- #1
smruti
- 20
- 0
synchronous machine can run at synchronous speed but why can't induction machine run at synchronous speed?
Synchronous Machines: Why Can't Induction Machines Run at Synchronous Speed?
- Thread starter smruti
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- Machine Synchronous
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Discussion Overview
The discussion centers around the operational differences between synchronous and induction machines, specifically addressing why induction machines cannot run at synchronous speed. The scope includes theoretical explanations and technical reasoning related to motor operation and electromagnetic principles.
Discussion Character
- Technical explanation
- Conceptual clarification
- Debate/contested
Main Points Raised
- Some participants explain that synchronous machines can operate at synchronous speed, while induction machines cannot due to the nature of their rotor design and operation.
- It is noted that induction motors rely on slip, which is the difference between the synchronous speed and the rotor speed, to induce current in the rotor's squirrel cage, generating torque.
- One participant describes the relationship between force, current, and magnetic fields, emphasizing that without slip, no current is induced in the rotor, resulting in no torque.
- Another participant mentions that as the load on an induction motor increases, the required force also increases, leading to an increase in slip.
Areas of Agreement / Disagreement
Participants generally agree on the fundamental principles governing synchronous and induction machines, but there are nuances in the explanations and implications of slip and torque generation that remain contested.
Contextual Notes
Some assumptions regarding the definitions of synchronous speed and slip, as well as the conditions under which torque is generated, are not fully explored, leaving room for further discussion.
- #2
Hesch
Gold Member
- 921
- 152
smruti said:
Asynchronous motors contain a rotor with a squirrel cage. When the cage has a different rotational speed than the speed of magnet field from the stator, an emf will be induced in cage, which results in a current. This current magnetizes the rotor, and a torque arises.
The difference in speeds is called the slip, which by synchronous speed = 0. No slip → no emf → no current → no magnetic field in rotor → no torque.
Synchronous motors can only run at synchronous speed.
- #3
Babadag
- 614
- 162
The force exercised on a wire through which a current flows in a magnetic field it is F=K*I*B- B=magnetic flux density [induction].Based on Newton second law the action [force]=reaction[force] that means this force acts on both-stator and rotor and rotor rotates.
In a synchronous machine we have a magnetic field in the rotor.
In asynchronous machine we haven’t. In order to create a magnetic field we need current. If the rotor run with the same velocity as the magnetic field produced by stator –as Hesch explained it very well-no current will appear in the rotor winding-squirrel cage or wounded rotor or else- that means no force will act on the rotor.
The speed difference-the slip=[synchronous speed-rotor speed]/synchronous speed-will produce a current at a low frequency =slip*supply frequency. Higher slip higher force.
As the load is increasing the required force increases and then the slip increases.
In a synchronous machine we have a magnetic field in the rotor.
In asynchronous machine we haven’t. In order to create a magnetic field we need current. If the rotor run with the same velocity as the magnetic field produced by stator –as Hesch explained it very well-no current will appear in the rotor winding-squirrel cage or wounded rotor or else- that means no force will act on the rotor.
The speed difference-the slip=[synchronous speed-rotor speed]/synchronous speed-will produce a current at a low frequency =slip*supply frequency. Higher slip higher force.
As the load is increasing the required force increases and then the slip increases.
- #4
Hesch
Gold Member
- 921
- 152
Babadag said:
Well, yes, with some limitations. Typical torque characteristic for an asynchronous motor:
- #5
Babadag
- 614
- 162
Thank you, Hesch.I agree with you of course.