MHB Drawing vectors according to the phase

[aruwin]

Hi! Ok, I got another question here. I don't understand how to draw the vectors. This is a method to simplify analysis of unbalanced three-phase power systems but I just don't understand the drawing here. Do you think you can explain how? I understand how to draw the vectors for Ia, but not for Ib and Ic. For Ia it's really easy, just draw all of them according to the phase but for Ib and Ic, they seem a little different. I know it's got something to do with the coefficients in the equation but I don't know how to draw according to that, though.

 

[DavidCampen]

I am having trouble reading the subscripts - about the only one I can discern for certain is Ia but the drawing is adding (or subtracting) vectors. The vectors to be summed are placed with one starting at the origin and all the others head to tail (the origin of the second vector is at the head of the 1st vector); then a vector drawn from the origin to the head of the last component vector is the sum.