On Sunday 14 June 2015 17:32:07 andy pugh wrote: > On 14 June 2015 at 17:14, Gene Heskett <[email protected]> wrote: > > So how do we discern the induction motor,totally unsuitable for vfd > > drive except near is design rpms, from the synchronous motor at home > > on a vfd drive? > > I think there is a false assumption here. VFDs are _intended_ for > driving induction motors. All my machines have squirrel-cage induction > motors driven by VFDs on the spindles. The Harrison still has the > original motor from 1970.
Humm, that does not grok with what I understand is the actual motive force that turns the induction motor armature. 1. The slip angle that causes the current in the armatiure is basically a velocity effect. Reduce the driving frequency from 60 hz to 6hz, and one or both of 2 things are going to happen. 1a: The currents, because the inductance is still the same, now have time to rise to destructive, fusing of the wire in the windings levels. This will likely saturate the iron at the same time. 1b: If the currents are controlled so that they remain the same, then the rate of change of the magnetic field is reduced to 10%, inducing only 10% of the currents in the squirrel caged armature, with resulting severe loss of torque. Not to 10%, but because the effects are additive, but closer to 1% of the torque it can deliver when drven at 60 HZ. That in either event does not seem to be a viable way to spin a 1/2-13 USS tap at say 300 rpms. 2. So, do I not understand what I have learned from 65 or 70 years ago, or has a new way to drive such an induction motor that cancels or defeats the low speed power/torque losses? Educate me please. Thanks. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
