Re: 3 phase power converters
On Saturday 03 August 2019 23:30:47 John Hasler wrote:
> A static converter doesn't produce three phase. It converts a
> three-phase motor into a capacitor start, capacitor run single phase
> motor by connecting two of the phases to the single phase lines and
> connecting the third phase to one of the lines through capacitors. It
> only works for motors and needs to be tuned for a specific motor.
>
> A real motor generator set *will* produce 60 Hz three phase because
> the motor and generator will be synchronous. The power will also be
> seperately derived (not connected in any way to the single phase).
>
> More comon than real motor-generator sets are "rotary converters".
> These are large three phase motors wired up like the static converter
> discussed above but with slightly different capacitor values and not
> connected to any mechanical load. Three phase loads are then
> connected to the phases of the motor. This produces a fair
> approximation of three phase but note that two of the phases are
> connected to the single phase lines. This means that you have neither
> a neutral nor a grounded conductor (unless you are in Europe in which
> case you have
> corner-grounded delta).
Three phase, at most any frequency can be had a lot cheaper at up to 10
horse or so by using a suitably sized VFD. I'm useing 2 1.5 horse rated,
to drive a 1 horse 3 phase motor, currently available from ebay for
about a hundred bucks. Top frequency is 400 hz, but motor inductance
reduces the drive currant to under an amp a phase at around 200 hz, so
theres little torque to do work above 150 hz. But I can get turn the
house around torque at 5 hz, not forever because the motors fan does
not move cooling air when its not running at normal speed. But for a 20
minute job its fine. Lathe itself has an 8 speed drive, rarely changed
out of 5th, the vfd does it all.
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)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>
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