RT-SVX36G-EN 107
Unit Start Up
Voltage Imbalance
Excessive three phase voltage imbalance between phases will cause motors to overheat and
eventually fail. The maximum allowable voltage imbalance is 2%. Measure and record the voltage
between phases 1, 2, and 3 and calculate the amount of imbalance as follows:
V1, V2, V3 = Line Voltage Readings
VD = Line Voltage reading that deviates the farthest from the average voltage.
Example: If the voltage readings of the supply power measured 221, 230, and 227, the average volts
would be:
VD (reading farthest from average) = 221
The percentage of Imbalance equals:
The 2.2% imbalance in this example exceeds the maximum allowable imbalance of 2.0%. This
much imbalance between phases can equal as much as a 20% current imbalance with a resulting
increase in motor winding temperatures that will decrease motor life. If the voltage imbalance is
over 2%, notify the proper agencies to correct the voltage problem before operating this
equipment.
% Voltage Imbalance =
100 X AV - VD where;
AV
A V (A ver age V o ltag e ) =
Volt 1 + Volt 2 + Volt 3
3
221 + 230 + 227
= 226 Avg.
3
100 X 226 - 221
= 2.2%
226
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