Negative & Zero sequence currents

http://www.eng-tips.com/faqs.cfm?fid=314

I don't understand this, but, this is the Symmetrical components page from Wikipedia.

It is not too difficult to understand .

Any unbalanced three phase system (or for that matter balanced too) will have the three phase (say voltage) - of un-equal magnitude (or say amplitude) and they will not be equually spaced in time (ie the phasors will not be 120⁰ shifted rather it will be shifted by some other angle)

Right?

Now we do not like that behavious, we like things to be symmetric, that helps us in our calculation.

So what we do is we try to convert this three phase system into a set of other three phase systems such that their superposition gives us the current system

The zero sequence part is the one that is common to all the three.

The positive sequence is similar ie the three phases at 0^o, 120⁰ and 240^o (called sequence ABC)

The negative sequence is opposite to it ie at 0^o, 240⁰ and 120^o (call it sequence ACB)

Now obviously

Voltage of phase A = the sum of three at zero ie V₀+V₁+V₂

But for B we have to rotate these ie = V₀(common to all) + V1 (Rotated back by 120 deg ie rotated forward by 240 deg) +V2 (rotated forward by 120 deg)

and for C it is = V0 + V1 (rotated forward by 120) and V2 (back by 120)

That is what is in the matrix.

rest is the inverse to find the values of the sequences.