VFD Reflected-Wave Cable Length Limit
The reflected-wave overvoltage on a long VFD-to-motor cable: L_crit = rise_time x cable_velocity / 2, and past it the peak terminal voltage doubles to 2 x the DC bus. Checked against the NEMA MG-1 Part 31 inverter-duty limit (3.1 x V_LL) and a general-purpose motor's ~1000 V. The limit is set by the drive rise time, not the horsepower.
Formula and source
cable_velocity = 0.01 x velocity_pct x 984; L_crit = rise_time x cable_velocity / 2; V_bus = sqrt(2) x V_LL; V_peak = 2 V_bus (run > L_crit); limits 3.1 x V_LL (inverter-duty) and ~1000 V (general-purpose).
VFD reflected-wave cable-length limit (NEMA MG-1 Part 31; transmission-line reflection), by name.
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