Voltage imbalance (also called voltage unbalance) is sometimes defined as the maximum deviation from the average of the three-phase voltages or currents, divided by the average of the three-phase voltages or currents, expressed in percent.
Imbalance is more rigorously defined in the standards6,8,11,12 using symmetrical components. The ratio of either the negative- or zerosequence component to the positive-sequence component can be used to specify the percent unbalance. The most recent standards11 specify that the negative-sequence method be used.
The primary source of voltage unbalances of less than 2 percent is single-phase loads on a three-phase circuit. Voltage unbalance can also be the result of blown fuses in one phase of a three-phase capacitor bank. Severe voltage unbalance (greater than 5 percent) can result from single-phasing conditions.
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Imbalance is more rigorously defined in the standards6,8,11,12 using symmetrical components. The ratio of either the negative- or zerosequence component to the positive-sequence component can be used to specify the percent unbalance. The most recent standards11 specify that the negative-sequence method be used.
The primary source of voltage unbalances of less than 2 percent is single-phase loads on a three-phase circuit. Voltage unbalance can also be the result of blown fuses in one phase of a three-phase capacitor bank. Severe voltage unbalance (greater than 5 percent) can result from single-phasing conditions.
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