{"schemaVersion":1,"slug":"station-clock-holdover-state-indication","name":"Station clock holdover-state indication","kind":"symbol","abbreviation":"SCHI","aliases":["Substation timing and event interfaces","substations Substation timing and event interfaces","substations","Substations","External reference loss","Clock holdover status"],"category":"measurement-protection","drawingTypes":["Schematic"],"referenceFamilies":["Manufacturer"],"summary":"Reports that the selected clock is operating without its normal external reference.","description":["Reports that the selected clock is operating without its normal external reference. A station time system provides a shared time reference for protection records, measurements and automation. Different devices can use different timing protocols, so the time source, distribution path and quality information must remain identifiable.","In a substation, a station clock can provide precision timing to process equipment and another timing interface to event recorders. The alarm system should distinguish loss of a distribution path from loss of the external time source. For this reference, the drawing identifies “External reference loss” at the input and “Clock holdover status” at the output. Holdover performance depends on the clock.","Show the source and client of each time connection. Required accuracy, holdover, protocol profile and loss-of-time behavior follow the selected application; a common timestamp format does not guarantee synchronized events. The functional block is an independent explanation of this named application. Equipment-specific ratings, terminal connections and operating conditions must be established in the project documentation."],"readingNotes":["Start at the named input: External reference loss. Identify its source device or document and the state represented on the drawing.","Follow the named output: Clock holdover status. Cross-reference its destination and separate the command from confirmation that the equipment responded.","Holdover performance depends on the clock.","Show the source and client of each time connection. Required accuracy, holdover, protocol profile and loss-of-time behavior follow the selected application; a common timestamp format does not guarantee synchronized events."],"drawingChecklist":["Label the source and connection reference for external reference loss.","Identify the destination and defined state of clock holdover status.","Record the equipment or control-document revision supporting this functional block.","Check this application limit in the project design: Holdover performance depends on the clock."],"distinction":"Holdover performance depends on the clock. This reference describes the named application; it does not establish a new IEC graphical symbol, an ANSI device-function number or an exact manufacturer connection diagram.","facts":[{"label":"Representation","value":"Functional block"},{"label":"Installation focus","value":"Substations"},{"label":"Input / boundary","value":"External reference loss"},{"label":"Output / connection","value":"Clock holdover status"},{"label":"Lookup label","value":"SCHI is a library lookup label, not a standard device designation."}],"references":[{"sourceId":"pi26-station-time","relevance":"Public technical context for substation timing and event interfaces. PTP, NTP, IRIG-B, pulse distribution, reference failover and timing quality. The application text and educational graphic are independently authored; the publisher does not certify this representation."}],"related":["sequence-of-events-recorder","phasor-measurement-unit","ptp-grandmaster-timing-interface"],"artwork":"pi26-station-clock-holdover-state-indication","publishedOn":"2026-11-03","updatedOn":"2026-11-03","provenance":"independent-public-research","representation":{"type":"functional-block","focus":"substations","family":"station-time","input":"External reference loss","output":"Clock holdover status"},"plainEnglish":{"title":"What this block does","introduction":"Reports that the selected clock is operating without its normal external reference.","example":"In a substation, a station clock can provide precision timing to process equipment and another timing interface to event recorders. The alarm system should distinguish loss of a distribution path from loss of the external time source. For this reference, the drawing identifies “External reference loss” at the input and “Clock holdover status” at the output. Holdover performance depends on the clock.","drawings":"Start at the named input: External reference loss. Identify its source device or document and the state represented on the drawing. Follow the named output: Clock holdover status. Cross-reference its destination and separate the command from confirmation that the equipment responded.","terms":[{"name":"Input","meaning":"External reference loss"},{"name":"Output","meaning":"Clock holdover status"},{"name":"Application reference","meaning":"An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections."}],"diagram":"flow","steps":["External reference loss","SCHI","Clock holdover status"],"caption":"A reading guide. The entry's original illustration and input/output facts describe this application.","sources":[{"label":"SEL-2488 satellite-synchronised network clock","url":"https://selinc.com/products/2488/"}],"profileId":"power-installation-station-time"},"url":"https://eloragrid.ai/symbols/station-clock-holdover-state-indication","illustration":{"url":"https://eloragrid.ai/tools/electrical-library/illustrations/station-clock-holdover-state-indication.svg","scope":"Original educational concept; not an official standard graphic or product footprint","license":"https://creativecommons.org/licenses/by/4.0/"},"sources":[{"id":"pi26-station-time","publisher":"SEL","title":"SEL-2488 satellite-synchronised network clock","url":"https://selinc.com/products/2488/","scope":"PTP, NTP, IRIG-B, pulse distribution, reference failover and timing quality.","type":"manufacturer","checkedOn":"2026-11-03","reuse":"link-only","relevance":"Public technical context for substation timing and event interfaces. PTP, NTP, IRIG-B, pulse distribution, reference failover and timing quality. The application text and educational graphic are independently authored; the publisher does not certify this representation."}]}