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01 · Power systems · protection logic

Smart-Grid UFLS Relay — ONEE & SENELEC

UFLS relay model for two grid contexts, with a six-state Stateflow automaton for staged shedding, restoration and validation.

IEC 61850
Smart-Grid UFLS Relay — ONEE & SENELEC
PROJECT CONCEPT VIEW

The illustration follows a frequency event from detection to selective load shedding: as system frequency crosses predefined thresholds, non-critical feeders are disconnected in stages while essential demand is preserved, giving generation and load time to rebalance.

Problem

Frequency events require protection logic that reacts quickly without hiding the assumptions behind each threshold.

Solution

A staged UFLS controller with explicit states, thresholds and restoration rules.

Build path

  1. Define grid assumptions and frequency thresholds.
  2. Build the Stateflow state machine.
  3. Run disturbance scenarios.
  4. Check staged shedding and restoration behaviour.

Discussion

The value of the model is traceability: when the relay acts, why it acts, and how the grid returns toward normal operation remain visible.