I have come across an unusual part of a circuit that I hope someone could shed some light on and I have redrawn in LTSPICE. The circuit is to measure voltage of a 3-phase generator. Two of the phases R and S are measured and applied to the rectifier shown below. The "+" and "-" are then fed into a differential amp. It is unusual to see the second phase applied to the lower half of the circuit shown.
Why would this configuration be used and is there any advantages/disadvantages to using it this way.