quote:-->"Written-Pole motors differ from conventional motors in the way the magnetic field is developed. In a conventional motor, the poles are in fixed positions. In a Written-Pole motor, a magnetic layer is written in different places on the motor's poles as the rotor turns.
Written-Pole motors are available in sizes from 15 to 75 horsepower. They are totally enclosed and fan-cooled. With high starting-torque characteristics they run at true synchronous speed.
Varying the magnetic poles during startup gives the motor its slow-starting, high torque characteristics. A squirrel cage winding in the motor also adds induction torque for starting."
this quote is from "http://www.es.wapa.gov/pubs/esb/98Feb/at_motor.htm"
I just made a google search for Written Pole Motors and found that this is a rather cool new technology, although simple.
The main points are: Single phase (up to 100 HP/75 kW) which makes it possible to run in North American homes and farms without 3-phase converter. (That should save some money)
High starting torque but low inrush current (it picks up speed slowly). Insensitive to voltage sags, which means that it should work well on the substandard single phase lines found in developing countries.
Another cool feature is that the power factor is at or near unity, which should allow smaller circuits and transformers.
The only thing it doesn't promise is low weight and small size, which hints that it is heavy and bulky. (A 30 hp 230V motor weighs 300 kg. Does anybody know the weight of a 30 hp 3-phase?)
there is no significant difference in the weights, as there are similar windings in both kinds, only the written-pole's configuration is much different. the nema frame sizes are the same. the biggest difference i can see is the price. the written-pole motor is significantly more expensive, (maybe 5 times as much as a standard motor), but the manufacturer promises the prices going down, as production problems are worked out and the market expands. they are available to the public now, up to 75 h.p., but are still considered in the "prototype" and "development" stages. next on the horizon, according to Precision Power, (the patent-holder), are 100, 125, and 150 h.p. motors. btw, i am looking at becoming a midwestern distributor for this technology.....
yes, 480v. single-phase is not real common in most industrialized areas, but one place it is, is in the oil fileds and mining industries. also, the monstrous commercial farms, such as the imperial valley area of california. these larger horsepower motors awill be offered as an alternative to the diesel power units used to drive big irrigation and dewatering pumps. i havent seen much cost analysis data yet, but what i have seen seems to be more cost-effective, using the new technology, compared to running three-phase power or dealing with the inherent problems of diesel power. once the initial installation of the transformer, controls, and motor set are completed, you can pretty well just turn it on and forget about it; i.e. relatively low maintenance compared to the diesel.