Event caption PQ-221: the waveform that was not ‘just a blink’

Event: PQ-221
Source: Plant PQ monitor · Feeder West
Format: Caption sheet for one waveform. Not a harmonics textbook.

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Caption block

Event ID: PQ-221
Type: voltage sag
Retained voltage: ~72% Vnom
Duration: 180 ms
Phase: A-B heavy
Time: 14:03:11 local
Upstream: utility reclose suspected

If duration is blank, every department invents a different story.

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Who felt it

| Island / load | Effect | Expected by ride-through class? | | --- | --- | --- | | Packaging VFDs | Trip | No — class underspec’d | | UPS process island 2 | Held | Yes | | PLC cabinet (off-island) | Brown reboot | Predictable failure | | Abatement | Trip → tool abort | Not on UPS list |

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Wrong narratives heard same day

1. “Blink — ignore.” (180 ms is not ignore for VFDs.)
2. “Buy bigger UPS for everything.” (No shed / class review.)
3. “Utility fault — not our problem.” (Ride-through class is yours.)

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Caption → actions

1. File PQ-221 with waveform + load effects in one packet.
2. Reclass packaging VFDs ride-through or move controls on-island.
3. Put abatement on the critical dependent list (see UPS island logic).
4. Stop closing tickets as “blink” without duration.

Event IDs beat hallway mythology.

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Adjacent fences

Black-start scripts own grid-loss decision drills. UPS cascade essays own dip failure trees. Invoice autopsies own tariff lines. PQ-221 owns one sag as evidence. Do not fund a second generator to skip a caption sheet.

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Close

A waveform without a caption is art. A caption without actions is filing. PQ-221 needs both—or the next sag reprints the scrap.