Current Imbalance Definition
Current Imbalance Definition
(OP)
Please confirm:
Current Imbalance is defined as "(Imax-Imin)/Imax" ?
Shoud Iavg be the denominator instead of Imax?
Is the preferred term "Imbalance" or "Unbalance"?
Current Imbalance is defined as "(Imax-Imin)/Imax" ?
Shoud Iavg be the denominator instead of Imax?
Is the preferred term "Imbalance" or "Unbalance"?






RE: Current Imbalance Definition
This is the basis for the NEMA limitations on "voltage unbalance" in MG-1.
RE: Current Imbalance Definition
Another way to define unbalance (from the IEC world) is to define it as the ratio of negative phase sequence voltage to positive phase sequence voltage. Makes better engineering sense to me, but the American way is aesier for "back of the envelope" calcs using magnitudes only. So you pays your money and takes your choice!
Bung
Life is non-linear...
RE: Current Imbalance Definition
Note the difference between using max and average is small.
There is a big difference between "max - min" and "max deviation from average" Typically almost a factor of 2 difference.
With unbalance as defined by dpc (max deviation from average over average), unbalance is typically a close approximation to negative sequence as fraction of positive sequence. Unbalance can be calculated with magnitudes only. Negative sequence requires phase information as well.
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RE: Current Imbalance Definition
IEEE Recommended Practice for Monitoring Power Quality Std 1159-1995 lists "Voltage Imbalance(or unbalance)" in Part 4.4.4 as equal to 100 x (max deviation from average voltage)/average voltage. It does not list parameters for current imbalance.
I have seen the terms 'imbalance', 'inbalance', and 'unbalance' used interchangeably.
RE: Current Imbalance Definition
RE: Current Imbalance Definition
RE: Current Imbalance Definition
a- Difference in magnitude of rms phase current that exceed a given percentage.
b- Measuring the magnitude of negative sequence current, but calibrated in term of I^2t characteristics of the machine.
Relay manufacturer suggest the following calculation methods for unbalance current:
UB% = |Imax-Iav|/Imax.100
See site below:
http://www.automatictiming.com/pdf_div/3phase_current_unbalance.pdf
Other manufacturers suggest the following calculation method with somehow different than above.
Case a: Iav > Iflc; ==> UB% =|Imax-Iav|/Iav.100
Case b: Iav < Iflc; ==> UB% = |Imax-Iav|/Iflc .100
See page 1-4 for Calculation Method:
http://www.geindustrial.com/products/manuals/mm3/mm3-a4_1.pdf
Where:
UB% = Unbalance phase current in %
Iav = average phase current
Imax = current in a phase with maximum deviation from IAV
Iflc = motor full load current setting
RE: Current Imbalance Definition
Thanks cuky for your input. Red star for you too.
RE: Current Imbalance Definition
RE: Current Imbalance Definition
Iavg = (Imax + Imin)/2
%Ia = ((Ia - Iavg) / Iavg) * 100
%Ib = ((Ib - Iavg) / Iavg) * 100
%Ic = ((Ic - Iavg) / Iavg) * 100