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I'm a Brazilian (so not a native English speaker) who just came across the user guide of a power quality analyser which has, among its features, measurement of both "voltage unbalance" as well as "voltage imbalance". The problem is that I'm not sure what is being talked about here... For instance, Google Translator sometimes gives me the same meaning for both words - in Portuguese, "desequilíbrio" - but sometimes I got "desequilíbrio" for Unbalance and "desbalanço" for Imbalance, so this could actually mean two different things. Unfortunately I went to Google and found some resources saying that Unbalance and Imbalance are synonyms in the context of Electrical Engineering, so I got no help from there.

Ultimately, I'm kinda lost: I know there are two different things being talked about by the Power Quality Analyser and that there is a significant difference between Unbalance and Imbalance so they would use those words to mean two different things even though translating them to Portuguese would give the same meaning most of the times and even though some references take them to be synonym (which also means both words are quite close sometimes).

So, my question is: in the context of Electrical Engineering what is (Voltage and Current) Unbalance and (Voltage and Current) Imbalance? Are they actually different or are they actually synonyms (and what happened was that the power quality analyser manufacturer created a private, different value and called it by another but related name?) If they are different, what is the formula for calculating each of them? And even more importantly (although maybe this is not the right place) what is the correct equivalent names of them in Portuguese?

P.s.: a note in the user guide says:

Imbalance is the rms deviation calculation per channel if the instrument is in Standard PQ Mode. It will display the ANSI definition of unbalance for channels A, B and C if the selected monitoring mode is other than EN50160. When monitoring under EN50160 mode, Imbalance will be a simple value as per IEC definition, defined as the sum of negative sequencing components divided by the sum of positive sequencing components (similar to meter readings under Meter Mode).

and

Supply Voltage Unbalance: The unbalance of a three phase supply voltage onsists of a loss of symmetry of the phase voltage vectors (magnitude and/or angle), created mainly by unbalanced load.

Unfortunately I'm new enough in the field to not know how to deal with this information!

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I'm not sure there is a precise definition for you, and if there is it's likely not well known enough to be applied accurately.

To me the difference is:

Unbalance describes a change, meaning it was balanced and it is now not currently balanced. It's primarily a verb, by doing it you cause something to be out of balance. But it is also a noun (unbalanced) and in that form is synonymous with imbalance.

Imbalance describes the state of being not in balance, it may, or may not be desirable. This is a noun, not a verb, though some may incorrectly use it that way.

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