hybrid induction/pm motor may be coming...

[electricpete]

I recently saw a brief presentation from a motor manufacturer suggesting that within a year they will be introducing a line of "hybrid" electric motors which has a squirrel cage for starting only and permanent magnets for running (synchronously). The benefit is that rotor electric and magnetic losses are pretty much eliminated, resulting in much higher efficiency than readily obtainable in an induction motor.

To be offered in standard NEMA frame sizes and also in smaller frame sizes (higher horsepower or lower speed for a given frame size).
Can be run direct on-line start or soft start or vfd although there were some precautions for direct on-line start:
* allowable inertia may be somewhat lower than NEMA standard
* might require special coupling to avoid destructive oscillating system torque during start
* presenter didn't know how the starting current would compare to standard NEMA design B induction motor.
* presenter didn't comment on the pullout torque capability or temporary overload capability

I thought I'd share, but unfortunately I have no link. (thought I could find something on google, but no dice).


=====================================
(2B)+(2B)' ?

 

[jraef]

This is not new. Google "IPM" (Internsl Permanent Magnet) or "SPM" (Surface Permanent Magnet) motors. Most likely the supplier you heard was meaning that THEY are finally getting on board.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[cswilson]

Conventional wisdom says you can't use permanent magnets in a self-starting AC synchronous motor as the synchronous torque-generating mechanism -- it must be a reluctance or hysteresis mechanism instead, because the PMs would cause too much back-and-forth torque when starting up.

By pete's description, it doesn't sound like they have gotten rid of this problem, but they seem implicitly to be claiming they have gotten it under control enough to have a usable motor. We'll see...

jraef: I can't find any IPM or SPM motors that are self-starting -- that is, when the line frequency is applied directly to the stator of a stopped motor, they could generate the torque to accelerate up to synchronous speed. Do you have any specific models in mind?

Curt Wilson
Omron Delta Tau

 

[jpts]

Normal PM machines (whether SPM or IPM type) are typically not able to start directly on-line as mentioned also by cswilson, since there is not enough reluctance torque or special starter winding (squirrel-cage) in the rotor. On the other hand, there is often no need to DOL start, since they are often operated with VFD that can do the starting smoothly.

It is quite well-known technology to add damper-/starter winding in the rotor of a PM synchronous machine, in case the machine needs to start directly on-line. It also helps in keeping the machine synchronized due to load disturbances (acts as a damper winding). However, it seems that these kind of machines are not so much commercially available. Maybe it is because variable speed drives can utilize normal PM machine without cage-winding (or standard induction motor without magnets), and in DOL applications running at constant speed, standard induction is much cheaper option. Only if very high efficiencies are required, then this kind of motor might be practical.