Motor theory.

Any motor experts here. I had a 3 phase motor blow up at work. Removed for rewind. It's a two speed delta wye wye motor. Wiring diagram looks like star delta configuration but clearly it is a set of wye connected windings with an internal star point, 1st speed and 2nd speed has external contactor star point that when energised disconnects power to the 1st speed windings but provides it through a 3rd contactor in star via external star contactor Can anyone explain the theory of this too me please as when next on shift I wont be able to take winding resistance readings as it will be in use. Does 1st speed have lower resistance than 2nd speed so 2nd gets stronger stronger flux etc.
Tia.

Are the high speed and low speed multiples of each other?

Nozzle

I'm thinking the winding is centre tapped for 1st speed and the 2nd speed brings in the full winding . Like I said, 1st time seen one.

Assumption : it doesn't have a slip-ring rotor
Speed of a 3-phase motor is based on number of poles and will run at slightly lower than sync speed.
2-pole sync is 3000RPM, 4-pole sync is 1500RPM and 8-pole sync is 750RPM
I suspect your 2-speed motor is wound such that the windings are reconfigured from 2-pole to 4-pole etc

edit: added the "-ring" in slip-ring. Normally used to produce a "soft" start

SO. Is it 2 starting speeds or 2 running speeds?
How many connexions total?

There are a number of ways of doing this, Jackrae speaks a lot of truth however it's not always done that way.

EDIT: I've read your OP again and from your description it seems it has 6 terminals and is most likely to be a Darlander wound motor.

It has 6 wires induction motor. It starts in 1st speed in what sounds as half speed of speed 2, so the 2 and 4 pole configuration seems to fit this theory. You can select the speed you want to run at depending on product but speed 1 is always 1st pulse on control selector joystick. Think l need to brush up on my motor theory for effects of flux,current, bemf etc.

JACKC said:

It has 6 wires induction motor. It starts in 1st speed in what sounds as half speed of speed 2, so the 2 and 4 pole configuration seems to fit this theory. You can select the speed you want to run at depending on product but speed 1 is always 1st pulse on control selector joystick. Think l need to brush up on my motor theory for effects of flux,current, bemf etc.

Click to expand...

A standard star-delta starter will appear to work as you describe.
The best clue is look at the wiring; u1& u2 will be on different phases for star-delta but usually [but don't have to] be on the same phase for a Darlander 2speed motor.

The Darlander in essence consits of 2 windings in series per phase with an internal star point [rarely but sometimes brought out onto a terminal marked 'K'] shown in black.
In low speed the 2 windings are powered in series,
In hi speed power is applied to the mid point of the pair and a second star point is created:

These are designed to run at 2 speeds and cost a little more due to having 6 windings [note these are definitely NOT 3 tapped windings], some describe High speed as running the windings in parallel as there are now 2 star points, however this is not facually correct, when I have able to measure between the 2 star points I've found significant voltage which varied with the mechanical load applied.

This describes a star-star [Y-Y] motor, a star-star-delta requires at least 9 terminals but is more likely to be 12.

EDIT: Closing down for Bed I suddenly notice I've been misspelling Dahlander.


Comparison showing similarity between Darlander and star-delta power connexions.