Voltage Imbalance Calculation Method with AVG/MIN/MAX Data

[Billgas]

Good Morning
I have a question on how to calculate voltage imbalance.

The data that have contains AVERAGE MINIMUM and MAXIMUM values for each of three phases, with records recorded one time per second.

I know the voltage imbalance percentage formula, and repeat it here:

Formula stating Voltage unbalance=100 x Max. deviation from average voltage/Average voltage

For example, if measured line voltages were 455, 460, and 492, the average would be 469 volts (455 + 460 + 492 = 1407 / 3 = 469). The maximum deviation from that average is 23 volts (492 - 469 = 23). To find the voltage unbalance, solve the equation for the average voltage and the maximum
voltage deviation: Formula stating Voltage unbalance=100 x (23/469) = 4.9%

My question is which voltage values should be used in the calculation.

I think that I should use the AVERAGE of all (AVGab +AVGbc + AVGca)/3, and the maximum deviation being the largest of the AVERAGE from each phase AVG. correct?

 

[Billgas]

I should have mentioned that the average value recorded is not a simple average of the MIN and MAX values, it must be calculated during the one second before recording the value.

 

[dpc]

The basic intent would be to use steady-state voltage levels. The "Minimum" and "Maximum" voltages could contain temporary voltage dips or swells that would not really be relevant to voltage balance.

Assuming the "Average" values represent the average rms voltage over the one second interval, that's what I would use, but even that might be misleading.

Voltage imbalance is a long-term problem, especially for motors. Short periods (a few seconds) of voltage imbalance are not generally a major concern as long the the voltage transient is not too severe and doesn't occur too frequently.