A rotary phase converter, abbreviated RPC, is an electrical machine that converts power from one polyphase system (including frequency) to another, converting through rotary motion. Typically, single-phase electric power is used to produce three-phase electric power locally to run three-phase loads (any industrial machinery with three-phase motors) in premises (often residential or consumer) where only single-phase is available.
The rotary phase converter is virtually always a less expensive alternative to this approach because it completely eliminates utility installation charges and does not require a new 3-phase service panel. It can usually be installed right off an existing 1-phase circuit at the main service. In addition to those savings, a phase converter may afford substantial savings on utility bills by eliminating the typical demand charges that accompany most 3-phase services.