Rotary phase converter

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 main principles of RPC operation are as follows:

Three-phase induction motors have three terminals called "legs", usually numbered (arbitrarily) L1, L2, and L3.

A three-phase induction motor can be run at two-thirds of its rated horsepower on single-phase power applied to any pair of legs, once spun up by some means.

A three-phase induction motor that is spinning under single-phase power applied to legs L1 and L2, generates an electric potential (and can deliver power through) leg L3, although without some form of current injection, special windings in the idler, or other means the voltage will sag when a load is applied.

Power factor correction is a very important consideration when building or choosing an RPC. This is desirable because an RPC that has power factor correction will consume less current from the single-phase service supplying power to the phase converter and its loads.

Balanced voltage between the three legs of power is important for operational life of the equipment receiving that power. Unbalanced three-phase power can damage the equipment that it is meant to operate.

At the beginning of the 20th century, there were two main principles of electric railway traction current systems:

These systems used serial traction motors. All of them needed a separated supply system or converters to the standard 50 Hz electric network.

Kálmán Kandó recognized that the electric traction system must be supplied by single-phase 50 Hz power from the standard electric network, and it must be converted in the locomotive to three-phase power for traction motors.

He created an electric machine called a synchronous phase converter, which was a single-phase synchronous motor and a three-phase synchronous generator with common stator and rotor.

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