Operating principle of a Six Phase induction motor

[makkena]

Hi Sir,
I have seen in many IEEE magazines that, a six phase induction motor is having two 3 phase windings spatially separated by an angle of 30 degrees electrical. I have attached the 6 phase induction motor diagram. But I am not able to understand how the motor operates i.e. how the rotor rotates when the 6 phase input supply is given.

Please provide me the answer. Thank you.

 

[SirAskalot]

Are you familiar with how the 3-phase motor creates a rotating field?

Where a pulsating wave is composed into a forward and backwards traveling wave? And how the sum of these waves creates a forward rotating wave?

Draw a vector diagram for the coil layout, take one instance of time and draw the field vectors (forward and backward wave) created by each coil /phase. Then do the vector addition to see the resulting wave.

 

[makkena]

Thanks for the reply sir.

Yes sir, I am familiar with how the rotating magnetic filed is produced in 3 phase induction motor.
It creates a rotating filed of constant magnitude 1.5 times the maximum value of flux and rotates at synchronous speed.

But in case of 6 phase induction machine, two three phase windings are there, which are separated by 30 degrees electrical. When a six phase supply is given to this machine, I am confused. I am thinking since two three phase windings are there, will there be two rotating magnetic fields ?

So actually I am not able to understand the principle of operation how the rotor rotates. So please explain me if you know the operation of six phase induction machine.

Thank you.

 

[SirAskalot]

Try using the same approach as with the 3-phase machine. The approach should still be valid.
Doing the math may be simpler than trying to think about how it works. Also note that in a 6 phase system each phase is separated by, not 120 degrees, but ?

Draw a diagram with the axis of each phase coil (6 coils for a simple motor). Write out the expression for each phase current ( 6 phases). Take one instance of time and note the amplitude of each phase current. Draw the flux vectors set up by each coil (in the diagram). Do the vector addition.

Try it, and report back.

 

[Averagesupernova]

Makkena, I am not sure you fully grasp what 6 phases are. Really nothing more than taking 3 phases and running each phase through a transformer to get a 180 degree phase shift from the original. Now you have a total of 6 voltages which none of them are in phase with each other. Now of course you can accomplish the same thing by simply reversing the way the poles are connected in a motor with 6 poles. Some specialty motors have many poles in them and run on plain old 3 phase power. There can be enough poles to get the motor speed down to several hundred RPM as opposed to the max of 3600 (synchronous)

 

[sophiecentaur]

Makkena, I am not sure you fully grasp what 6 phases are. Really nothing more than taking 3 phases and running each phase through a transformer to get a 180 degree phase shift from the original. Now you have a total of 6 voltages which none of them are in phase with each other. Now of course you can accomplish the same thing by simply reversing the way the poles are connected in a motor with 6 poles. Some specialty motors have many poles in them and run on plain old 3 phase power. There can be enough poles to get the motor speed down to several hundred RPM as opposed to the max of 3600 (synchronous)

That's just one method of implementing six phases. You could just as easily produce an alternator with six windings rather than just three. (They are not available off the shelf, though!)
One big advantage of a six phase motor is that there is less inherent vibration (as in a V 12 IC engine)

 

[Averagesupernova]

That's true sophie. I was just trying to simplify it down as much as possible.

 

[sophiecentaur]

The basic answer to the OP is to say that a three phase motor uses three coils, with physical angles pf 120 degrees between them and with phase angles of 120 degrees. A six phase motor has six coils with both physical angles and phases of 60 degrees. The principle of operation is exactly the same in both cases - a rotating magnetic field, which is chased by a passive armature.
You don't even need three 'proper' phases for an induction motor. A two phase (single phase supply) motor will operate but needs to be started by spinning the armature and is, on the whole, not a very good idea. Using a shaded pole, you can get enough phase difference between the phases of a magnetic field to produce some field rotation with just a single phase supply and such a motor doesn't need to be helped to start.

 

[Sutida Kerdsuwan]

Hi sir,

Could you please explain about Clarke’s decoupling transformations matrix for asymmetrical 6 phase machine or relation about each of subspace?

Thank you