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an investigation of dual stator winding induction machines

an investigation of dual stator winding induction machines

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This expression shows that <strong>an</strong> additional electric field will be induced by a time<br />

varying magnetic field <strong>an</strong>d consequently a voltage is produced in a closed coil placed in<br />

the magnetic field. If the Electro-Motive Force (EMF) in equation (3.12) is replaced by<br />

the negative <strong>of</strong> the voltage − v , a conventional expression will be found as:<br />

dψ<br />

v = (3.13)<br />

dt<br />

3.3 General Winding Function Expression<br />

The <strong>winding</strong> function theory which is used to calculate the induct<strong>an</strong>ces <strong>of</strong> <strong>induction</strong><br />

<strong>machines</strong> was developed in the 1960's. The <strong>winding</strong> function theory has been used with<br />

success to calculate the induct<strong>an</strong>ces <strong>of</strong> <strong>induction</strong> <strong>an</strong>d synchronous <strong>machines</strong> with<br />

const<strong>an</strong>t or variable air gap length with or without rotor eccentricities [3.6-3.8]. It c<strong>an</strong> be<br />

found from previously published papers that the <strong>winding</strong> function is only considered after<br />

the average <strong>of</strong> the turn function is removed from itself. This <strong>winding</strong> function definition<br />

yields correct results when the air gap <strong>of</strong> the machine is const<strong>an</strong>t around the inner surface<br />

<strong>of</strong> the <strong>stator</strong>. However, if the same definition <strong>of</strong> the <strong>winding</strong> function is applied under<br />

rotor eccentricity conditions, in which the air gap length <strong>of</strong> the machine is no longer<br />

const<strong>an</strong>t, the equality <strong>of</strong> L 12 = L21<br />

= L c<strong>an</strong>not be observed by using the <strong>winding</strong><br />

function definition for induct<strong>an</strong>ce calculation under rotor eccentricity conditions. This<br />

inequality, which does not agree with the equality that we c<strong>an</strong> find in the linear magnetic<br />

circuit, was first reported in [3.7]. It is very difficult to find a proper expl<strong>an</strong>ation for this<br />

inequality. As a result, a method called the modified <strong>winding</strong> function approach <strong>an</strong>d<br />

extension <strong>of</strong> <strong>winding</strong> function theory were proposed in [3.8, 3.9]. The <strong>winding</strong> function<br />

90

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