<P> A rotary phase converter is a three - phase motor with special starting arrangements and power factor correction that produces balanced three - phase voltages . When properly designed, these rotary converters can allow satisfactory operation of a three - phase motor on a single - phase source . In such a device, the energy storage is performed by the inertia (flywheel effect) of the rotating components . An external flywheel is sometimes found on one or both ends of the shaft . </P> <P> A three - phase generator can be driven by a single - phase motor . This motor - generator combination can provide a frequency changer function as well as phase conversion, but requires two machines with all their expenses and losses . The motor - generator method can also form an uninterruptible power supply when used in conjunction with a large flywheel and a battery - powered DC motor; such a combination will deliver nearly constant power compared to the temporary frequency drop experienced with a standby generator set gives until the standby generator kicks in . </P> <P> Capacitors and autotransformers can be used to approximate a three - phase system in a static phase converter, but the voltage and phase angle of the additional phase may only be useful for certain loads . </P> <P> Variable - frequency drives and digital phase converters use power electronic devices to synthesize a balanced three - phase supply from single - phase input power . </P>

What is 3 phase power vs single phase