170508-1640 EDT
Forget getting hung up on the word neutral.
What KY Solar wants to do is to create a way to connect his solar inverter(s) to the power company system such that he can transfer power to the utility, but do this at a somewhat reduced voltage level to avoid having his inverter trip on overvoltage.
His inverter must connect to a nominal 240 V center tapped single phase system. This sysrem center tap is also called the system neutral, and is also grounded, but being grounded is irrelevant to his problem. The neutral is only needed as a voltage reference to the inverter.
There are many ways to provide these lower voltage entry points. They all envolve subtracting a voltage from each hot line that is synchronized to line voltage frequency and phase. The simplest is to use one or two transformers.
One method uses a special autotransformer. This transformer consists one single winding with four terminating points, the two coil ends and two taps. This one coil is all wound in one direction on a single core. I will use T for terminal instead of Xs or Hs.. T1 is one end of the coil and connects to one power company hot line. T2 is a tap at a 12 V point and goes to one of the inverter hot lines. T3 is a tap at 240 V minus 12 V and goes to the other inverter hot line. In other words the nominal voltage between T2 and T3 is 240-24 = 216 V. And last T4 goes to the other power company hot line.
By virtue of the center tap on the power company transformer the voltages on T2 and T3 relative to the center tap (neutral) will be nominally 120-12 = 108 V.
This special transformer must use wire large enough between T1 and T2, and T3 and T4 to handle the full output current of the inverter. The transformer wire between T2 and T3 only has to be large enough for the sum of the reflected currents going to the outer coils.
There is no neutral in this transformer, and the equivalent neutral point should not be brought out and connected to power company neutral. The transformer might be easily burned out. Thus, I change my statement in an earlier post that the H2H3 could be connected to power company neutral. Study the circuit to see why.
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