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how to increase RPM of 3 phase induction motor, through winding scheme change

how to increase RPM of 3 phase induction motor, through winding scheme change

how to increase RPM of 3 phase induction motor, through winding scheme change

(OP)
Hi.

I am trying to re-wind a 3 phase, 400Hz, induction motor. Despite multiple prototype windings, I am unable to achieve the desired RPM of 22000.

Here's the motor's official data.
(Pic attached)
Input power=650watts
Line current=2.1 Amp
Input voltage=200 Vac - 400Hz - 3 phase
RPM = 22500
Rotor (squirrel cage)=19 slots
Stator=18 slots


Stator Winding scheme used by me:

(see pic)
2-pole, 3-phase, Wire guage = 23
Each phase has 6 coils (35 turns each).
phase-A (pole 1) winding slots= 1-7, 2-8, 3-9.
Phase-A (pole 2) winding= 10-16, 11-17, 12-18.
phase-B (pole 1) winding= 4-10, 5-11, 6-12.
Phase-B (pole 2) winding= 13-1, 14-2, 15-3.
phase-C (pole 1) winding= 7-13, 8-14, 9-15.
Phase-C (pole 2) winding= 16-4, 17-5, 18-6.


Results:
Starting current=4 Amps
Steady current = 1.8 Amps
RPM achieved = 11900.
RPM desired = 22000


Can someone pl suggests how to increase RPM by improving upon the winding scheme? All other factors are fixed, since this is a repair job.

Regards.
FH

RE: how to increase RPM of 3 phase induction motor, through winding scheme change

no-load RPM for an AC induction motor is calculated by (Hz * 60 * 2) / (poles)

since 400 * 60 * 2 = 48000 = (4 * 11900) w/ 1% slip it indicates that you seem to have actually wired the motor as 4-pole, not 2-pole.

RE: how to increase RPM of 3 phase induction motor, through winding scheme change

Assuming you wound all the coils in the same direction, connect the end of phase A pole 1 group to the end of phase A pole 2 group. Repeat for other two phases. Are you sure that wire is 23 SWG?

Muthu
www.edison.co.in

RE: how to increase RPM of 3 phase induction motor, through winding scheme change

(OP)
@ JezNZ .
Thanks for your reply.
I definitely tried to make 2-pole scheme but there could be an error. Can you take a look at the wiring scheme I attached (as pic with original post) and advise how to turn it into 2-pole? (if you find my scheme as 4-pole).
Regards.

RE: how to increase RPM of 3 phase induction motor, through winding scheme change

(OP)
@ Edison123

"Assuming you wound all the coils in the same direction, connect the end of phase A pole 1 group to the end of phase A pole 2 group. Repeat for other two phases. Are you sure that wire is 23 SWG?"

Yes, this is indeed the way it has been wound Phase A (both poles in series)... and likewise for other two poles. Previously I used 27 wire but RPM was around 10,000. With 23 wire, it has increased to approx 11000 (both without load). The stated RPM of motor is 23000 and this is the shortcoming in repair so far.

RE: how to increase RPM of 3 phase induction motor, through winding scheme change

There are two ways you can connect pole groups in series.

A. Connect end of pole group 1 to end of pole group 2 = 2 poles

B. Connect end of pole group 1 to start of pole group 2 = 4 poles

You have obviously connected in method B and hence the half speed.

Changing the wire size (or turns) does not change the RPM. Only frequency and how you connect pole groups determine the RPM.

Muthu
www.edison.co.in

RE: how to increase RPM of 3 phase induction motor, through winding scheme change

You have 6 pole phase groups.

Assuming like edision did that all coils are wound in the same direction...

The typical 2-pole connection alternates electrical connection polarity of physically adjacent groups so that you end up with A B' C A' B C' which creates 60 electrical degrees separation in time between physically adjacent groups.

To make it go at 4- pole speed, I'm guessing you'd have to connect all coils in same polarity so you end up with A B C A B C which forces 120 electrical degrees between each group (maybe it's called consequent pole).

If you are beginning wtih a 4 pole speed (A B C A B C), then you need to flip electrical polarities of a single A, a single B and a single C in order to get to (A B' C A' B C') which would be 2-pole configuration.

=====================================
(2B)+(2B)' ?

RE: how to increase RPM of 3 phase induction motor, through winding scheme change

Consequent pole is an arrangement where the windings are the same magnetic polarity.
As a Consequence, the opposite poles are formed between the winding coils.
A Dahlander connection is a consequent pole connection.
A consequent pole connection halves the motor speed.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: how to increase RPM of 3 phase induction motor, through winding scheme change

(OP)
@JezNZ
@edison123
@electricpete
@waross

Thanks guys. Your inputs have been v helpful. I was mistakenly winding it as 4-pole per phase, Because of not flipping the connection of adjacent pole group / opposite poles. So the config was ABCABC.
Right now I am trying the correct scheme (AB’CA’BC’) and will be back with feedback / further questions :)

FH

RE: how to increase RPM of 3 phase induction motor, through winding scheme change

(OP)
@JezNZ
@edison123
@electricpete
@waross

Great results 👌. Now, after reversing polarity of opposite poles, rpm =23000 approx.
Thanks again n stay blessed.
Regards.
FH

RE: how to increase RPM of 3 phase induction motor, through winding scheme change

Now that you have done your experimentation, I hope you retained the original winding design in tact since this being a 400 Hz motor, I assume it's aircraft related where reliability, reliability and reliability are the three main mantras.

Muthu
www.edison.co.in

RE: how to increase RPM of 3 phase induction motor, through winding scheme change

(OP)
@edison123

Yes, Reliability is important and I have retained the original winding scheme (and wire gauge) indeed. smile
thanks n regard

FH

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