A three-phase AC voltage regulator is for adjusting a line voltage on
transmission lines. The three-phase AC voltage regulator includes a
sampling circuit, a reference-voltage circuit, a comparator, a switch, a
power supply, and a compensator. The sampling circuit is for sampling the
line voltage. The reference-voltage circuit is for receiving a
line-to-line voltage from the transmission lines and generating a
standard voltage. The comparator is for comparing the line voltage and
the standard voltage to obtain a signal. The switch is for being turned
on or off based on the signal. The power supply is for supplying various
electric powers to the compensator. The compensator is for receiving the
electric power and generating compensating voltages. The compensating
voltages are used to compensate the line voltage.