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Setor Elétrico
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Entry · Operation

ATLS: Compliance with System Limits

In what part of the time did the flows stay within the safety limits?

● checked against the primary source on Sep 30, 2026Source: ONS

Acronyms: ONS, National Electric System Operator.

In one sentence

Percentage of time in which flows selected by the ONS operated within the safety ranges recommended by electrical studies; the complement is the time above the limit.

Real example

Hours above the system limit over 12 months (ATLS)

10.2 hoursNature of the data: Calculated

Aug 2025 to Jul 2026 · FNESE flow (Northeast-Southeast/Center-West interconnection flow)

Source: ONS, Indicadores de confiabilidade da rede básica: ATLS (atendimento aos limites sistêmicos). Reference up to Jul 2026. Captured on Sep 30, 2026.

Hours above the limit over 12 months in a flow selected by the ONS, as the sum of the violation hours the ONS publishes: it is the time the ATLS deducts from the observed period.

See in the panel: Grid: restrictions

Calculated: Deterministic transformation made by Scrutiniums, with a published formula.

Why it matters

It is the public evidence of how long important grid flows spent outside the safety range, even without the limits being published.

How it is measured

ATLS = (1 − A/B) × 100%, with A the sum of the times of violation of the safety ranges and B the total observation period; violation intervals shorter than 10 minutes do not count, and there is a dead band of 50 MW or 5% of the range limit, whichever is greater. Monthly and annual aggregation.

Unit: percentage of observation time

Not to be confused with

  • Interchange between subsystems

    Interchange is the measured flow; the ATLS says in what part of the time selected flows stayed within the safety ranges. Neither dataset publishes the value of the limit.

What cannot be concluded

  • The indicator does not publish the value of the limit or the margin of each flow.
  • The ONS data file gives the value as a fraction from 0 to 1, although the dictionary says percentage.

Related entries

See in the panel

Official source

  • ONSGrid Procedures, Submodule 9.1, Basic Network reliability indicators (revision 2020.12, in force from Jan 1, 2021), item 2.7, accessed on Sep 30, 2026 

    Literal excerpt from the document
    Portuguese only“É o percentual de tempo em que os fluxos, definidos nos documentos normativos da operação e selecionados como relevantes para avaliação da segurança elétrica, operaram dentro das faixas de segurança recomendadas pelos estudos elétricos específicos.”
    Literal excerpt from the document
    Portuguese only“A = Somatório dos tempos de violação das faixas de segurança recomendadas pelos estudos elétricos específicos no período da agregação considerada. Não são considerados intervalos de tempo de violação com duração inferior a 10 (dez) minutos. B = Período total de observação da agregação considerada.”
    Literal excerpt from the document
    Portuguese only“É considerado, no cálculo do indicador, uma banda morta de 50 MW ou 5% do limite da faixa, o que for maior.”

Documents accessed and text checked on Sep 30, 2026.