Three-phase Voltage Unbalance Calculator
This calculator uses the formula as defined by NEMA to determine Voltage Unbalance. Voltage Unbalance = 100 x Maximum Deviation from Average Voltage / Average Voltage.

Did you know that experts in the field of electrical energy estimate that more than half of the worlds electricity may be consumed by three-phase AC Induction Motors? That's right, more than half! Because of that, Voltage Unbalance in three-phase motors is an important subject. Here's why!

When there are unequal incoming voltages between the three legs of a motor, the motor runs hotter. The reason why an unbalanced motor runs hotter is because as the voltage is out of balance so is the motor winding currents. A small voltage unbalance causes a larger current unbalance, which in turn causes the motor to run hotter because the unbalanced magnetic fields created by the windings are working against each other. This rise in temperature causes two main problems.

Problem 1.  Unbalanced voltage reduces motor life by shortening the lifespan of it's insulation. Using this calculator's formula, a voltage imbalance of greater than 1% causes the motor to run hotter. The temperature of the windings (in degrees Celsius) will increase by twice the percent of voltage unbalance squared. Every 10 degrees Celsius cuts the insulation life in half, a 3% voltage unbalance reduces the life of the windings to almost one-fourth it's expected lifespan. 2x(3x3)=18 degrees Celsius

Problem 2.  Unbalanced voltage wastes energy by reducing the efficiency of the motor. An unbalanced AC Induction Motor's Rotor will not run at full rated RPM, this is because the rise in temperature creates what is called "slip". An example of this would be an unbalanced motor running a pump, that combination will take longer to pump the same amount of volume over time than a pump powered by a balanced motor. The end result, energy is wasted!

One leaking faucet dripping at a rate of 30 drops a minute wastes 1,388 gallons of water a year, how much electricity would you estimate is wasted in one year in just the U.S. due to the voltage unbalance of all those motors? The U.S. Department of Energy published an article on June 29, 2007 estimating that it may be as much as \$28 Billion a year!
1. Measure the voltage across each of the three phases from L1 to L2, L1 to L3, and L2 to L3.
2. Enter the voltages in the below designated textboxes.
3. Click the Calculate button to get the results.

 L1 to L2   L1 to L3   L2 to L3 Unbalance =

send the formula for calculate the unbalance voltage in %
shankar 03/19/2010
pel.diagonalley@gmail.com
skilef 05/20/2010
The formula as defined by NEMA is... Voltage Unbalance = 100 x Maximum Deviation from Average Voltage / Average Voltage. Articles Example: 100 X 5 / 222 = 2.25
Thanks
Gene 06/24/2010
Dear Sir,

I want to know the formula of unbalance current as well as unbalance power & what is the effect on electrical equipments due to above cause?
AHFAZ 02/06/2011
AHFAZ, Below the Comment box there are two links to two more articles on Unbalanced Voltage with solutions for the problem. You may find those helpful.
You may want to check out the Phaseback unit from Applied Energy. www.phaseback.com. They use a ferro magnetic resonate circuit (if I am calling it correctly) that balances voltages to within a few degrees of each other. They also have a DVS - drive voltage stabalizer that goes on the output of a drive for significantly reducing the amount of harmonics into the motor extending its life.
Preston Cobb 03/25/2013
Can I have the full steps to calculate unbalance voltage.
Is there a automatic calculator where you put in the values and get the result
atendra sen 10/25/2013
I''m not aware of that atendra other than what is on this page!

That''s pretty cool Preston!
good afternoon
I''m doing a refrigeration program and have had trouble making this voltage unbalance formula in excel, I could send this formula to my email
thank you very much

Henry Gonzalez
Henry Gonzalez 11/10/2013
Henry, try the below two links. They will get more into depth on the subject.