Calculate Power Using RMS Voltage & Current

  • Thread starter TurboST2
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In summary, the task at hand is to calculate the power given the RMS values for voltage and current. The measured data for VA and IA are 119.9 V and 12.1 A, respectively. Using the formula PA = VA*IA, the power for phase A is calculated to be 1450.79 W. Similarly, for phases B and C, the powers are calculated to be 1457.9 W and 1430.4 W, respectively. Therefore, the total power for the system is 4339.09 W. The phase angles of each value may be important as they can affect the overall power in the system.
  • #1
TurboST2
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Homework Statement


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.
mt5xyd.jpg

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

Homework Equations


PA = VA*IA
Ptotal = PA + PB + PC

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)
 
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  • #2
Can you think of a reason why the phase angles of the each value might be important?
 
  • #3
TurboST2 said:
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)
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.
 

1. What is RMS voltage and current?

RMS stands for Root Mean Square and it is a method of measuring the average value of an alternating current (AC) or voltage. It takes into account the changing nature of an AC signal and gives an equivalent direct current (DC) value that produces the same amount of power.

2. Why is it important to calculate power using RMS voltage and current?

Calculating power using RMS voltage and current gives a more accurate representation of the power being used in an AC circuit. This is because the traditional method of calculating power using peak voltage and current does not take into account the changing nature of AC signals.

3. How do you calculate power using RMS voltage and current?

To calculate power using RMS voltage and current, you simply multiply the RMS voltage by the RMS current. The formula is P = VRMS x IRMS.

4. Can RMS voltage and current be used for DC circuits?

No, RMS voltage and current are only applicable to AC circuits. In DC circuits, the voltage and current values do not change over time, so there is no need to calculate an equivalent DC value.

5. What are the units for power when using RMS voltage and current?

The units for power when using RMS voltage and current are watts (W). This is the same as the units for power in DC circuits.

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