On Friday, July 30, 2010 10:30:29 pm Jon Elson did opine: > Don Stanley wrote: > > On Thu, Jul 29, 2010 at 1:17 AM, Jon Elson <[email protected]> wrote: > > > that is a common-mode choke, > > > > I understand common-mode in cabling and assume the same principal but > > not sure of all this means. > > > > > and there the main motor currents all cancel out, > > > > This is a ?? for me. > > OK, if all three phase wires enter the core window in the same > direction, then any motor current is supposed to flow in one wire and > return through one or two of the others. Therefore, the net flux in the > core MUST be zero, as the sum of currents in all three wires has to be > zero.
While true, sort of, what that does do is a great job of blocking 'longitudinal' noise at the higher frequencies, making the shops background radio work again. :) > > so laminated cores should be fine. At the lower frequencies. I would still prefer one of Arnolds higher magnetics toroids for that myself. > > My question is, "in what circumstance would it not work", > > so I can avoid that in the future. The common 'E' frame stampings of grain oriented silicon steel are pretty good below half a kilohertz, but a properly chosen toroid will still be actively working at gigahertz frequencies. It will usually take less wire on the stamped steel stacks to get the inductance wanted. > Well, putting a laminated core on a single phase wire would subject it > to the full PWM frequency spectrum of the VFD, as the VFD puts out 340 V > square waves of varying pulse width at some high frequency of several > KHz. Core losses are roughly proportional to frequency. So, core > laminations that are fine at 60 Hz will heat up 100 times more at 6 > KHz! It will not be quite that bad as the higher frequency causes less > peak magnetization, but it will still be a dramatic increase. Yes. This is why all the switch mode power supplies on the planet use ferrite toroid or cast E frame Ferrite cores. The cast/molded E frame, with its matching cap bar, give the designer yet another variable to play with, because the air gap between the two parts can be adjusted with a taped on film to help prevent core saturation, something that must be guarded against else the circuit self destructs. > Jon -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The young lady had an unusual list, Linked in part to a structural weakness. She set no preconditions. ------------------------------------------------------------------------------ The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
