Kaplan and Graffeo don't agree

[MTO]

[SIZE=medium]5.2 A balance wye connected load of 8+j6 per phase is connected to a three phase 208V (Line to Line) source. Determine the three line currents. Question do we take the reference angle as <0 or <-30 that is Van = 120.08<-30 or Van=120<0[/SIZE]

 

[jgharris P.E.]

I have been going through the Graffeo book starting last week (for the April PE) so I will take a shot at this:

They state that you have a 3 phase balanced wye load connected to a 208V L-L source. Draw it.

Determine the 3 line currents. Well, there isn't any Zline impedance only Zload which makes this problem easier. We know that the voltage at the terminals of the wye are gonna be the Vll/Vab= 208V @ 0 since they didn't specifiy any angle. To find the Vl-n you need to use the Vl-l= sqrt (3)*Vphase@30degrees.

If you solve for Vphase you should get your Vl-n=Vphase= 120V @ -30 degrees. From there simple ohms law and solve for IL-N=Vl-n/(Zload). Iphase=ILL for wye connected loads.

I got Iab=12A @-67 so since it is balanced just find the 120 and 240 out to find Ibc and Ica.

Hope I didn't steer you wrong. I'm no pro at this but I have been cranking out a few of these problems the past few days...

 

[jgharris P.E.]

I know your main question had to do with the Vl-n angle but I decided to solve it all the way since this is good practice for me.

Also I did not refer to my Graffeo book i went off the information you provided to solve this problem.

Hope I provided more good than harm...

JGH