Monitor

The power-grid modal-growth detector — the first domain-specific early-warning detector in the programme to beat the generic suite on a real corpus, and the operational core that a live monitor scores on each window.

What it is for

When a disturbance leaves an electromechanical mode under-damped, the amplitude of the cross-bus voltage deviation grows exponentially: the real part σ of the dominant mode's eigenvalue turns positive (negative damping), the canonical wide-area-monitoring early-warning quantity. This module estimates that growth rate directly and passively — it reads bus voltages and returns a growth rate; it never actuates and never recalibrates, so its operating point is fixed by the offline certification (bench.grid_modal_head_to_head).

Contract

• cross_bus_deviation — the per-sample mean absolute deviation of the bus voltages from their cross-bus mean, an amplitude envelope of the collective mode.
• per_bus_deviation — the same deviation kept per bus, so a growth rate can be measured on each bus and the most unstable one taken.
• envelope_growth_rate — the exponential growth rate σ of a deviation envelope (the slope of its log against time); σ > 0 is a growing, unstable mode, σ < 0 a damped one. A recency_top weighting lets later samples count for more, because a real instability accelerates toward onset.
• modal_growth_score — one segment's σ under the "focal" (most unstable bus) or "mean" (whole network) aggregation; the certified default is "focal" with a recency weighting.

All voltage matrices and deviation envelopes are non-empty, finite, real, and non-coercive; text, boolean, complex, negative-amplitude, and broken-protocol evidence is rejected before centring or logarithms. Sampling rate, recency weighting, and fit-quality gates require finite non-boolean real scalars whose derived time/weight geometry is also representable. Undefined telemetry never collapses to a benign zero growth score.

On the PSML 23-bus corpus, labelling transitions by disturbance type (a label independent of the growth statistic, so the comparison is not circular), the detector leads 36 of 90 growing-instability transitions at a matched ten-percent false alarm where every generic member is at chance.

References

• Zheng et al. 2021 — the PSML power-system dataset (23-bus millisecond-level PMU measurements) with disturbance-type annotations.
• Kundur 1994, Power System Stability and Control — small-signal (modal) stability: a mode's eigenvalue real part is its growth rate, the sign of instability.

::: scpn_phase_orchestrator.monitor.grid_modal_growth