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an investigation of dual stator winding induction machines

an investigation of dual stator winding induction machines

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theory itself is correct. The inaccuracy under rotor eccentricity conditions comes from<br />

some simplification or assumption during the equation derivation. Hence the name<br />

“extension <strong>of</strong> the <strong>winding</strong> function theory” may not be proper.<br />

The derivation <strong>of</strong> the general <strong>winding</strong> function from the fundamental relationships is<br />

the subject <strong>of</strong> this section. With all the assumptions or simplifications removed, a general<br />

equation for the <strong>winding</strong> function <strong>of</strong> a <strong>winding</strong> distribution c<strong>an</strong> be obtained.<br />

A general diagram <strong>of</strong> <strong>an</strong> electric machine is given in Figure 3.1, in which the air gap<br />

length may not be const<strong>an</strong>t. A closed area which includes the <strong>stator</strong> core, the air gap <strong>an</strong>d<br />

the rotor core c<strong>an</strong> be found <strong>an</strong>d its boundary is shown as a dash line in the figure, where<br />

AB is in the <strong>stator</strong> core; O is the central point <strong>of</strong> <strong>stator</strong>; OA <strong>an</strong>d OB go through the rotor,<br />

the air gap <strong>an</strong>d the <strong>stator</strong> core <strong>an</strong>d c<strong>an</strong> be considered to be orthogonal to the inner surface<br />

<strong>of</strong> the <strong>stator</strong>. Based on the Ampere's Law, the magnetic field (H) <strong>of</strong> the boundary AOB<br />

c<strong>an</strong> be expressed in terms <strong>of</strong> the current density J, the differential length ∂l <strong>an</strong>d the area<br />

∂s as:<br />

∫<br />

C<br />

∫<br />

H ⋅ dl = J ⋅ ds<br />

(3.14)<br />

S<br />

If the turn function <strong>of</strong> <strong>an</strong> arbitrary <strong>winding</strong> A is ( θ )<br />

the inner surface <strong>of</strong> the <strong>stator</strong>, then equation (3.14) c<strong>an</strong> be written as:<br />

( ) iA<br />

91<br />

n A , where θ is the <strong>an</strong>gle around<br />

∫ H ⋅ dl = nA<br />

θ ⋅<br />

C<br />

(3.15)<br />

There are two assumptions that need to be clarified before the next step. The first one<br />

is: The air gap is so small compared to the <strong>stator</strong> or the rotor core that the magnetic field<br />

in the air gap c<strong>an</strong> be considered to be orthogonal to the inner surface <strong>of</strong> the <strong>stator</strong>. This is<br />

a very fundamental assumption in electric machine <strong>an</strong>alysis. The second one is:

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