At 11:05 AM 3/1/02 -0600, you wrote

Hello John:-


>         Thanks for the reply. I was beginning to think that my question
> is too
>far out there.
>Our stuff is so specialized that changing the motor is not an option. The
>physical configuration of the motor, it's ability to run at 200 C, the power
>charateristics, are all quite specific to our application

Ah, <light buzzing, flickering, then turning on> a *down-hole* application.

>         The wire in question is a 7 conductor cable. Once again, quite
> specific
>to the purpose of well logging.

Kapton or teflon insulation.

>Using 4 conductors for the motor power, at about
>11 ohms/1000ft, we have about a 400 volt drop from surface to tool. We
>only need
>to control from about 85% to 100%, in order to maintain optimum power
>factor. The
>purpose is to keep the motor running in that part of the curve where we
>achieve
>optimum performance without generating heat with excessive voltage. The
>motor is
>optimum at 3450 RPM. By monitoring speed at the surface, we can
>auto-adjust the
>voltage/current going downhole.

Okay. So we have a motor with 16 km of loop cable running to it. Sounds
"interesting" in an engineering sense. ;-)  Potentially some transmission line
effects, the reflection time would be of the order of a typical PWM frequency.
Probably best to keep that stuff outa there, filter it at the surface. Not to
mention the effects on your logging.

>         So I guess that's probably more than you wanted to know, but I'm
> not good
>at short answers.

All good information. With the narrow range, maybe you can keep with the
capacitor
and just use a single synthesized sine wave supply at some loss in
efficiency, but
if you are making something maybe might as well go for the two-phase.
Sounds like
an interesting project. You could use a DSP or PIC to synthesize the
2-phase AC.
Or an analog oscillator.

Best regards,

>         John Marshall
>
>
> > In theory, this could be done by generating two variable-frequency 600VAC
> > RMS sine waves using PWM that are 90 degrees out of phase (eliminating the
> > capacitor). In practice, for a one-off serious application, this would
> > be pretty much insane to try and make. You want to buy a Variable Frequency
> > motor drive and probably replace the motor with a 3-phase motor. You may
> > well need to add some power conditioning stuff at the end of your 5 miles
> > of wire, so talk to an experienced supplier.
> >
> > Then your main issue will be communicating with the motor drive.
> >
> > Best regards,
> >
> > Spehro Pefhany --"it's the network..."            "The Journey is the
> reward"
> > speff@interlog.com             Info for manufacturers:
> http://www.trexon.com
> > Embedded software/hardware/analog  Info for
> designers:  http://www.speff.com
> > 9/11 United we Stand
> >
> > --
> > http://www.piclist.com#nomail Going offline? Don't AutoReply us!
> > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body