Latest posts by Vincent Marché (see all)
- Thermal Analysis of Electrical Equipment – Different Methods Review - February 1, 2018
- Coupling Flux FEA to AcuSolve CFD solution –Thermal Analysis of Electrical Equipment - February 6, 2018
- Computing Capacitances Matrix with Flux PEEC – Power Module Example - January 16, 2018
If you want to have more accurate results, the use of CFD analysis is the solution. With CFD code, the main benefit is that there is no more assumption on the exchange coefficients, you just represent the different elements of your motor, with for instance a fan on the shaft, a cooler with a velocity for the liquid, … It helps a lot in order to understand where is the flow, and to better understand critical areas where focus should be on to improve thermal exchange.
From Flux computation, for the chosen working condition at 900 rpm, we will extract average losses for magnet (due to eddy current), in coils (Joule losses), iron losses in stator and rotor. These values are nodal values corresponding to average losses over one electrical period. Dedicated menus have been developed in order to compute directly these values.
In AcuSolve, the geometry of the motor has to be described as well. In the specific case of this motor, the cooling is done with an external coolant, plus the use of oil in part of the casing. The different solid components are described.
AcuSolve can then be used in order to determine the behaviour of the fluid surrounding the solid components. Rotational effects are considered. Convection on outer surface can be determined. The losses imported from Flux can be read directly, with the possibility to scale, shift or rotate if periodicity is present. The total heat load in watts can also be applied (on coils for instance). A coolant liquid enters and exit with an external water jacket to help cool the motor at 35°C and 2.4 Gal/min. The rotation of the rotor is also taken into account by modifying fluid region adjacent to it.
The results allow to understand the flow in the water jacket, and also the temperature distribution in the different elements. There is an increase of 5 degrees between the input and the exit of the water jacket.
The temperature on the casing is shown on the next figure:
The main benefit is a better understanding of the flow inside and around the motor.
Thus we have seen that different methods are available in order to estimate the thermal behavior of electric motors. Each method can be used at different level of the motor design. The equivalent model is interesting at the early design stage in order to check basic working points, or duty cycles. The solving time is fast, allowing parametric design. When more accuracy is required, using finite elements is a good idea, in order to have a better knowledge of losses (iron losses , eddy current losses), and their impact on thermal analysis. The rise of temperature in different areas is also easier to understand and to follow with animation for instance. Then if designers want more accuracy, or to better understand the flow, they can combine FEA magnetics with CFD code. It takes more time to create projects and for the solving time. The use of distribution of computation allow decreasing dramatically the solving time.
A post by Patrick Lombard – Lead Application Specialist EM Solutions – Altair