renewablesHI
Member
- Location
- Honolulu, HI, USA
Hello all,
My question today is related to a PV system that utilizes two 120 V inverters with a common neutral that generate sinusiods 180deg out of phase to create a split-phase 240V waveform. The two 'hot' outputs of the inverters, say L1 and L2, and the common neutral are connected across a single phase on the secondary side of a high-leg delta transformer (say A to B). Between the inverters and the xfmr is a three phase smart breaker. There are current probes (CTs) and voltage probes (PTs) on each 'phase' going to the breaker, the values of which are recorded by the smart breaker.
I need to know how to calculate the power coming out of the inverters using the per phase currents and voltages. The inverters are indeed grid-tie inverters and the primary side of the xfmr is connected to the utility. There are more elements to the system on the primary side of the xfmr, yet I am only concerned with calculating the power from the PV inverters.
Obviously, typical three-phase balanced power calculations will not be accurate in this case since one of the phases (say Phase C) is not connected and consequently reads no current by the meter. Summing individual, per phase power calulations seem to get me in the ballpark, yet I don't believe that method is accurate. Another possibility is to say the power is one of the phase current values times the voltage across that phase (P = Ia * Vab), yet I wonder about this also, though it does seem to provide a reasonable efficiency for the PV system.
As an added twist, sometimes the current values reported for Ia and Ib are up to 8A different. I realize this could be a problem with the data collection system, but it could also mean that the current flows through the neutral, which, of course, is not metered.
Does anyone know the correct way to calculate the total power flowing from this PV system or have any thoughts to add?
I appreciate the interest
My question today is related to a PV system that utilizes two 120 V inverters with a common neutral that generate sinusiods 180deg out of phase to create a split-phase 240V waveform. The two 'hot' outputs of the inverters, say L1 and L2, and the common neutral are connected across a single phase on the secondary side of a high-leg delta transformer (say A to B). Between the inverters and the xfmr is a three phase smart breaker. There are current probes (CTs) and voltage probes (PTs) on each 'phase' going to the breaker, the values of which are recorded by the smart breaker.
I need to know how to calculate the power coming out of the inverters using the per phase currents and voltages. The inverters are indeed grid-tie inverters and the primary side of the xfmr is connected to the utility. There are more elements to the system on the primary side of the xfmr, yet I am only concerned with calculating the power from the PV inverters.
Obviously, typical three-phase balanced power calculations will not be accurate in this case since one of the phases (say Phase C) is not connected and consequently reads no current by the meter. Summing individual, per phase power calulations seem to get me in the ballpark, yet I don't believe that method is accurate. Another possibility is to say the power is one of the phase current values times the voltage across that phase (P = Ia * Vab), yet I wonder about this also, though it does seem to provide a reasonable efficiency for the PV system.
As an added twist, sometimes the current values reported for Ia and Ib are up to 8A different. I realize this could be a problem with the data collection system, but it could also mean that the current flows through the neutral, which, of course, is not metered.
Does anyone know the correct way to calculate the total power flowing from this PV system or have any thoughts to add?
I appreciate the interest