How Current or Voltage Unbalance is calculated in Power Logic and ION meters?

Search FAQs

Issue
The formula that calculates the percent Current or Voltage Unbalance in Power Logic and ION meters has not been mentioned in Manuals.

Product Line
Power Logic and ION meters that are in compliance with IEC 61000-4-30

Environment
Power Monitoring Expert Vista Diagram, ION Setup, Technical Data sheet

Resolution
There are two commonly used definitions of Voltage Unbalance in the industry:

NEMA Definition: NEMA stands for National Equipment Manufacturers Association in USA.
True Definition: This definition of voltage unbalance is also known as ‘IEC Definition’ , ‘True definition’ or ‘Voltage Unbalance factor’.

According to IEC 61000-4-30 compliance and ION meters all PowerLogic™ and ION meters are compliant with the International Electrotechnical Commission's IEC 61000-4-30 (4-30) standard.

As per IEC 61000-4-30 the calculation of Unbalance is based on the following formula:
V_U = (V_N / V_P)*100%
where:
V_U= Percent Voltage Unbalance
V_N= Negative sequence voltage
V_P= Positive sequence voltage

As perNEMA MG1-14.34, Voltage and Current Unbalance percentage is calculated based on the following formula:
I_U= 100 * max ( |I₁- I_avg| , |I₂ - I_avg| , |I₃ - I_avg| ) / I_avg
where:
I_avg = (I₁ + I₂ + I₃) / 3
max ( |I₁ - I_avg| , |I₂ - I_avg| , |I₃ - I_avg| ) is the Maximum deviation from the mean value:
|I₁ - I_avg| = abs(I₁ - I_avg)
|I₂ - I_avg| = abs(I₂ - I_avg)
|I₃ - I_avg| = abs(I₃ - I_avg)

Voltage Unbalance is calculated the same as Current Unbalance formula based on NEMA method.

Example:
I_avg= (165.8 + 152.7 + 166.6) / 3 = 161.70
Maximum deviation from the mean value = max( abs(165.8 - 161.7) , abs(152.7 - 161.7) , abs(166.6 - 161.7) ) = max( abs(4.1) , abs(-9) , abs(4.9) ) = max( 4.1 , 9 , 4.9) = 9
I_U= (9 / 161.70) * 100 = 5.5658 ~ 5.6