niffur said:I think what is missing here is the actual maximum load current. We can talk buy/sell current all we want but ultimately the inverter can be producing more current than what is in shortage or excess. All that current would flow on the neutral.
niffur said:I think what is missing here is the actual maximum load current. We can talk buy/sell current all we want but ultimately the inverter can be producing more current than what is in shortage or excess. All that current would flow on the neutral.
tallgirl said:Here's a picture --
http://forums.mikeholt.com/attachment.php?attachmentid=2006&stc=1&d=1215874649
Red is neutral current, blue is load, green is inverter output.
crossman said:The attachment is not working for me.
tallgirl said:I'm not sure his diagram is either useful or correct. I've been trying to make sense of it since I saw it and it seems to include an incorrect assumption, as well as just plain being wrong.
tallgirl said:The setup for a standard grid-interactive inverter is that the voltage sources are on the "same side" of the load
tallgirl said:power from the PoCo passes through the inverter on the way to the load.
tallgirl said:This is a 120/240 setup -- dual inverters. In which case neutral current is the sum of the maximum load plus the maximum inverter output.
crossman said:But Tallgirl's statement was concerning the wiring which is coming from the utility transformer. If there is 5 amps sell on one leg and five amps buy on the other leg, there is 10 amps total on the neutral going into the centertap, regardless of the actual connected load and regardless of how much current the inverter is putting out.
crossman said:Niffur, the problem here is that the currents are not opposing. One is a "buy" and one is a "sell". This negates the old rule of "the neutral carries the imbalance of the two currents".
Certainly, if both currents are "buy", then the two five amp currents results in zero on the neutral. But a "sell" situation on one leg means this current is going backwards and you would add, not subtract.
Disclaimer: I am taking a simplistic approach and using all positive currents. The old "imbalance" formula will work if we use "negative" currents.
crossman said:Without an inverter, and with a 120/240 single phase system, it is going to be impossible to overload the neutral of a code-compliant installation by any type of switching the loads on and off during certain periods in the sine wave.
Now, on a three-phase wye, I am totally in agreement with you.
Back to the 120/240 single phase service with inverter.... I am sticking with the point that it is impossible to overload the neutral of a code-compliant installation no matter what loads are on or off.
If I am incorrect, I am certainly open for an education. Convince me I am wrong with diagrams, theory, etc.