Voltage Regulators basically is autotransformers that regulate the voltage in medium voltage power lines by boosting or bucking the voltage.
Three single phase voltage regulators can connect in either wye or delta conection in a three phase system.
Specifically in delta conection we can connect the voltage regulators in closed delta or open delta conection.
In closed delta we use three single phase regulators in an ordinary delta conection.
The amazing thing is that we can use just two single phase regulators in open delta conection and have symmetrically voltage raise or decrease in all three phases...!!!
The 1:1 three phase transformer in the circuit is just used in order to have a ground reference point so that we can plot the voltages, because we cannot ground both the source and load in a line that have voltage regulators in open delta conection.
The example shows a voltage drop compensation that is caused from the resistance and reactance of the line.
