3ph motor winding 2

[retailer]

I have a milling machine that has the gearbox and motor share the same casting, it was originally 415v 3ph 50hz 2 speed, this coupled with a 4 speed gearbox gave 8 speeds. At the time as I only had a single phase supply and also as VFD'd were out of my reach pricewise I had a local winder rewind for single phase. It was not 100% successful, low speed lacked any power and was unuseable, however I managed with only the 4 speeds. Now that VFD's are very affordable I would like to rewind the motor back to 3ph 240v and use the VFD get that second speed.

I have lost contact with the original motor winder but have the following info from a different forum posted by a member that has an identical machine and has had his rewound to operate on 240v

Original nameplate specs:
3 phase 50Hz 415V speeds: 2810/1390 Amp:1.6/1.3 kW:0.66/0.48
'Dahlander', 'pole changing' or 'consequent pole' motor
General winding detail:
Slots 24
Coils 12
Pitch 1-6-8
Coil arrangement D, Y-Y (delta, double star)
Original coils for 3 phase 415V: 213 turns of 0.5mm diameter wire.
New coils for 3 phase 240V: 123 turns of 0.67mm diameter wire.

As the motor will be running from a VFD I feel I don't need the 2 speed option so a straight 4 pole delta connection is all that is needed for a speed of around 1400rpm. I have contacted local rewind shops and they are quoting figures around the $700 mark which is out of my budget but I often wind Tube output transformers and have the wire, insulation, varnish etc and feel it is with in my capabilities.

After reading up about 3ph motors on the internet I have drawn up a proposed winding layout and need to know if it is correct, I need it work first time as I don't want to risk damaging a new VFD. I have posted two images, one shows all the windings and interconnect between them and how they are placed in the stator slots, the other pic shows only one phase for clarity and the interconnects between the windings , the same interconnects between the windings is copied for the other two phases. Essentially each phase has 2 groups of 2 coils each in series I am expecting this to be 4 poles 240v 3 ph with a speed of approx 1400rpm. Will this work ?

Pics are here:-

http://s20.postimg.org/mhqbnokst/my_ph_motor_winding.jpg

http://s20.postimg.org/s76k7zqz1/my_ph_motor_winding_single_ph_shown.jpg

 

[rhatcher]

Retailer,

Your connection is incorrect. If you check, you will see that the delta connection creates two poles because the pole groups have opposite polarity and the two-wye connection creates four (consequent) poles because the pole groups have the same polarity. This is a constant horsepower connection.

For a constant torque connection, you need to reverse the start and finish of one pole group for each phase. This will cause the delta connection to have four (consequent) poles and the two-wye connection to have two poles. If you make this change and you still have the original two-speed motor controls then you can reconnect everything and operate the mill as a two-speed machine without the VFD.

Motorwinder's post of 29 May 23:43 shows a simple (and correct) two-wye, two pole connection. You can use this connection for VFD operation. As mentioned in an earlier post, the "Y" can be internally connected; there is no need to attach leads and make an external "Y" connection when operated on a VFD.

 

[petronila]

Hello Retailer

Only point you something, we know is a dahlander constant horsepower connection (In an european motor horsepower variance with speed so 1.6 kW is not equal to 1.3 kW), then High speed connection is Delta and Low speed connection is two wyes.

Taking account earlier calculations: " Original coils for 3 phase 415V: 213 turns of 0.5mm diameter wire.New coils for 3 phase 240V: 123 turns of 0.67mm diameter wire"

calculations were made with simple formulations: T2= T1 * V2/V1 T2= 213*240/415=123 Turns and for new wire diameter, new mm2 = old mm2 * T1/T2 = 0.65 mm diámeter.

For this new winding the conmnections can´t be changed, so the motor could be rewinded with this new turns and new wire size but connections most remains the same, due to the pitch, groups and coils per group not change you will have to connect again the motor like dahlander (six leads) and made external connections to have one speed or other.

If you want a single speed motor for 240 V, the best option is calculate winding taking account core sizes like Internal Diameter, Lenght, Back-Iron, etc.

Regards


Carlos

 

[retailer]

Thank you motorwinder for the double Wye connection and thank you rhatcher for the explanation and for guiding me in the right direction, it is much appreciated. I already have an almost full 10kg spool of .67mm wire and would prefer to go this way, from experience with transformers, bifilar winding is messy compared to a single wire coil. As you state there is really no need to have anything other than the double Wye connection as the motor is always going to be operated with a 240v VFD .

Not long after posting the diagrams on 29th May I could see that I had the coils connected incorrectly as when I drew a plan view of the stator with the coils spaced at 60deg intevals and tried to assign either a north or south pole to them based on an arbitary system where a +ve cycle of AC current gives a north pole for current flowing from start to finish, it was obvious that I did not have 2 poles rotating around the stator, I'd like to think I would have worked it out however motorwinders connection saved me a lot of time.

I have included a diagram that shows my interpretation of the connections as supplied by motorwinder, the leads marked 1 2 and 3 are the 3ph connections and the leads marked Y are the central star point of the double Wye connection, my plan view of the stator is also shown along with north or south pole assignments at 60deg intevals, the poles rotate 1/2 turn for 180deg of the 3ph sinewave, this would put the speed at 50x60=3000rpm minus slip.

Carlos, the motor will be connected as a Dahlander but it will be permanently connected as a double Wye I prefer to not have the option of using the speed change switch on the machine as I believe that this may damage the VFD if the speed is changed when the VFD is running.

I thank all who replied for taking the time to reply and help out.

http://s20.postimg.org/d3rsjdc5p/Diagram_4a.jpg

 

[petronila]

Hello Retailer

Attached you will find a winding diagram, due to your choice is 2 Wyes Connection(4 poles) in the case you want only three leads then conect together (internal) 1-3-5-7-9-11 and power the motor by 1-2-3.

Regards

Carlos

 

[rhatcher]

Retailer,

Nice job with the drawing that you submitted on 3 June. This is the correct connection.

With the VFD you will have an increased, continuously variable, speed range when compared to the original two speed operation. This may allow you to "fine tune" your milling operations. However, keep in mind that the motor's constant torque speed range is from 3000-1500 rpm. For the VFD, this is 50-25 hz. If you operate below 25hz at full torque (full current) then the motor will overheat. That being said, with the proper selection of frequency and gears you should be able operate at any speed between the original full speed and low speed.

Good luck with the rewind and let us know if you have any more questions or comments.

PS: In most caaes you are better off selecting the lowest switching frequency that your VFD allows. This may result in a slight increase in motor heating due to increased harmonics and an increase in audible motor noise but this is theoretically offset by reducing the hazard of failure due to the magnitude of the VFD voltage switching spikes.

 

[lukin1977]

Retailer: can you give me the Arboga contact info? I need to get in touch with them too about an old wire drawing machine

Thanks

lukin1977

 

[retailer]

lukin

I believe this is their web page

http://www.arbogamachinery.com/startsida/

I emailed them using the email address in the contact info at the bottom of the page.