I think it is possible to "over-drive" an AC induction motor, that is why commercial drives can be configured for an acceptable slip between electrical motor frequency and actual mechanical speed of the rotor. The higher the voltage on the AC motor, the higher the torque and the lower the slip, but also the higher the current in the rotor. Unnecessarily high current just wastes power and heats up the motor, without significant reducing the slip, so you can lower the motor voltage to the point where the rotor slip is just acceptable for the torque you are demanding from the motor. If you need higher torque or speed, then you will need to increase the voltage on the motor but in steady-state / low torque operation there is no need for full AC voltage so commercial drives can modulate their output to lower voltage based on acceptable slip / torque demand. It is also needed to increase the max RPM that the drive can run the motor, for a certain supply voltage
The effect is similar to the "filed weakening" in DC motors. You see the SepEx motors also having an algorithm of how to apply enough field to deliver the work without constantly burning up the field coil. Hope this clarifies, Cor van de Water Chief Scientist Proxim Wireless office +1 408 383 7626 Skype: cor_van_de_water XoIP +31 87 784 1130 private: cvandewater.info http://www.proxim.com This email message (including any attachments) contains confidential and proprietary information of Proxim Wireless Corporation. If you received this message in error, please delete it and notify the sender. Any unauthorized use, disclosure, distribution, or copying of any part of this message is prohibited. -----Original Message----- From: EV [mailto:[email protected]] On Behalf Of Lee Hart via EV Sent: Monday, February 13, 2017 10:32 AM To: Marco Gaxiola; Electric Vehicle Discussion List Subject: Re: [EVDL] AC induction motor, rotor heating up.. Marco Gaxiola via EV wrote: > I have a question: Is that possible to have an AC induction motor to work > apparently normal but, after a moderate use, get the rotor coils very hot? > Not the stator neither the controller, just the rotor. Yes. The rotor is in effect the secondary of a transformer. This secondary is *shorted*, which leads to the high current, and heating. But the current produces a magnetic field. The stator coils create a rotating magnetic field that drags the rotor field along with it to make the motor work. The rotor windings are usually low resistance, to minimize losses and heating. However, it is pretty common to wind (cast) the rotor windings in aluminum, which has higher resistance and more heat. High rotor resistance also makes the motor easier to start, so it's sometimes done deliberately. -- Fools ignore complexity. Pragmatists suffer it. Geniuses remove it. -- Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
