Enter the maximum deviation from the average (volts) and the average voltage (volts) into the Calculator. The calculator will evaluate the Voltage Unbalance. 

Voltage Unbalance Formula

VU = MD / Vave *100


  • VU is the Voltage Unbalance (%)
  • MD is the maximum deviation from the average (volts)
  • Vave is the average voltage (volts)

To calculate Voltage Unbalance, divide the maximum deviation from the average voltage by the average voltage, then multiply by 100.

How to Calculate Voltage Unbalance?

The following steps outline how to calculate the Voltage Unbalance.

  1. First, determine the maximum deviation from the average (volts). 
  2. Next, determine the average voltage (volts). 
  3. Next, gather the formula from above = VU = MD / Vave *100.
  4. Finally, calculate the Voltage Unbalance.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

maximum deviation from average (volts) = 15

average voltage (volts) = 90


What is Voltage Unbalance?

Voltage unbalance refers to the condition where the voltage magnitudes or the phase angle difference among the three phases of a three-phase system are not equal. This can lead to inefficient operation and potential damage to electrical equipment.

Why is it important to calculate Voltage Unbalance?

Calculating Voltage Unbalance is crucial for maintaining the efficiency and longevity of electrical systems. It helps in identifying issues that may cause excessive heating in motors and transformers, leading to premature failure or inefficient energy use.

How can Voltage Unbalance affect electrical equipment?

Voltage Unbalance can cause motors to overheat, reduce their lifespan, increase energy consumption, and lead to uneven load distribution. It can also cause nuisance tripping of circuit breakers and reduce the overall efficiency of electrical systems.

What are some common causes of Voltage Unbalance?

Common causes include unbalanced loads, uneven distribution of single-phase loads across a three-phase system, faulty equipment, and variations in the supply voltage. Identifying and correcting these causes can help mitigate the effects of Voltage Unbalance.