Overview

Induction motors are widely used for industrial products and appliances to take advantage of benefits from the simple structure and affordability to maintainability. The rotating magnetic field of the stator winding induces a current in the secondary conductor. That current and the rotating magnetic field produce force in the rotation direction that turns the induction motor. However, the induced current generates a large amount of heat due to Joule losses in the rotor.
A coupled analysis is advantageous to precisely evaluate the temperature rise caused by these Joule and iron losses of induction motors. This type of simulation obtains the temperature distribution using thermal analyses that reference the loss density distribution obtained by magnetic field analyses. Designers can use the results to clearly review the overall temperature distribution as well as identify hot spots. JMAG can simulate ventilation cooling via flow and thermal circuits.
This case study evaluates the temperature variations when using two different fans in an induction motor by taking into account the ventilation cooling.

Fan Characteristics

This section compares the cooling results of two types of fans. Fig. 1 presents the PQ curves for Fan A and Fan B at 2,500 r/min. Fig 2. provides a conceptual diagram of the air ventilation produced by the fans. The PQ curve scales with the rotation speed to evaluate temperatures during the analysis.

Efficiency Maps, Losses, Temperatures, and Flow Rate

Fig. 3 presents the efficiency map and illustrates the operating points to evaluate the temperature. Table 1 shows the losses at each operating point. Fig. 4 indicates the flow rate of air for each fan through the rotor core ducts, stator core ducts, and gaps. Fig. 5 presents the operating points on the PQ curve for each rotation speed of the temperature evaluation. Fig 6 illustrates the part temperature variations for each fan.
We can review the efficiency of the induction motor using the results in Fig. 1. The analysis evaluates temperatures at the operating points with high efficiency. As outlined by Table 1, the losses act as the heat sources increasing the temperature.
The gaps have the smallest and the stator core ducts the highest flow rates as illustrated by Fig. 4. Fan B also produces a larger flow rate than Fan A.
As shown by Fig. 6, Fan A has a steady-state temperature of 235 deg C in the cage and 134 deg C in the coil. Fan B has a steady-state temperature of 163 deg C in the cage and 111 deg C in the coil. The temperature is lower with Fan B because Fan B has a larger flow rate than Fan A.