The problem I am working on is:
A 480 V, star connected, three phase ac generator supplies power to a delta connected load through a transmission line. The per phase impedeances of the load and of the transmission line are (16+j20) and (1+j20) respectively. Determine:
(a) The line current
(b) The magnitude of the line to line voltage across the load
(c) The efficiency of the transmission

For a I have I=480/(1+j20)=1.197-j23.94
but should I instead add both impedances together and divide 480 by them?

 

For a I have I=480/(1+j20)=1.197-j23.94
but should I instead add both impedances together and divide 480 by them?

Yes, to find the line current you have to consider the total load plus line impedance - not just the line impedance. You may find it simpler to refer everything back to a 'per phase' representation. In that case calculate the generator line-to-neutral voltage and apply this to the line impedance plus the delta load impedance converted to its star equivalent. Remember the total impedance is a complex number addition. The subsequent complex division of the line-to-neutral voltage by the total line + load impedance will give you the line current.

The rest is complex number manipulation.

%Efficiency=(Real Load Power)/(Real Generator Power) expressed as a percentage.

 

Thanks for the advice,

What I did was:
Vln=480/sqrt(3) <-30 = 277.13 <-30°
Zy=ZΔ/3= (16+j20)/3 = 5.3+ j6.67 <== Not sure why it needs to be converted to ZΔ

Ztotal= (5.3+j6.67)+(1+j20)= 6.3+j26.67

Iline= (277.13 <-30°)/(6.3+j26.67) = (240-j138.57)/(6.3+j26.67) = -2.9 - j9.69

This doesn't seem right to me though

 

Your answers look fine.

Zy=ZΔ/3= (16+j20)/3 = 5.3+ j6.67 <== Not sure why it needs to be converted to ZΔ

So how would you have otherwise determined the total load seen by the generator?

 

Ahh makes sense, does the work that I showed look like I'm on the right track?

 

Ahh makes sense, does the work that I showed look like I'm on the right track?

Yes - it looks fine by me.