Automatic voltage regulators can be designed for single-phase or three-phase AC applications.
It is common for utilities to use single phase automatic voltage regulators ganged together to provide voltage regulation for three phase. These are often “can-type” units pole-mounted outdoors.
Single phase automatic voltage regulators may also be used where a three phase source is used to supply three single phase loads.
Most three phase AVRs may also be used to feed single phase loads.
For three phase loads, it is usually more cost effective to use a three phase AVR.
A three phase automatic voltage regulator might regulate all three phases together or it might regulate each phase independently, depending on the design of the AVR.
When dealing with three phase power, it is not uncommon to find that one phase has a “high” voltage level while another has a “low” voltage level. In this situation, being limited to regulating the voltage level of all three phases together, up or down the same amount, may not produce satisfactory results.
Independent phase regulation is often the preferred method since it typically provides better phase-to-phase voltage level balance. Large differences in voltage levels from phase-to-phase can cause premature failure of electrical devices due to overheating or vibration.