science

Load shedding

Load shedding is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Load shedding rather than just read about it. In short: Load shedding (LS), often spelled loadshedding, is a protective method of emergency power control where, during a large disbalance between supply and demand, the demand (load) is intentionally disconnected ("shed") so that the available electricity supply within a safe timeframe can meet the remaining demand, thereby preventing a cascading collapse of the power grid. Load shedding is activated when the line frequenc…

Key takeaways

Load shedding belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Load shedding to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Load shedding from memory before moving on to harder problems.

Reference excerpt

Load shedding (LS), often spelled loadshedding, is a protective method of emergency power control where, during a large disbalance between supply and demand, the demand (load) is intentionally disconnected ("shed") so that the available electricity supply within a safe timeframe can meet the remaining demand, thereby preventing a cascading collapse of the power grid. Load shedding is activated when the line frequency becomes too low (under-frequency load shedding, UFLS) or the line voltage is below the specified level (under-voltage load shedding, UVLS). The very act of disconnecting the load introduces yet another disturbance into the grid, so the selection of the bus about to be shed is chosen based on the bus distance from the contingency location as well as economic considerations. The shedding can be shared via "rolling blackouts" or "rolling brownouts" (the typical situation, especially for UFLS: multiple areas of the grid shed the load in cooperative manner) or targeted via a "targeted blackout" (the load shedding is concentrated in a particular area). Typically the shedding is performed automatically in multiple stages, each with a pre-programmed threshold and the load amount to shed.

Under-frequency load shedding (UFLS) A UFLS scheme sheds predetermined amounts of load when the system frequency drops below specific thresholds. UFLS typically has short time delays, around 0.2 seconds. The UFLS schemes are most common and often represent a shared shedding paradigm.

Under-voltage load shedding (UVLS) A UVLS scheme is used to protect against excessive voltage decline by shedding load when voltage falls below specified thresholds. Time delays in UVLS are generally longer, typically above 3 seconds to prevent false tripping. Some research suggests using a slope-permissive UVLS design to shed load earlier based on predicted voltage drops. UVLS can be employed in targeted load shedding approaches. By the end of the 20th century, the main cause of blackouts in North America had switched from underfrequency to voltage collapse.

See also Demand response South African energy crisis

References

Sources Bevrani, Hassan; Watanabe, Masayuki; Mitani, Yasunori (2014-05-30). "Wide‐Area Measurement‐Based Emergency Control". Power System Monitoring and Control. Wiley. pp. 158–185. doi:10.1002/9781118852422.ch08. ISBN 978-1-118-45069-7. Retrieved 2025-05-18. Bevrani, Hassan; Hiyama, Takashi (2017-12-19). Intelligent Automatic Generation Control. CRC Press. ISBN 978-1-4398-4954-5. Retrieved 2025-05-18. Mozina, Charles J. (2007). 2007 60th Annual Conference for Protective Relay Engineers (PDF). doi:10.1109/CPRE.2007.359889. Retrieved 2025-05-18.

Worked examples

Example 1 — a first encounter with Load shedding

Start with the simplest possible case. Write down what Load shedding claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Load shedding before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Load shedding ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Load shedding

In research: Load shedding appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Load shedding in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Load shedding is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electric power distribution, Electricity stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Load shedding outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Load shedding in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Load shedding means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Load shedding out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Load shedding in simple terms?

Why does Load shedding matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Load shedding?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Load shedding.