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Analysis of Induction Motor Design and Simulation Problems

Motors and generators with MotorSolve

MotorSolve IM offers four types of analysis options; Equivalent circuit based analysis, AC analysis, PWM and Motion analysis. At different degrees of approximation, complexity and utility, they offer solutions to a wide variety of induction motor design and simulation problems. In this application page, some simple examples of the utility of these methods are presented (shown on the right are the bar currents of a 17 bar-24 slot squirrel cage induction machine computed using the PWM analysis option in MotorSolve IM).

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METHODS and RESULTS

DEEP BAR EFFECT

Because of its utility, the deep bar effect is an important phenomenon for induction motors. In this example, the deep bar effect of a 17 bar - 24 slot squirrel cage machine is illustrated using the AC analysis option in MotorSolve IM. The figure to the left shows the MotorSolve IM model for which the deep bar effect is computed.

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FLUX LINE CONTOURS and CURRENT DENSITY at 5% and 95% SLIP

The effect is shown in the figure to the left. The figure shows flux line contours and the current density at 5% slip (the left half) and at 95% slip (the right half). The results show that at low slip, the flux linkage is much better than that at 95% slip and also the current density is fairly uniformly distributed at 5% slip whereas at 95% slip, skin effects are prominent, as expected.

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SKEWING the IM

Cogging effects in induction motors are usually reduced by applying skewing to the rotor. In this example, MotorSolve IM's ability to take skewing into account is shown. The model used here is that in the figure to the left, a 17 bar - 24 slot machine, rated at 1800 rpm synchronous speed and 3% slip.

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DIFFERENCE in TORQUE RIPPLE between the SKEWED and UNSKEWED MODEL

The results are shown in the figure to the left. The difference in torque ripple between the skewed and unskewed model is clearly seen. These results were obtained using the Motion analysis and the ideal drive PWM simulations.

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FINE TUNING and DESIGN VERIFICATION

Fine tuning and design verification using FEA is another important design step for induction motors. The motion analysis option in MotorSolve IM offers this option. The example here demonstrates this.

Consider the same motor model as above. The rotor bar conductor area of the motor has been varied from 70 mm2 to 107 mm2. The percentage difference in the output torque between AC analysis and motion analysis are presented in the figure to the right. The results show that at high conductor bar area the error between the two analysis methods become significant enough that FEA based analysis (without any approximation) becomes necessary for fine tuning the model.

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