# Homework Help: How to calculate power

1. Jan 18, 2016

### TurboST2

1. The problem statement, all variables and given/known data
I need to calculate the power given the RMS values for voltage and current.

208 V line to line was put into the system. I measured the following data:

VA magnitude (v) = 119.9
VA angle (degrees) = 0
IA magnitude (A) = 12.1
IA angle (degrees) = -48.4

VB magnitude (v) = 119.5
VB angle (degrees) = -124.4
IB magnitude (A) = 12.2
IB angle (degrees) = -167.7

VC magnitude (v) = 119.2
VC angle (degrees) = 117.3
IC magnitude (A) = 12
IC angle (degrees) = 72.2

I believe the VA and IA values are the RMS values for voltage and current. I was given that VAN (rms) is about 120 (V) which is what was measured for the VA magnitude.

I need to fill out the table shown below.

α, VA'N, VB'N and VC'N can be ignored, I have the values for those columns.

2. Relevant equations
PA = VA*IA
Ptotal = PA + PB + PC
3. The attempt at a solution

This is what I think the answer is for each column and how I got it
IA = 12.1 (A) from measured data
VAN = 119.9 (V) from measured data
PA = VA*IA = 119.9*12.1 = 1450.79 (w)

IB = 12.2 (A) from measured data
VBN = 119.5 (V) from measured data
PB = VB*IB = 119.5*12.2 = 1457.9 (w)

IC = 12 (A) from measured data
VCN = 119.2 from measured data
PC = 1430.4 (w)

Therefore, Ptotal = PA + PB + PC = 1450.79 + 1457.9 + 1430.4 = 4339.09 (w)

2. Jan 18, 2016

### Staff: Mentor

Can you think of a reason why the phase angles of the each value might be important?

3. Jan 18, 2016

### Staff: Mentor

This is so similar to your earlier thread that you could have continued in that same thread. The formula for 3 phase power remains the same.