Re: 5HP rotory elect. phase control

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Steve White by way of Terry Fritz <twftesla-at-qwest-dot-net>" <slwhite-at-zeus.ia-dot-net>

Yes, a simplified model is what I had in mind much as what you are
suggesting. I do not want to get into secondary effects such as you mention.

Steve: Coiling in Iowa

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, March 29, 2002 9:52 AM
Subject: Re: 5HP rotory elect. phase control


> Original poster: "Dave Lewis by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<hvdave-at-earthlink-dot-net>
>
> Steve,
>
> Since the motor runs at constant RPM, a very simple model could be
> used.   An inductor in series with a resistor would do the trick.   The
> RL values can be obtained by measuring the amplitude and phase angle of
> the motor current with respect to the voltage.   I think this a
> measurement is necessary since there are so many factors to consider
> that it just easier to measure it.
>
> Once you have the current amplitude and phase angle you can calculate
> the RL model parameters.
>
>                     V * tan(a)
>       L = ---------------------------------------
>            2 * Pi * f * I * sqrt( 1 + tan(a)^2 )
>
>
>            2 * Pi * f * L
>       R = ----------------
>                tan(a)
>
> Where:
> L in Henerys
> V in Volts rms
> a is phase angle 0 to 90 deg or 0 to Pi/2 radians, take your pick
> Pi is 3.142
> f is 60 Hz
> I is current amplitude measured in Amp rms
> R in Ohms
>
> For a 120V, 60Hz, and 1 Arms current lagging at 30deg I got L=0.159 and
> R=104.
>
> Other models are plausible and just as valid since the frequency is
> always 60Hz.  It shouldn't matter which model you use as long as the
> impedance at 60Hz is correct.  For instance a parrallel RL would work
> too.
>
> This is a simple model and will not address other issues such as start
> up and loss of sync.  To do so would require a much more sophisticated
> model that includes the rotor impedance and slip frequency among other
> things.  These models typically require a host of measurements on the
> motor to construct and probably not worth it in the end.
>
> Regards
> Dave Lewis
>
>
>
>
> Tesla list wrote:
> >
> > Original poster: "Steve White by way of Terry Fritz
<twftesla-at-qwest-dot-net>"
> <slwhite-at-zeus.ia-dot-net>
> >
> > Does anyone know of an adequate model for a motor while running? An
> > inductor? I have been looking at John Freau's phase shifter circuit and
it
> > appears to be a bandpass filter with a center frequency of 60 Hz feeding
the
> > motor. If I could model the motor, I could analyze the filter
> > characteristics. I presume that as the inductor (variac) is varied, the
> > center frequency of this bandpass filter changes slightly. This would
> > explain why you want to see a resonant rise. The presence of the
resonant
> > rise would indicate that you have implemented a 60 Hz center frequency
> > bandpass filter. Since analog filters have a non-linear phase
> > characteristic, this would also explain why the phase shifting action
takes
> > place. As you change the inductance, you slighlty change the center
> > frequency of the filter and also changes the phase angle of the voltage.
If
> > I could model the motor, I think that I could analyze the filter
> > characteristics and quantify the component values. I am attempting to
remove
> > most of the guess-work from selecting the capacitance value for a
particular
> > motor.
> >
> > Steve: Coiling in Iowa
> >
> > ----- Original Message -----
> > From: "Tesla list" <tesla-at-pupman-dot-com>
> > To: <tesla-at-pupman-dot-com>
> > Sent: Wednesday, March 27, 2002 11:31 AM
> > Subject: Re: 5HP rotory elect. phase control
> >
> > > Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> > <FutureT-at-aol-dot-com>
> > >
> > > In a message dated 3/27/02 1:16:06 AM Eastern Standard Time,
> > tesla-at-pupman-dot-com
> > > writes:
> > >
> > >
> > > >
> > > > so this encouraged me to finish my 5HP 3600 RPM rotory project.
> > > > I was a little worried about being able to make John Freau's phase
> > > > control work on such a large motor, but it does work after all.  The
> > > > optimal capacitance is around 85 uF using a 10 amp 120 volt variac
for
> > > > control.
> > >
> > >
> > >
> > > Hi Kevin,
> > >
> > > Nice !   I think the 240 volt operation lets the cap value be much
> > > smaller than otherwise.  Perhaps 1/2 or 1/4 the size that it would
> > > need to be for 5HP at 120 volts.  Your results also strengthen my
> > > suspicion that the cap value requirements depend somewhat on
> > > the motor load, not only on the motor HP rating.
> > >
> > > Cheers,
> > > John
> > >
> > >
> > >
>
>
>
>