An advantage of machines or equipment that require a single phase electric supply is they can be run where there is a sufficiently rated single phase electrical supply. Disadvantages of single phase is the cost of conductors to transmit sufficient power to heavier motors or machinery. With a single phase electrical supply, as current alternates, the supply of power changes direction of flow. The effect of this is a varying pressure of electricity where electricity changes flow direction. Electrical pressure (voltage) drops to zero volts as the flow changes (alternates). In the U.S., electricity is generated at 60hz. (cycles per second) A single phase electrical supply cycles 60 times per second. It drops to zero volts twice per cycle.
When a machine requires a three phase electrical supply to operate, an option for the machine owner is to use a three phase rotary converter to take single phase input and convert it to three phase output. Delivery of three phase power is more efficient than single phase. Each of three conductors not only supply current, they function to return current from the other two conductors. With a three phase electrical supply, there is the potential to transmit three times more power with only one additional conductor (wire) compared to the two wires used to carry current in a single phase electrical supply.
For a location where three phase equipment or machinery will be used and only single phase service is readily available, using a three phase rotary converter may be the answer. Three phase motors are smaller, can smoothly and more efficiently deliver the same horsepower as larger single phase motors.