The discussion centers on the interaction between rotor and stator flux in a three-phase induction motor, emphasizing that both fluxes rotate at synchronous speed and appear stationary relative to each other under normal operating conditions. It is established that slip, defined as the difference between synchronous speed and rotor speed, is crucial for torque development. If the angular speeds of the rotor and stator flux were to differ, it would indicate a fault condition, leading to uneven torque and potential rotor vibrations. The physics of the motor prevents such a scenario under normal conditions.
PREREQUISITESElectrical engineers, motor design specialists, and students studying electric machines will benefit from this discussion, particularly those focused on the operational principles of three-phase induction motors and torque dynamics.
There isn't. They rotate at the same angular speed at any loading condition, hence they always appear stationary to each other.Noaha said:What will happen if there is relative speed between them?
I think that would require a pretty big post to explain. I believe you can find the explanation in any standard electrical engineering book. If you are still unclear, you can post some specific queries.Noaha said:How these two fluxes interact with each other to develop a torque?
cnh1995 said:There isn't. They rotate at the same angular speed at any loading condition, hence they always appear stationary to each other.
Slip is the *mechanical* speed difference between rotor & stator. As loading changes, slip also x hanged, but both magnetic fluxes revolve at synchronous speed for any load value.Dr.D said:Doesn't this indicate that there is no slip? If slip is zero, there is no torque developed in an induction machine. I think this is mistaken.
cabraham said:x hanged
cabraham said:Slip is the *mechanical* speed difference between rotor & stator.
?Dr.D said:but that is not correct the slip.
This is right. But what I want to know is how it will effect the machine if their angular speeds are not same? Like what will the effect on torque developed or efficiency.cnh1995 said:They rotate at the same angular speed at any loading condition
It never happens unless there is some fault in the motor, like when one or two of the stator phases get open circuited, or when there are broken rotor bars etc. That results in an uneven torque and rotor vibrations. There may be some other abnormal conditions that can cause unbalanced magnetic pull. But that is a whole different topic and is taken care of while designing the motor.Noaha said:But what I want to know is how it will effect the machine if their angular speeds are not same?
That was informative. Thank you.cnh1995 said:It never happens unless there is some fault in the motor, like when one or two of the stator phases get open circuited, or when there are broken rotor bars etc. That results in an uneven torque and rotor vibrations. There may be some other abnormal conditions that can cause unbalanced magnetic pull. But that is a whole different topic and is taken care of while designing the motor.
Under normal working conditions, the physics of the motor does not let it happen.
Noaha said:But what I want to know is how it will effect the machine if their angular speeds are not same?
Typo, sorry, should read "changed". Anyway, the revolving fields both have an angular speed equal to synchronous speed. For 4 poles at 60 Hz, that is 1800 rpm. Call this 100%. The rotor mechanical speed is a little less, around 98%, for example, which is 1764 rpm. The slip is 2%.Dr.D said:?
Even though this is basic, this is something new for me. With this I understood why the stator and rotor flux should have same speed. Thank you.jim hardy said:product of two sinewaves of different frequencies averages to zero
Are you talking about single phase induction motor here?jim hardy said:You see this on a washing machine motor when trying to start it with the wrong start winding energized.
It just hums(really loud) and gets hot.
That's because the start and run windings with their different #s of poles make their respective rotating fields at different frequencies , not same frequency with just differing phase that's necessary to produce a rotating field
Yes.Noaha said:Are you talking about single phase induction motor here?