Rotary Phase Converter - Design

  PhaseMAXX - (Trademark - Canada / USA)


PhaseMAXX rotary phase converters are actually single-phase machines that develop not just one, but two additional phases - each of which are progressively displaced in time-phase sequence by 120 degrees. 

Because each of the two manufactured phases are a result of back emf, the time-phase sequence is subject to a small variation dependent mostly on rotor speed, mechanical placement of field coils, and circuit impedance. PhaseMAXX incorporates a proprietary feature that corrects this variance. The result is a machine that provides 3-phase power where each of the three output phases are displaced by 120 degrees.

Frame size is a critical factor in determining  phase converter selection for a particular load. But PhaseMAXX rotary converters are considerably more than just a "pretty face" in a large frame.

An engineered rotary phase converter resembles a standard 3-phase induction motor (without the output shaft), but is internally quite different. The converter rotor (rotating component) can be designed and centrifugally cast to effect a high cage resistance - unlike that of the conventional low resistance rotor supplied in NEMA design "B" 3 phase motors. The high resistance rotor provides the converter with low starting current - initially required because the converter FRAME is much larger than that of the largest motor it can provide 3-phase power for. And, because Utility companies all have restrictions on the highest Locked Rotor Amperage they will allow on their power grid, prudent phase converter manufacturers ensure that the Locked Rotor Amperage of any rotary converter does not exceed this restriction.

Several other differences between Rotary converters and Electric motors exist. A Rotary converter which is produced with a high resistance rotor, yet has no other difference from that of the standard 3-phase motor, will not be able to maintain an angular phase displacement of 120 degrees between each output phase (the same as a Utility supplied 3-phase supply). The result of a converter system that operates in this fashion, is a higher electric motor operating temperature, reduced motor efficiency, and drastically reduced motor life. Again, prudent converter manufacturers design either (converters that have a unique rotor cage capable of maintaining phase angle displacement), or (converter stationary windings with unique placement or provision for the adjustment of phase angle for specific loads).

While some individuals may suggest taking a standard electric motor and "jury rigging" something resembling a rotary converter, such action will inevitably result in a simulation of a 3-phase supply which cannot provide full rated HP for any motors connected to the system. At best, (where such a device is even successful in starting an electric motor) it will not operate the motor within the motor's specification. With a little closer inspection, it can be seen that load motors will suffer as a result of severe current imbalance and higher heat loss due mostly to the variation in voltage magnitude and phase imbalance. 

Proprietary information / M. J. Fortin (EM) - PhaseMAXX Power Products Group.

PhaseMAXX is a trademark registered in Canada and USA.

For additional information as relates to [NEMA frame assignments] and their application to phase conversion, select the associated drop down menu button located at the top of this page.

For information related to [Diversity Factor] and the role it plays as a selection criteria for phase conversion, select the associated drop down menu button located at the top of this page.


Electram Rotary Equipment Ltd.
Edmonton, Alberta, Canada

Part of the PhaseMAXX Power Products Group