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Interconnection scheme of positive and negative sequence networks

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Krustabas

Electrical
Joined
Nov 5, 2008
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22
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LV
I'd like to ask if anyone knows how to form an equation shown in the attached figure (from US4559491 patent).

In the image there is an expression for a phase R current at a point A for a phase-to-phase fault:
IR = (a^2 * I1R + a * I2R + a^2 * Ipre-fault) * a (1)

I can't figure out why (1) is so complicated because in general case phase R current is constructed from symmetrical components as:
IR = I1R + I2R + I0R (2)

For S and T phases there would be also one "a" and one "a^2" operator. Removing zero sequence component and adding a pre-fault phase current I get:
IR = I1R + I2R + Ipre-fault (3)

This is clearly not the same as (1). Am I missing something?

Thank you
 
 https://files.engineering.com/getfile.aspx?folder=953b93ef-d07e-4efa-862e-78baed381457&file=Phase_current_at_point_A.png
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