances these clearance times are prescribed in legislation or operating rules. A maintenance or testing program is used to determine the performance and availability of protection systems.Based on the end application and respective user geography, there are various standards such as ANSI C37.90, IEC255-4, IEC60255-3, IAC, etc. that govern the response time of the relay to the fault conditions that may occur.".
- Q503732 thumbnail Protective_Relays_Hydroelectric_Station.JPG?width=300.
- Q503732 wikiPageWikiLink Q118801.
- Q503732 wikiPageWikiLink Q174053.
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- Q503732 wikiPageWikiLink Q43035.
- Q503732 wikiPageWikiLink Q4653041.
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- Q503732 wikiPageWikiLink Q550262.
- Q503732 wikiPageWikiLink Q663542.
- Q503732 wikiPageWikiLink Q856535.
- Q503732 wikiPageWikiLink Q988780.
- Q503732 type Thing.
- Q503732 comment "A relay is a device which is operated by a variation in its electrical or physical conditions to effect the operation of other devices in an electric circuit. A protective relay is a relay, the principal function of which is to protect service from interruption or to prevent or limit damage to apparatus. In electrical engineering, a protective relay is a device designed to trip a circuit breaker when a fault is detected.".
- Q503732 label "Protective relay".
- Q503732 seeAlso Q1756067.
- Q503732 depiction Protective_Relays_Hydroelectric_Station.JPG.