# Got a question on 3 phase power

#### purdub

Joined Nov 14, 2006
5
in lecture last week, our instructor gave us an extra credit problem that we had no clue how to solve. i have gotten most of the wye diagram done, and am confused on what to do with the angle at the end.

heres the problem...

A balanced three phase load consisting of 4+j3 ohms per pahse is connected to a 208Y/120V source. Calculate the (1)current per phase, (2)power per phase, and (3)total three phase power for the wye connected load. Repeat for a delta connected load.

for the wye diagram, i got
Ian=41.6A at -36.87 degrees
Ibn=41.6A at -156.87 degrees
Icn=41.6A at 83.13 degrees

Pan=8.65kW at -36.87 degrees
Pbn=8.65kW at 96.87 degrees
Pcn=8.65kW at -23.13 degrees

how do i solve for Ptot? would it be 25.95kW+jQ? and what goes in the place of j and Q?

#### purdub

Joined Nov 14, 2006
5
im not even sure if i did the first 2 parts right now

can someone give me an outline on how to do it?

#### subtech

Joined Nov 21, 2006
123
I'm a little late getting here.
Post again and let me know.........

#### purdub

Joined Nov 14, 2006
5
i eventually figured it out after a lot of reading and calculations

thanks

#### subtech

Joined Nov 21, 2006
123
Although the site is supposedly "for professional engineers only-no students" you can find some interesting reading here- www.eng-tips.com
The electric power engineering forum gets interesting at times.
Be prepared for some abrupt and downright hostile posts occasionally.

#### purdub

Joined Nov 14, 2006
5
i tried posting it there...they didnt like it
also didnt find much helpful info on 3 phase power

#### subtech

Joined Nov 21, 2006
123
I can recommend a couple of super good books that cover 3 phase power, motors, transformers and such if you are interested. Or, if you would care to post some specific questions, I'd be glad to try to help. I should warn you however, I'm not an engineer. I'm a journeyman lineman and a protective relay technician. My math is not on the level of a nuclear physicist.