Re: VFD drive problems with older 3-phase motors (corre...

Ok, I thought I understood how these wirings were different, but it
sounds like I don't.

I measured the resistance between all permutations of the wires,
generating a table. From this and a little logic, I figured out which
wires were separated from others by one winding (~0.8 ohms). This gave
me all 'adjacent' wires. Then adding in the other measurements, I came
up with a complete diagram.

Now, my understanding of wye connections is that it has a common
connection in the middle and the windings radiate out from that
whereas the delta configuration have each winding only connected to
one other on each side, forming a loop, or a triangle shaped
configuration. I can see how an ohmmeter could make the same
measurements for either configuration as in the wye configuration
you'd just be measuring across pairs of windings.

With the dual windings, each leg of the triangle is composed of a pair
of windings. Taking every other connection (i.e. 1-2-3 or 4-5-6) you
get, I thought, a standard dual speed delta configuration.

As for phasing, I thought with three wires you can't get phasing
wrong. 1-2-3 will drive the motor one way. 1-3-2 will drive it the
other direction. There's no other possible arrangements that I can get
out of this that aren't identical.
1-2-3 = 2-3-1 = 3-1-2
1-3-2 = 3-2-1 = 2-1-3

If you charge the coils in the following order
1-2 phase 1
2-3 phase 2
3-1 phase 3
you drive the motor in one direction.
If you get the phases out of order:
1-2 phase 1
3-1 phase 2
2-3 phase 3
you drive the motor in the other direction

So what am I missing? Or do I totally misunderstand how the three
phase motors are wound/operate?

Thanks for the insights...
-Ted

--- In CAD_CAM_EDM_DRO@yahoogroups.com, cnc002@a... wrote:
> In a message dated 12/25/2003 5:52:03 PM Eastern Standard Time,
> pete@v... writes:
> Ted, how was the motor originally connected to the contactors? How
> could you possibly determine wye/delta from ohm-meter measurements
> when wye and delta circuits are electrically equivalent?
> Actually, the resistance measurements for wye connection would be
approx.
> double that of a delta connection within the motor. If the motor's
internal
> connection, or winding connection via and external terminal block,
etc., is a
> delta delta which is two delta configurations in parallel then the
single wye
> would be 4 times that of the delta delta.
>
> Now, to figure out the correct "phasing" connections of the internal
windings
> is a bit more complicated and requires the use of a voltmeter and a
6 or 12
> volt battery.
>
> Randy Abernathy
>
>
> [Non-text portions of this message have been removed]