Motor Derating for Voltage Unbalance (NEMA MG-1)
Turns a measured three-phase voltage unbalance into a NEMA MG-1 motor derating factor and the do-not-operate flag above 5%: unbalance = max deviation from the average / the average (460/455/450 V -> 1.1% -> derate ~0.98). The MG-1 curve is interpolated; above 5% the motor should not be operated. Correct the unbalance source first; the manufacturer and MG-1 govern the final figure.
Formula and source
v_avg = (Vab + Vbc + Vca)/3; unbalance% = max deviation from v_avg / v_avg x 100; derate_factor read off the NEMA MG-1 curve (1% -> ~0.98, 5% -> ~0.75), interpolated; over 5% -> do not operate.
Motor derating for voltage unbalance, NEMA MG-1; the unbalance per the NEMA definition (max deviation from the average over the average), by name.
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