{"schemaVersion":1,"slug":"microgrid-underfrequency-shedding-interface","name":"Microgrid underfrequency shedding interface","kind":"symbol","abbreviation":"MUSI","aliases":["Microgrid load shedding and restoration","microgrids Microgrid load shedding and restoration","microgrids","Microgrids","Qualified underfrequency state","Assigned shedding outputs"],"category":"microgrid-systems","drawingTypes":["Schematic"],"referenceFamilies":["Manufacturer"],"summary":"Connects the selected frequency-based load reduction function to its assigned load groups.","description":["Connects the selected frequency-based load reduction function to its assigned load groups. Load management balances the available electrical supply against the loads that remain connected. Shedding, restoration, priority and proof of disconnection are separate control functions and should remain traceable to individual load groups.","In a microgrid island, the controller can disconnect lower-priority loads when a source is lost and later request restoration when the documented reserve and stability conditions permit it. For this reference, the drawing identifies “Qualified underfrequency state” at the input and “Assigned shedding outputs” at the output. Frequency thresholds require a protection study.","Identify each load group, priority, measured contribution and feedback. Shedding amounts, operating times and restoration conditions require the approved power-management design and the actual connected-load data. 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: Qualified underfrequency state. Identify its source device or document and the state represented on the drawing.","Follow the named output: Assigned shedding outputs. Cross-reference its destination and separate the command from confirmation that the equipment responded.","Frequency thresholds require a protection study.","Identify each load group, priority, measured contribution and feedback. Shedding amounts, operating times and restoration conditions require the approved power-management design and the actual connected-load data."],"drawingChecklist":["Label the source and connection reference for qualified underfrequency state.","Identify the destination and defined state of assigned shedding outputs.","Record the equipment or control-document revision supporting this functional block.","Check this application limit in the project design: Frequency thresholds require a protection study."],"distinction":"Frequency thresholds require a protection study. 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":"Microgrids"},{"label":"Input / boundary","value":"Qualified underfrequency state"},{"label":"Output / connection","value":"Assigned shedding outputs"},{"label":"Lookup label","value":"MUSI is a library lookup label, not a standard device designation."}],"references":[{"sourceId":"pi26-mg-study","relevance":"Public technical context for microgrid load shedding and restoration. Storage, protection, black start, load restoration and coordinated island operation. The application text and educational graphic are independently authored; the publisher does not certify this representation."}],"related":["microgrid-controller","generic-electrical-load","microgrid-rate-of-change-shedding-interface"],"artwork":"pi26-microgrid-underfrequency-shedding-interface","publishedOn":"2026-11-03","updatedOn":"2026-11-03","provenance":"independent-public-research","representation":{"type":"functional-block","focus":"microgrids","family":"microgrid-loads","input":"Qualified underfrequency state","output":"Assigned shedding outputs"},"plainEnglish":{"title":"What this block does","introduction":"Connects the selected frequency-based load reduction function to its assigned load groups.","example":"In a microgrid island, the controller can disconnect lower-priority loads when a source is lost and later request restoration when the documented reserve and stability conditions permit it. For this reference, the drawing identifies “Qualified underfrequency state” at the input and “Assigned shedding outputs” at the output. Frequency thresholds require a protection study.","drawings":"Start at the named input: Qualified underfrequency state. Identify its source device or document and the state represented on the drawing. Follow the named output: Assigned shedding outputs. Cross-reference its destination and separate the command from confirmation that the equipment responded.","terms":[{"name":"Input","meaning":"Qualified underfrequency state"},{"name":"Output","meaning":"Assigned shedding outputs"},{"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":["Qualified underfrequency state","MUSI","Assigned shedding outputs"],"caption":"A reading guide. The entry's original illustration and input/output facts describe this application.","sources":[{"label":"Avista Shared Energy Economy microgrid protection and control case study","url":"https://selinc.com/api/download/135486/"}],"profileId":"power-installation-microgrid-loads"},"url":"https://eloragrid.ai/symbols/microgrid-underfrequency-shedding-interface","illustration":{"url":"https://eloragrid.ai/tools/electrical-library/illustrations/microgrid-underfrequency-shedding-interface.svg","scope":"Original educational concept; not an official standard graphic or product footprint","license":"https://creativecommons.org/licenses/by/4.0/"},"sources":[{"id":"pi26-mg-study","publisher":"SEL","title":"Avista Shared Energy Economy microgrid protection and control case study","url":"https://selinc.com/api/download/135486/","scope":"Storage, protection, black start, load restoration and coordinated island operation.","type":"manufacturer","checkedOn":"2026-11-03","reuse":"link-only","relevance":"Public technical context for microgrid load shedding and restoration. Storage, protection, black start, load restoration and coordinated island operation. The application text and educational graphic are independently authored; the publisher does not certify this representation."}]}