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an investigation of dual stator winding induction machines

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202 V respectively. After the machine has achieved steady state operating condition at<br />

0.4 second, a 3 Nm (rated load) load is added to the machine to stimulate a dynamic<br />

response. The simulation results for dynamic responses <strong>of</strong> the machine are shown in<br />

Figure 4.29 <strong>an</strong>d the corresponding rotor bar currents are shown in Figure 4.31. When the<br />

simulation results are compared to those when the air-gap length is const<strong>an</strong>t, it is<br />

observed in the waveforms <strong>of</strong> the developed electromagnetic torque, rotor currents <strong>an</strong>d<br />

the <strong>stator</strong> currents that the waveforms under the mixed eccentricity condition contain<br />

more harmonic components. The <strong>stator</strong> currents for both the ABC <strong>winding</strong> set <strong>an</strong>d the<br />

XYZ <strong>winding</strong> set are not pure sinusoidal under no load steady state condition <strong>an</strong>d the<br />

current waveforms are not improved under the rated load condition. Obviously a<br />

pulsation torque component is observed in the waveform <strong>of</strong> the electromagnetic torque<br />

under the rated load condition. All the simulation results show that under rotor<br />

eccentricity conditions, more harmonic components appear in the machine developed<br />

electromagnetic torque <strong>an</strong>d currents; harmonic components which c<strong>an</strong> be used to<br />

diagnose the state <strong>of</strong> health <strong>of</strong> the <strong>dual</strong> <strong>stator</strong> <strong>winding</strong> <strong>induction</strong> <strong>machines</strong>. From the<br />

simulation results, the harmonic content <strong>of</strong> the current waveforms <strong>of</strong> the 2-pole <strong>stator</strong> set<br />

<strong>of</strong> <strong>winding</strong>s are higher th<strong>an</strong> those <strong>of</strong> the 6-pole <strong>stator</strong> <strong>winding</strong> set due to the frequency<br />

component match <strong>of</strong> the 2-pole <strong>winding</strong> set distribution <strong>an</strong>d the approximate inverse gap<br />

function. Similar frequency component match, leading to increased harmonic current<br />

magnitude is also possible for the 6-pole <strong>winding</strong> set distribution if the approximate<br />

inverse gap function contains commensurate higher frequency components. However, the<br />

influence <strong>of</strong> this interaction is not as signific<strong>an</strong>t in the 6-pole <strong>winding</strong> set. In general,<br />

harmonic currents are obtained due to the harmonics in the induct<strong>an</strong>ces; they decrease as<br />

184

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