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Arotary phase converter, abbreviatedRPC, is anelectrical machine that converts power from onepolyphase system to another, converting through rotary motion. Typically,single-phase electric power is used to producethree-phase electric power locally to run three-phase loads in premises where only single-phase is available.
A rotary phase converter (RPC) may be built as amotor–generator set. These completely isolate the load from the single-phase supply and produce balanced three-phase output. However, due to weight, cost, and efficiency concerns, most RPCs are not built this way.
Instead, they are built out of a three-phase induction motor or generator, called an idler, on which two of the terminals (the idler inputs) are powered from the single-phase line. Therotating flux in the motor produces a voltage on the third terminal. A voltage is induced in the third terminal that is phase shifted from the voltage between the first two terminals. In a three-winding motor, two of the windings are acting as a motor, and the third winding is acting as a generator. Since the third, synthesized phase is driven differently from the other two, its response to load changes may be different causing this phase to sag more under load. Since induction motors are sensitive to voltage imbalance, this is another factor in de-rating of motors driven by this type of phase converter. For example, a small 5% imbalance in phase voltage requires a much larger 24% reduction of motor rated power.[1] Thus tuning a rotary phase converter circuit for equal phase voltages under maximum load may be quite important.
Rotary phase converters are used to produce a single-phase for the single overhead conductor inelectric railways.[citation needed] Five European countries (Germany,Austria,Switzerland,Norway, andSweden), where electricity is three-phase AC at 50 Hz, have standardised on single-phase AC at15 kV 16+2⁄3 Hz for railway electrification; phase converters are, therefore, used to change both phases andfrequency. In theSoviet Union, they were used on AC locomotives to convert single-phase, 50 Hz to three-phase for drivinginduction motors fortraction motor cooling blowers, etc.[2]
