1. The problem statement, all variables and given/known data
hello everyone
I'm a little confused with the whole 3- phase system.
for example:

I tried solving using differenet methods we were taught, but every way i try i get a different result.

For example: 1) I thought that the wattmeter will measure the Real Power of a single load, which should be a third of the total Real Power of the motor. so:

on the other hand:

I'm starting to feel lost in this, so any help would be appreciated.

P.S. Maybe I should have done a Y-DELTA transformation? Although I'm not sure what good would that do...

A wattmeter connected as described will sense the voltage of each phase of the motor, but it will sense more than the current of a single phase of the motor, it will sense the phase current x √3.

With this correction, does that confirm your analysis?

What you calculated in the first step is the power in one phase of the motor. You will want to multiply this by √3 to compare it with your second calculation.

Where you write V_{RS} / Z I think there is a missing √3.

and a warm greeting ..... http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

Sadly, Im still unsure of what I am doing wrong.
This is my understaing of the setup:

To my understanding, in a delta configuration (such as shown),
V_{LINE}=V_{PHASE} , so wouldn't that mean that I_{PHASE}=[itex]\frac{V}{Z}[/itex]? where does the √3 come from (if I want to use the power formula I mentioned in the first solution)?

BTW it has come to my attention that this question was originally a multiple-choise question.
The possible answers were: A. (-44.03) B. 22.07 C. (-14.68) D. 66.21 (all in [kW])
bit I have no Idea which is the correct one.

A wattmeter has 2 pairs of sensing coils, one for voltage and another for current. I think it is unreasonable to believe you can routinely break open a delta motor and connect something in series with one of its phases to sense phase current!

You performed 2 calculations. Basically, the first is for 1/3 of the motor's power. The second is for 1/3 of (√3 of the motor's power).

My contention is that the best you can do is to have the wattmeter measuring the latter (whether you like it or not), sensing V_{RS} and I_{R}. You can't sense the motor's phase current, even if you wish you could. Well, that's my thinking.

So it looks like the construction brings out the ends of each motor phase so that you can connect a meter in series with a single phase of the motor to meter the phase current! (Or at least it is intended to represent that.)