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an investigation of dual stator winding induction machines

an investigation of dual stator winding induction machines

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o<br />

Figure 3.1 General diagram for <strong>an</strong> electric machine showing non-const<strong>an</strong>t air gap length<br />

The permeability <strong>of</strong> iron is much greater th<strong>an</strong> that <strong>of</strong> air, hence the magneto-motive force<br />

drops on the <strong>stator</strong> <strong>an</strong>d the rotor cores c<strong>an</strong> be ignored. A general definition for the air gap<br />

is expressed as [3.9]:<br />

( θ θ ) g [ 1−<br />

a cos(<br />

θ + γ ) − a ( θ −θ<br />

+ γ ) ]<br />

g cos<br />

, rm = 0 1<br />

2<br />

rm<br />

(3.16)<br />

where, 1 a <strong>an</strong>d 2<br />

a are const<strong>an</strong>ts, which represent the degree <strong>of</strong> static <strong>an</strong>d dynamic<br />

eccentricity respectively; θ rm is the rotor mech<strong>an</strong>ical <strong>an</strong>gle; g 0 is the average air gap<br />

length <strong>an</strong>d <strong>an</strong>gle γ defines the ch<strong>an</strong>ges <strong>of</strong> the distribution <strong>of</strong> the air gap length around<br />

the inner <strong>stator</strong> surface.<br />

It is clear from (3.16) that the air gap length not only depends on the <strong>an</strong>gle around the<br />

<strong>stator</strong>, but also on the rotor <strong>an</strong>gle, which will be true under almost all possible conditions.<br />

The const<strong>an</strong>t air gap length condition c<strong>an</strong> be achieved by setting a 1 <strong>an</strong>d a 2 to be zero.<br />

Applying the above two assumptions to equation (3.15), the integration part <strong>of</strong> the<br />

equation (3.15) c<strong>an</strong> be restated as:<br />

92<br />

A<br />

B

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