YORK YMC2 — WARNING - VSD - INPUT VOLTAGE IMBALANCE

The panel reads WARNING - VSD - INPUT VOLTAGE IMBALANCE — this exact wording, in this capitalisation, is the only form the manuals print. Both manuals place it among the warning messages, not among the shutdown messages, and both tie it to the input voltage of the VSD: the line-to-line voltages the control receives from the drive.

The supply line-to-line voltage imbalance is above 5%. On every VSD communications cycle the control takes the three line-to-line total RMS voltages Vab, Vbc and Vca received from the drive, averages them into Vavg, and calculates the imbalance as Vimb% = max(|Vab-Vavg|,|Vbc-Vavg|,|Vca-Vavg|) x 100%/Vavg — in words, how far the worst of the three line-to-line voltages sits from that average, expressed as a percentage of it; the max function simply selects the largest of its arguments. If Vimb% exceeds 5% continuously for 45 seconds, the warning is displayed.

• Line voltage imbalance above 5%, sustained continuously for 45 seconds. The imbalance is recalculated on every VSD communications cycle from the line-to-line RMS voltages (Vab, Vbc, Vca) that the drive reports; the manuals list no other cause for this warning.

• Warning threshold: line voltage imbalance above 5% of the average line-to-line voltage.
• Warning delay: 45 seconds of continuous exceedance, evaluated on every VSD communications cycle.
• Inputs used: the line-to-line total RMS voltages Vab, Vbc and Vca received from the drive.
• Clear condition: three consecutive imbalance readings below the 5% threshold.

No manual reset step is described for this warning — it clears by itself once the condition goes away. The manuals state: The 45 second timer shall reset and the warning shall clear if three consecutive imbalance readings fall below the 5% threshold. The supply imbalance therefore has to stay below 5% across three successive readings before the message leaves the display.