228 – Thermal Analysis of an Induction Motor

Model Data

Overview

An induction motors are widely used in everything from industrial machines to home appliances because they have a simple construction and are small, light, affordable, and maintenance-free. The rotating magnetic field of the stator coils causes induced current to flow in an auxiliary conductor, which exerts force on the rotor in the rotational direction and causes it to spin. Large joule heat is generated in the rotor due to induced current.
Using the iron loss results from a magnetic study of an induction machine we can start a thermal study allowing for a calculation of the temperature distribution in the machine. This will give us an idea of the areas where the temperature are going to be the highest.
In this example, we evaluate the temperature distribution of an induction machine with a slip of 0.1.

Losses in the Induction Machine

The first step is to do a steady state approximate study with a slip of 0.1. From this we can extract the joule losses in the induction machine. The fig. 1 and fig. 2 show respectively the joule loss density in the cage and in the stator’s winding. We note that most of the joule losses in the cage are located in the ring short circuiting the bars of the cage.
The Losses obtained in the stator and the rotor are displayed in fig. 3 and fig 4.

Thermal study

The thermal study uses the resulting losses of the previous magnetic and iron loss study as a heat sources. The steady state thermal study then calculates the temperature reparation in the induction machine.
Fig. 5 show the temperature in the stator. As the joule losses are quite high we observe that the coils are the highest temperature point at 70 deg C. On the other hand, fig. 6 shows the temperature in the rotor, which is quite high in the cage due to the high joule losses and also the difficulty to evacuate the heat as it is trapped in the stator this results in temperatures exceeding 90 deg C in the cage.

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