Rotary Frequency Converters
(also called "Motor-Generator Sets" or MG Sets")

Rotary frequency converters convert incoming AC Power into rotary mechanical power (spinning motor), which transmits its rotary power to a generator, which converts its mechanical power into Electric AC output power. Rotary power is often described in terms of Horsepower, while Electrical power is described in Kilowatts (kW) or Kilovolt-Amperes (KVA). The conversion of frequency (hertz – Hz), voltage, and/or phase (3 phase, 1 phase) are inherent in this process.

Motor Generator sets use several methods of coupling the drive motor to the generator. The simplest and least expensive method is belt coupled converters that use drive belts and pulleys to not only transfer the energy from motor to generator, but also change the frequency by pulley ratio. Another method is direct coupled converters that directly couple the motor shaft to the generator shaft using a mechanical coupling, and adjusting the speed of the drive motor to vary the rotational speed of the generator, thus varying the output frequency. An adjustable speed electronic drive (ASD) is used for this purpose, instead of a conventional motor starter.

Finally, the most sophisticated and most costly method is to build the motor and generator onto a single common shaft, called common shaft frequency converters. In this case, the frequency change is made by winding the motor with a different number of electrical poles than the generator. For example, a 12 pole motor and 10 pole generator will yield a 60-to-50 Hz conversion.

In certain applications, only power line isolation (complete electrical discontinuity, input to output) or power line conditioning (poor incoming electrical power converted to good output power), is required. In these power line isolators, an insulated flexible coupling is used between motor and generator, to transmit the power from motor to generator, and completely isolate the input from the output. Typically, no change is made to the frequencies, although phase or voltage conversion may be required.

Build your own partTypical Characteristics OF Rotary Frequency Converters

  • More attuned to larger applications 10 KVA plus
  • Much better at starting motor loads
  • Rugged floor mount construction
  • Generally, fixed output frequency
  • Costs do not increase linearly with power; e.g., 3x power = 1.5x cost
  • Harmonic distortion and noise on input power is not passed to the output
  • Can source heavy overload currents 2-4X for short periods of time
  • Full load efficiency up to 90+% on large units

Rotary Frequency Converters: Belt-Coupled Motor Generator Sets
ROtary Frequency Converter: Belt Coupled
  • Economical & best value
  • Connected by belts/pulleys
  • Power ratings 1-500 KVA
  • Complete electrical isolation from harmonics, spikes.
  • High efficiency induction motor
  • Synchronous generator w/voltage regulator.
  • Tight frequency regulation (+/-1%)
  • Waveform: THD < 5%

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Rotary Frequency Converters: Direct Coupled Motor Generator Set
ROtary Frequency Converter: Belt Coupled
  • Direct coupling of motor and generator shafts
  • Allows for parallel operation
  • Gen set power ratings 1-500 KVA for individual units
  • Power ratings to 2500 KVA in parallel
  • High efficiency induction motor
  • Synchronous generator w/voltage regulator
  • Tight frequency regulation (+/-0.3%)
  • Waveform: THD < 5%

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Rotary Frequency Converters: Common Shaft Motor Generator Set
ROtary Frequency Converter: Belt Coupled
  • Precision; exact frequency output
  • Highest reliability
  • Power ratings: 1-1000++ KVA
  • Complete electrical isolation from harmonics, spikes.
  • Low maintenance.
  • Synchronous motor
  • Synchronous generator w/voltage regulator.
  • Waveform: THD < 5%

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Rotary Frequency Converters: Power Line Isolator & Conditioner
ROtary Frequency Converter: Belt Coupled
  • Complete isolation between the load and input power
  • Power ratings: 2.5 to 500 KVA
  • Maintains approx. 100 milliseconds of ride-through during power outages.
  • High efficiency induction motor or synchronous motor
  • Synchronous generator w/voltage regulator.
  • Waveform: THD < 5%

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