S.E.R. Drives

[Freshsurfer]

Hi,

I´m trying to find some theory information about S.E.R. (slip energy recovery) drives, basically how this kind of drive can drive a motor above of the synchronous speed, if somebody can tell me where I can get this information or know well this kind of drive I will be grateful

 

[jraef]

Hello Freshsurfer,
AFAIK, a Slip Recovery drive works only with Wound Rotor Induction Motors, and uses the energy coming off of the rotor as a power feedback to the source. I'm not sure that it drives the motor supersynchronous though. Flowmatcher is one of the few companies that still make them.

http://www.flomatch.com/

partly due to the fact that WRIM's are falling out of popularity. Flowmatcher took over the engineering and product support of the originators of that technology, Marathon Electric (not related to the motor mfgr or terminal block mfgr). There is a brief description of the technology on thier website.

"Venditori de oleum-vipera non vigere excordis populi"

 

[Skogsgurra]

It is possible to run supersynchronous if you feed the rotor from a frequency inverter. I have seen a simulation somewhere (cannot find it now) where the rotor frequency was varied from full slip frequency (at standstill) to zero Hz for synchronous speed and then increased again (with 180 degree phase shift) for speeds above synchronous.

To be of any practical use, I guess that the drive has to be started with a starting resistor and run from a certain (say 70 percent) speed with the frequency inverter connected. It would then give a 70 - 130 percent speed range.

There has been some work done with asynchronous motors with a twin stator winding where the first winding is connected to the grid and the second winding is connected to a frequency inverter. The two stator windings are separately wound (side by side, no coupling in the stator between them)and the idea is that the second winding induces a frequency into the rotor cage (same thinking as when using a wound rotor and slip rings) so that the speed can be controlled by varying the frequency. The positive effects are that the frequency inverter needs only deliver the "difference power" and perhaps also that the mains harmonics are less than when running all power through the inverter. And, of course, no slip rings and brushes to maintain.

 

[mc5w]

Skogsgurra,

I have seen the U.S. patent for this motor by a Japanese inventor.

In one scheme the stator has a 4 pole primary winding and a 6 pole tertiary winding. The secondary winding on the rotor has 5 bars. Another way to do it is to have 4 pole and 8 pole windings on the stator and 6 bars in the rotor.

The tertiary winding on the stator is the one that connects to the external resistors.

Slip recovery drives are used nowdays only in wind tunnels because at supersynchronous speeds the horsepower rating of the motor is effectively doubled which you do need for say a 600 mile oper hour wind tunnel.

Mike Cole, mc5w@earthlink.net

 

[Freshsurfer]

Thanks Skogsgurra, I was talking with the people of IES that supply this kind of drives, this drive works as you said, while you can drive the motor up to the synchronous speed you always going to have a constant torque, this is the main condition to the system while the torque depends of the relation between power and speed, and when the inverter increase the frequency with 180 degree phase shift it injects energy to the rotor increasing the mechanical power due this the speed must to go up to maintain the torque constant, I´m trying to figure out how the inverter can shift the current phase, but my principal doubt is how about the formula that says that the speed is equal to 120*f/(# poles). I believe that exists an explanation to this