Current Linkages in a Motor

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In summary: But based on the context and equations provided, it seems to refer to the "magnetic flux" or "magnetomotive force (MMF)" in the salient pole motor. In summary, the author is discussing the current linkage, Θf, in a salient pole motor and its representation using Ampere's law. The current linkage is a constant value due to the uniform magnetic field created by the DC excitation current. The author simplifies the analysis by considering the iron as a short circuit for magnetic flux.
  • #1
BlackMelon
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Homework Statement


I have a doubt about the current linkage, Θf, in figure 2.2b of a salient pole motor. In this textbook, the current linkage is expressed by ∫H⋅dl = Θf = ∑i. However, in the figure 2.2b between q(left) and q(right), how can the Θf be constant? Since, the author doesn't show how he chose the Amperian loop, how can I know how many currents are enclosed (∑i)?

2. Homework Equations

∫H⋅dl = Θf = ∑i

The Attempt at a Solution


I have studied the application of Ampere's law to solenoids, which have the same type of winding as that on the rotor of a salient pole machine. I was trying to assume so many Amperian paths, trying to figure the 2.2b out.
 

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  • #2
I don't know if you solved this one or not, as I see you created this thread a while back.

If you look at page 3 in your attached pdf document the author writes:
The salient-pole windings located on the rotor or on the stator are mostly used for the DC magnetizing of a machine. The windings are then called magnetizing or sometimes excitation windings. With a direct current, they create a time-constant current linkage [itex]\theta[/itex].

So, look at my bad paint drawing below. Coils are wound around the salient pole, creating a magnetic field in the upward direction (thumb towards current direction (x inwards, dot outwards) and your hand curls in the direction of the magnetic field). And as I quoted from your pdf, the salient pole is excited using DC current, which means that the magnetic field created from the coils wound around the salient pole is constant. Therefore we have this approximately uniform magnetic field across the salient pole and hence ~uniform "current linkage" if we ignore the edge effects.Did I answer your question? I have been lurking a few months on this forum and based on my observations I believe @jim hardy would have an input on this if you need more help or I did not answer it properly.
salientpole.png
 
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  • #3
Hmmmm

what he calls "current linkage" is what i call MMF ?

@Baarken got it i believe

In his example 2.1 your author simplifies things for us by considering iron to be a short circuit for magnetic flux .
salientmmf.jpg


There can be no circumferential MMF along the iron. It'd cause infinite flux .
Actually no radial MMF in the iron either - it's all spent in the airgap.
 
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  • #4
jim hardy said:
what he calls "current linkage" is what i call MMF ?

That was what I assumed as well, I have not heard or used the term "current linkage" before.
 

1. What are the main components of a motor?

The main components of a motor are the stator, rotor, and commutator. The stator is the stationary part of the motor that contains the electromagnets. The rotor is the rotating part of the motor that contains the permanent magnets or electromagnets. The commutator is a device that helps to switch the direction of current flow in the motor.

2. How do the current linkages work in a motor?

The current linkages in a motor work by creating an electromagnetic field. When an electric current flows through the stator, it creates a magnetic field. This magnetic field then interacts with the permanent magnets or electromagnets on the rotor, causing it to rotate. The direction of current flow is switched by the commutator, which creates a continuous rotation of the rotor.

3. What is the purpose of the commutator in a motor?

The commutator in a motor serves two main purposes. Firstly, it helps to switch the direction of current flow in the motor, which is necessary to create a continuous rotation of the rotor. Secondly, it helps to keep the current flowing in the same direction through the electromagnets, ensuring a consistent magnetic field for efficient motor operation.

4. How does the speed of a motor relate to its current linkages?

The speed of a motor is directly related to its current linkages. The stronger the current flow, the stronger the magnetic field created, and the faster the motor will rotate. On the other hand, if the current flow is weak, the motor will rotate at a slower speed. Therefore, controlling the current linkages in a motor is crucial in regulating its speed.

5. What are some common applications of motors that use current linkages?

Motors that use current linkages are widely used in various applications, including electric vehicles, household appliances, industrial machinery, and robotics. They are also used in power tools, fans, pumps, and many other devices that require rotational motion. Essentially, any device that requires the conversion of electrical energy into mechanical energy can use a motor with current linkages.

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