I need to record kW & kWh for individual phases on a circuit that has a 3 phase power meter that outputs the following data:
Total for all three phases:
- kW
- kWh
- kVA
- kVAr
- power factor
- Frequency (we can assume that this is universal across all phases)
For each phase, L1, L2, L3 the following readings are also available to me:
- Volts (L-N)
- Line Current (Amperage)
Considering that the load distributed unequally, I'm wondering whether there is a way to calculate individual load in kW, using the data that is available to me.
It seems to me that it should be possible to use a ratio calculation to calculate how much of the total load belongs to each phase:
kWL1 = (kVAL1/kVAtot)*kWtot
Can someone confirm this hypothesis?
Best Answer
I don't see any way to do this. You need the power factor of the individual phases and that's not available. The equation is incorrect.
\$P_{actL1} = P_{appL1}\cdot\cos\varphi_1\$
\$P_{act,tot}/P_{app,tot}= \$
\$= (U\cdot I_{l1}\cdot \cos\varphi_1 + U\cdot I_{l2}\cdot \cos\varphi_2 + U\cdot I_{l3}\cdot \cos\varphi_3)/(I_{l1}\cdot U + I_{l2}\cdot U + I_{l3}\cdot U)\$
\$= ( I_{l1}\cdot \cos\varphi_1 + I_{l2}\cdot \cos\varphi_2 + I_{l3}\cdot \cos\varphi_3)/(I_{l1} + I_{l2} + I_{l3})\$
and that is not equal to \$\cos\varphi_1\$.