Functional block · MUSI

Microgrid underfrequency shedding interface

Functional block · Microgrids

An independently authored application reference. The drawing shows the named function or circuit relationship; use the project legend and selected equipment documentation for its drafting form and connections.

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In plain English

What this block does

Connects the selected frequency-based load reduction function to its assigned load groups.

A simple 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.

A reading guide. The entry's original illustration and input/output facts describe this application.

What the drawings help you do

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.

Input: Qualified underfrequency state
Output: Assigned shedding outputs
Application reference: An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.

Read the source: Avista Shared Energy Economy microgrid protection and control case study

Microgrid underfrequency shedding interface: original educational illustration — Original educational illustrationSee source and graphic notes

What it represents

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.

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.

How to read it

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.

Information to show or reference

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.

A distinction that matters

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.

Sources you can follow

These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.

Avista Shared Energy Economy microgrid protection and control case study

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.

SEL · Public reference checked 3 November 2026 · Link only

About this graphic

This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.

SVG and DXF downloads contain this original artwork. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.

Entry JSON · Entry Markdown · Last editorial update: 3 November 2026

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