Dynamic and Thermal Modelling of Induction Machine with Non-Linear Effects

Okoro, Ogbonnaya

kassel university press, ISBN: 978-3-89958-003-7, 2002, 154 Pages

URN: urn:nbn:de:0002-0036

Zugl.: Kassel, Univ., Diss. 2002

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Content: The dynamic modelling of induction machines involves the development of accurate and reliable models that can adequately account for the machine’s non-linearities as a result of saturation effect, skin-effect and thermal effect with the view of realising the actual machine performance in transient conditions.

The work presents the modelling of the Squirrel-cage rotor bar. To effectively account for Skin-effect in the rotor bar, a T-network lumped parameter model is developed. An optimisation algorithm which provides a good correlation between the actual bar impedance and the model impedance for varying frequency at approximately 6% error is achieved. The work also develops mathematical models which include saturation effect or /and Skin-effect –features that are usually neglected in the development of the conventional model. The non-linear differential equations governing the transient behaviour of the test machine are derived and expressed in state variable form. The machine parameters are determined by carrying out D.C. measurement test, No-Load test, Blocked-Rotor test and Retardation test on the machine. MATLAB Programs are developed and used to solve the steady and transient mathematical models of the machine. A comparison between the predicted transient torque and speed in the conventional model and that with Skin or/and Saturation effects shows a remarkable difference. The simulated machine model with both skin-effect and saturation effect included gives a better result than the other models when compared with the measured machine transient performances at run-up condition and can therefore be conveniently used to predict the actual machine performances.

The study also investigates the estimation of induction machine mean temperatures at different parts. Thermal network model is developed and the resulting algebraic and differential equations solved in order to determine the thermal behaviour of the machine under steady and transient conditions respectively. It is observed that the computed mean temperatures of the machine parts at No-load, rated load and blocked rotor operations compare satisfactorily well with the measured temperatures.

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