symmetrical components

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PG1995

Active Member
Hi

Are the negative sequence and zero sequence networks used in symmetrical components method real? I understand that the word 'real' is a bad choice here and somewhat subjective, and one could also ask similar questions like 'if Fourier series harmonics are real', 'if flow of electron current is real as mostly visualized', 'if negative frequencies real', etc. At least to me, harmonics, electron current, and negative frequencies are real in one way or another. Perhaps, they seem 'real' because I have become used to them. But on the other hand negative and zero sequence networks are new thing for me.

Why does a balanced three phase system only contain positive sequence components? It's said that counter clockwise rotation of generator produces positive sequence voltages. It might be possible that even in a balance system negative and zero sequence voltages are present but they get cancelled in some way for a balanced system but become prominent in case unbalance condition when their cancellation cannot occur. Thank you.

1: https://www.gegridsolutions.com/smartgrid/Dec07/7-symmetrical.pdf
2: https://www.researchgate.net/post/W...tem_contain_only_positive_sequence_components

Colin

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cowboybob

Well-Known Member
Seems to me it all rests on the physical conditions (direction of rotation) of the generator and the motor, i.e., normal or reverse, or "no fault" or "fault").

I liked this simplification:

"Al-Motasem I Aldaoudeyeh
North Dakota State University
The simplest example is to think about a resistor. The resistor will have a specific resistance value even if it is not in a circuit. Such resistance is simply determined by resistivity, cross-section area, and length. The resistance here is a parameter that determines the value of an output variable (current through it) for a given input variable (voltage across it).
You may extend the idea to inductors as well. Inductance (parameter that exists even if inductor is not inside a circuit), current (input variable), and flux linkages (output variable)."

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