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an investigation of dual stator winding induction machines

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circuit model <strong>of</strong> <strong>an</strong> <strong>induction</strong> machine set forth in [3.5]. The induct<strong>an</strong>ce calculation has<br />

been carried out on a coil-to-coil basis. The <strong>stator</strong> <strong>winding</strong> <strong>of</strong> each phase <strong>an</strong>d rotor circuit<br />

are generally modeled as circuit m <strong>an</strong>d circuit n , which have k <strong>an</strong>d l coils respectively,<br />

then the induct<strong>an</strong>ce calculation between circuit m <strong>an</strong>d circuit n is given, which looks<br />

complicated. The input line-to-line voltages are the only excitation needed for this model.<br />

This model has been proven to be useful for fault <strong>an</strong>alysis where the fault occurs in the<br />

<strong>winding</strong> itself [3.5].<br />

Finite Element Analysis (FEA) is a well-known method <strong>of</strong> plotting the steady state<br />

magnetic fields <strong>of</strong> various parts <strong>of</strong> electric <strong>machines</strong>. Repeated <strong>an</strong>d time consuming<br />

simulations are needed, using FEA to obtain comprehensive perform<strong>an</strong>ce pr<strong>of</strong>iles <strong>of</strong><br />

electric <strong>machines</strong>. Although FEA yields very accurate results, its use to study the<br />

dynamics <strong>of</strong> electric <strong>machines</strong> <strong>an</strong>d <strong>machines</strong> with multiple <strong>winding</strong>s <strong>an</strong>d excitations <strong>of</strong><br />

different frequencies is still a tough task.<br />

Another adv<strong>an</strong>tage <strong>of</strong> the coupled-circuit model is the possibility <strong>of</strong> calculating the<br />

currents flowing in the component parts <strong>of</strong> the machine, such as <strong>stator</strong> coils <strong>an</strong>d rotor bars<br />

during tr<strong>an</strong>sient, dynamic <strong>an</strong>d steady state operating conditions. In view <strong>of</strong> this<br />

possibility, the approximate flux densities in the air gap <strong>an</strong>d cores <strong>of</strong> the machine c<strong>an</strong> be<br />

deduced.<br />

1.2.3 Machine Model under Eccentricity Conditions<br />

Induction <strong>machines</strong> have small air gap lengths, although the actual length may be<br />

variable. They usually assumed to be const<strong>an</strong>t for the purpose <strong>of</strong> ease <strong>of</strong> <strong>an</strong>alysis,<br />

however, the air-gap lengths <strong>of</strong> real <strong>machines</strong> are not const<strong>an</strong>t because <strong>of</strong> problems<br />

11

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