Re: Switched Two or Three Speed Three Phase Motor

Richard wrote:
On Sat, 12 Apr 2008 13:09:23 +0100, Robert Wilson
<robwilson@xxxxxxxxxxxxxxxxxxxxxx> wrote:

Richard wrote:
<snip>

Cheers Richard
Sounds to me like is wired with different numbers of poles, which dictate that the speeds are roughly multiples of each other.

Rob.

Yes indeed Rob, you're quite right. There are physically 36 poles and
it's configured to run as a 2, 4 or 6 pole motor at high, medium or
low RPM. The switch has zillions of terminals and interconnections to
to re-configure the windings to run at the different speeds.

I have two concerns with trying to use my VFD:

Firstly potential damage to the motor during extraction of the
inteconnection tappings.

Secondly, the middle speed is delta connected to 415V. Each winding is
two windings in series which are switched into parallel with the line
to the centre tap and both ends being the star points to become the
star-star for high speed. Assuming I can get the interconnections out, I could connect the YY as
DD and run it from the VFD for high speed, but I can't quite get my
head round whether I could do the same for the mid speed having
swapped the polarity of one winding of each pair(phase).

I think I probably can, but high power electrical machines was only a
one unit course nearly 30 years ago......

Richard
Hi,
If it is a fairly intelligent drive then you should be able to put into the drive the number of poles via a menu parameter.

What suppy are you running the drive from? Not sure I can really comment with any confdence without seeing a diagram.

Most people are trying to run the drive from a asingle phase supply with a VFD, but then wonder why things are unpredictable when you try and run a 415 volt motor from it. You know you can turn a 400v machine into a 200v one by re-wiring the motor for delta. Don't forget the current will go up, but the torque will stay the same, just the speed will reduce.

Is that of any help or am I waffling?

Rob.
.

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