2-speed 3-phase motor

Hi

Before I go through the hassle of going to a motor specialist...

This is from an Emco lathe (photos attached). It's a 3-phase, 2-speed, 2pole/4pole motor. For some reason the plate says the speeds are 1300/2700... I'd expect it to be exactly half/double but maybe just an approximate spec(?).

Specs:
380V
0.52/0.81 kW
△/YY
1300/2700 1/min
2.85/2.1 A
50 Hz

First thing, I was told (at the Emco group) that on the Emco 2-speed motor, high speed is triangle (delta) connection and low speed is star connection. Looking at the plate now, it seems the opposite? I think the YY means double star and the triangle means delta? I assume it is written this way the same as all other specs (left side is specs for low speed, right side for high speed)?

Second thing, I operate the lathe with a VFD (1-phase input to 3-phase output), since the original switch board is missing and I don't have 3-phase mains right now (I actually do, but can't wire it there right now).
It was working with a very old VFD for a long time, it was defective so I replaced it (this fixed the main issues with the old one).

The previous owner said it is connected on the high speed. I'm measuring spindle speeds with the way it's connected right now and I get pretty close to the low speeds (just slightly more which I understand is normal).

According to the Emco group, the motor has six wires. For delta/triangle wiring, there are three wires going to the VFD and the other three wired together between themselves, but to nothing else. Star wiring would be the other three wires to the VFD (those that are wired to themselves in the delta wiring), and the other three wires isolated each separately, not wired to anything.

So the question is, am I right about the wiring being reversed i.e. triangle/delta for low speed and star (or double star) for high speed? The alternative is that I'm doing something wrong with the VFD, but it does say 50Hz output.

Thanks very much

Nitai

Appears as if it is like this. "Vitesse inferieure" would be low speed

http://www.practicalmachinist.com/v...spd-constanttorque-iec-connection-diagram.jpg

I'm a bit late adding my two pence to this question, but yes, you would be correct. This is not exactly the same coil layout but the theory is the same. Have drawn magnetic poles to give a better understanding of this type of winding. can view at Symptoms.

Burnt out and windings... - Electric Motor Repair | Facebook

Drawn YY in a delta arrangement instead of conventional three pairs in parallel star for clarity.

It sounds like a Dahlander winding. If so, you can keep it on the high speed connection and get the full range with the VFD. That will give you the same torque at half speed that it normally gives on the half speed setting. Recently I have set up several cylindrical grinder wheel and spindle motors that way to give the operator more flexibility. I used a potentiometer control and adjusted the readout on the VFD to read in RPM so the operator only has to turn it to the desired speed for the wheel diameter, etc. They can set a worn down wheel to the optimum surface speed by turning a knob.

There is a lot of information to be found by Googling "Dahlander motor".

Bill

" That will give you the same torque at half speed that it normally gives on the half speed setting."

Not exactly. Motors like this, run on VFDs, are constant torque below namplate speed, and constant hp above
nameplate speed.

Probably you were saying, it gives the same HP at half speed (via VFD) as you would get at the low speed
setting, run on utility three phase power. Which is true.

jim rozen said:

" That will give you the same torque at half speed that it normally gives on the half speed setting."

Not exactly. Motors like this, run on VFDs, are constant torque below namplate speed, and constant hp above
nameplate speed.

Probably you were saying, it gives the same HP at half speed (via VFD) as you would get at the low speed
setting, run on utility three phase power. Which is true.

Click to expand...

What I meant was that the torque would be the same if connected for high speed and run on the VFD at half speed as it would be if connected for half speed and run on the line. A Dahlander motor delivers the same torque in both modes. Consequently, there is no loss in performance in going to the VFD.

Bill

9100 said:

What I meant was that the torque would be the same if connected for high speed and run on the VFD at half speed as it would be if connected for half speed and run on the line. A Dahlander motor delivers the same torque in both modes. Consequently, there is no loss in performance in going to the VFD.

Bill

Click to expand...

Concur!

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