Electromagnetic force in electric motor

AI Thread Summary
In a DC motor with a permanent magnet and groove rotor, the electromagnetic force is calculated using the formula dF=jxBdv, where j is the electric current density and B is the magnetic flux density. The discussion highlights that while current density exists in the groove, the magnetic field is absent, leading to a zero force calculation. It is noted that the magnetic reluctance of materials like copper and insulation is significantly higher than that of steel, causing the magnetic flux to bypass the groove. The conversation also emphasizes that steel is not used for the armature due to its magnetic properties. Overall, the interaction between magnetic fields and current density in the motor's design is crucial for understanding its operation.
batsan
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Suppose we have a DC motor with permanent magnet. Moreover, the armature of motor is groove rotor. The elementary electromagnetic force is given by: dF=jxBdv, where j is electric current density , x is vector multiplication , B - magnetic flux density , dv - elementary volume. If we integrate by all the volume, we will calculate only zero, because there is current density j in the groove , but there is no magnetic field B. Otherwise ,there is B in the steel , but no j.
How you can explain that?
 
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There is B in the groove.
 
Are you sure?
The magnetic resistance of the groove materials, such as copper, insulation ,air etc is many times more then steel. The magnetic flux pass around the groove, but not inside it.
 
batsan said:
Are you sure?
The magnetic resistance of the groove materials, such as copper, insulation ,air etc is many times more then steel. The magnetic flux pass around the groove, but not inside it.
The hig magnetic reluctance (not resistance) of those materials is what permits the B field to enter the groove. That is why steel is not used for the armature.
 
Ok. Is this correct picture or not?
http://www.mfly.de/animation_b.gif
 
Last edited by a moderator:
The picture is colorful, but I don't think it is relevant to your question or my answer.
 
Yes,this is AC motor, but formula for its force must be the same. As we see color of groove is blue and it corresponds to B=0.
 
The picture is colorful, but I don't think it is relevant to your question or my answer, since B is not zero in the groove however they color it.
 

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