Rotary Frequency Converters

Rotary Construction

60 to 50 Hz · 50 to 60 Hz · 60 to 60 Hz Isolation · 50/60 to 400 Hz

60 to 50 Hz – Testing Products for export to 50 Hz countries.
Operating 50 Hz Machines from 60 Hz U.S. utility power.

Importing a machine or an entire factory.

50 Hz to 60 Hz – Operating 60 Hz machines in a 50 Hz country.
Moving a machine or an entire factory.
50Hz to 60Hz power converters are used in 50Hz countries to test products to be exported to the USA.
50 or 60 Hz to 400 Hz – Aerospace applications

Rotary Design



  • Motor Starting Surge
  • Audible Operating Sound Level
  • Vertical vs. Horizontal Construction

Rotary Accessories

  • Digital Output Meter Package
  • RS485 Data Log for Export Testing
  • Enclosures (Outdoor and Indoor Quietizing)
  • Containerization
  • Distribution Panels


A brushless motor and generator are mounted side-by-side (vertical one atop another to minimize footprint is an option) on a welded steel frame skid. This design (as opposed to solid state full sine wave design) is recommended because:

  • Rotary frequency converters are inherently less expensive for 3 phase units 12KVA or larger. A similarly rated unit would be about 50% higher in price and, because of the comparatively limited motor starting capability of solid-state designs, a unit with the same motor starting surge rating would be about twice as expensive.
  • Rotary Design is easier to repair in the field and has far fewer components that are subject to failure and subsequent search for replacements that are no longer made. Any fair-sized city worldwide has a motor repair shop capable of repairing rotary units and electric motors are commonly many years old before the repair shops see them. Should the occasion ever arise, we have our own list of authorized repair shops, and 1 or 2-day turnaround is the rule. Many rotary frequency converters still running in the field are 25 years old or more.
  • Rotary frequency converters are more rugged and flexible in the loads they can handle aside from greater motor starting surge capacity. For example, SCR loads and welders are almost insurmountable problems when using a solid-state approach.
  • Brushless induction motor–low slip, high efficiency, 1.15 service factor
  • 3 phase only for 12KVA and larger sets. For sets 12KVA and over. input any 3phase voltage. Medium voltage (3300V, 4160V. and up for sets over 500KVA)
  • Speed 1000 to 1800RPM up to 1000KVA, 600RPM over 1000KVA
  • Brushless synchronous generator, 1000 to 1800RPM ( 600RPM optional over
  • Voltage 90V. to 575V., 1 or 3 phase, 12 wire reconnectable, the medium voltage also available
  • Solid State automatic voltage regulator holds voltage constant within +/- 0.5% from no load to full load. Voltage setting adjustable by a potentiometer mounted on control panel door +/- 10% of nominal voltage.
  • 15 models from 5KVA to 156KVA and 14 models from 156KVA to 2000KVA
    Control Panel

Control Panel

Unit mounted (on the same skid above the MG set) or for remote panel installations, wall-mounted or free-standing – see discussion of operation noise below. The control panel consists of a NEMA 12 electrical enclosure containing a motor starting assembly with overloads (wye-delta reduced voltage for motors 50HP and up) stop-start push buttons, motor on light – generator output voltmeter, ammeter, frequency meter (with a phase selector switch for 3 ph), 0.5% automatic voltage regulator with panel door mounted voltage adjustment potentiometer and molded case output circuit breaker. With unit-mounted controls, the installer has only to connect the input power to the control panel – the output power is then available at the circuit breaker terminals.

Audible Noise:

Rotary frequency converter units above 30KVA may exceed 83dBa at 3 ft. and, if people are nearby, that may present a problem. There are three approaches to solving the problem listed in order of cost (lowest to highest):

  • The control panel may be specified as separate (not mounted on the skid) and the controls located near the operators with the unit located in another room with other “noisy” equipment. No additional charge.
  • Sound attenuating buffer to bring the sound down to below 83dBa at 3ft. Reasonable added cost.
  • Specify an optional (extra cost) ventilated sound-attenuating indoor cabinet enclosure – with a sound level of 73 dBa at 3ft. maximum.

Want to know what a given dBa level sounds like?

Typical Open Horizontal Construction

6.25 to 25KVA | 6i65-1

Note: Control Panel mounted and prewired on the same skid as rotary components require only bringing utility power into the control panel to result in output power available on output load contacts of the circuit breaker inside the panel

  • Typical dimensions: 40 to 45″ Wide X 25 to 28″ Deep X 35″ High
  • Weight: 550 to 1000 lbs.

Operating dBa 76 to 78 @ 3 ft. is not objectionable in most industrial environments. In lab environments, the motor generator set can be stationed in an equipment room while the control panel outfitted with all the start-stop controls, meters, voltage adjustment, and output circuit breaker terminals would be wall mounted in the lab itself. In extreme cases, ventilated sound-attenuating enclosures are available.

30 to 125KVA | 6i65-1

40 KVA with Control Panel separately mounted to isolate rotary components for noise control

100KVA with skid-mounted control panel

100KVA Control panel – Door open to show output circuit breaker and WYE-DELTA motor starter

Options available at an extra cost include:

– Outdoor Enclosure with anti-condensation motor and generator coil heaters.
– Control Panel outdoors in the enclosure or mounted indoors.
– Open Vertical Construction – to minimize the footprint

  • Quietized Vertical Construction – see below, Enclosed Quietized Vertical Construction.
  • Synchronous Motor – for +/- 0Hz operation

– For dimensions and weights, call or fax the factory.

156 to 375KVA | 313i6050

Units of this size require special baffling to meet OSHA requirements. Shown here is the 313KVA unit with sound baffles (83dBa @ 3ft.). Without baffling the noise level is 97dBa. Cost can be reduced with a remote panel location at no extra charge.

Options available include:

  • Quietized Vertical Enclosed Construction – less than 75dBa at 3ft.
  • Typical Open Horizontal Construction
    – Gearbox Type 400 to 2000KVA
  • Optional Sound Reducing Enclosure

Quietized Cabinet

To receive a list of various countries and the standard 1ph / 3ph voltages and frequencies for each contact us today.

Pictured is a 62.5KVA unit enclosed in a 14ga. enameled steel, ventilated enclosure with sound attenuating foam.


We are here to help, contact our team

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