The stator magnetic field and rotor magnetic field rotate at the same speed i.e they are stationery with respect to each other.
Stators and rotors
- Thread starter Sahib
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<Sigh>
No. Technically not true either. Ever hear of slip speed? The stator fields will rotate at the line frequency synchronous speed, the rotor fields will rotate slightly slower because they must be induced by the stator fields first.
And before you venture off on another irrelevant tangent, in a synchronous motor there is no slip speed, the rotor turns at the synchronous speed, but the rotor field is DC so it isn't rotating, therefore that doesn't count either.
Iam sorry jraef, you are wrong. It is not the rotor field that should rotate slower. It is the ROTOR.
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Oh for crying out loud...
:slaphead:
Phil Corso
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jminer99er
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Where's the darn "eating popcorn smiley"
winnie
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My understanding matches Sahib's in this case.
The stator magnetic field speed is set by the applied frequency and the pole structure.
The rotor _mechanical_ speed is different from the stator _magnetic_ speed. The rotor has slip.
In a rotating frame of reference, synchronized to the rotor, the rotor conductors see a very slowly changing AC magnetic field. This AC magnetic field induces currents in the rotor, creating the rotor magnetic field.
The magnetic field induced in the rotor is itself a rotating field even in the rotor reference frame.
The magnetic field induced in the rotor is synchronized with the stator field.
-Jon
The stator magnetic field speed is set by the applied frequency and the pole structure.
The rotor _mechanical_ speed is different from the stator _magnetic_ speed. The rotor has slip.
In a rotating frame of reference, synchronized to the rotor, the rotor conductors see a very slowly changing AC magnetic field. This AC magnetic field induces currents in the rotor, creating the rotor magnetic field.
The magnetic field induced in the rotor is itself a rotating field even in the rotor reference frame.
The magnetic field induced in the rotor is synchronized with the stator field.
-Jon
What's new? But be careful. I got chastised a while ago buy one of he moderators via a PM for my comments about OPs. I have learned to not respond to those posts anymore not wasting my time and just sit back and watch others spinning in circles which I often refer to as shooting at shadows.
I thought I was the exception......
Actually the rotor field has a fixed speed with respect to rotating rotor equal to slip speed.
Julius Right
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- Electrical Engineer Power Station Physical Design Retired
I agree with Jraef, of course.
Let's say the rotating magnetic field is a ring of permanent magnet poles [N-S]. Let's say these poles do not rotate but only rotor is rotating with the difference of velocities. That means it rotates backward [counter clock wise] with the speed of v=slip*2*pi()*f/p*Rgap [Rgap=radius of the gap; p=number of pole pairs].
When a rotor bar of speed v passes a pole of B field an emf is produced E=B*leng of bar*v and since there are 2p poles [p pair of N-S] an emf wave will rotate with v velocity of the rotor.
A current will circulate through the bar but the current wave is delayed with the impedance angle and will produce a connected with rotor field wave.
This field wave rotates with the f*(1-s)*60/p rpm.
Since each rotor bar will pass the same pole at different time a different angle has to be applied for each current in each bar. You may consider then [if you want it] each bar as another phase [or not]. However, as you could see, no 3 phases are involved here but only number of poles. Of course, we give balanced 3 phase current (distributed in time) to balanced 3 phase winding (distributed in space) to produce the stator field.
Let's say the rotating magnetic field is a ring of permanent magnet poles [N-S]. Let's say these poles do not rotate but only rotor is rotating with the difference of velocities. That means it rotates backward [counter clock wise] with the speed of v=slip*2*pi()*f/p*Rgap [Rgap=radius of the gap; p=number of pole pairs].
When a rotor bar of speed v passes a pole of B field an emf is produced E=B*leng of bar*v and since there are 2p poles [p pair of N-S] an emf wave will rotate with v velocity of the rotor.
A current will circulate through the bar but the current wave is delayed with the impedance angle and will produce a connected with rotor field wave.
This field wave rotates with the f*(1-s)*60/p rpm.
Since each rotor bar will pass the same pole at different time a different angle has to be applied for each current in each bar. You may consider then [if you want it] each bar as another phase [or not]. However, as you could see, no 3 phases are involved here but only number of poles. Of course, we give balanced 3 phase current (distributed in time) to balanced 3 phase winding (distributed in space) to produce the stator field.
Would you care to provide a link?
not allowed
it's in the Fitzgerald Electric Machinery Text, 6th Edition
Ch 6 Polyphase Induction Machines
pages 308-309
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Yes, please don't feed the trolls.
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Then rotational speed N of rotor field with respect to rotor N=sxfs/P, where P= number of pole pairs same as stator's. But fs=ns*P. Substituting we get
N=ns-nr. Here ns-nr is rotational speed of rotor field with respect to rotor. But rotor itself rotates at a speed of nr. So rotational speed of rotor field with respect to motor frame is (ns-nr)+nr=ns same as that of stator field.
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Your cited article makes no case for thaat.
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