Graffeo 26 and graffeo 27

[Wow_PE!]

I can follow Graffeo’s example 26.  The problem asks you to find turns ratio given primary voltage and secondary voltage.  It says to divide the wye side voltage by sqrt3  to get phase voltage before calculating the ratio.

However the next problem is very similar, but it seems the delta wye is not accounted for?  I’m confused.

 

[Wow_PE!]

Actually now that I think about it, in the second problem , the sqrt3 cancels out.

V1/v2 = i2/i1

for the wye

vline = vphase * sqrt3

and for the delta

I_line = I_phase * sqrt3 

 

[FelizEng PE]

Yes you are correct. 

What I do is convert all Voltages & Currents to their phase values and apply: 

V1/V2 = I2/I1 

And hence solving for Vtransmission line:

Vline (on Wye-side of TX1) = sqrt(3) * 12.47kV *[1130.36A/(122.57A*sqrt(3))]

The root 3's cancel out and you are left with

Vline = 12.47kV * (1130.36A/122.57A)