# Generic information

## 1. Limitation of thermal computations – Advices for use

## 1.1 General understanding of the results

FluxMotor thermal model provides the mean temperatures of every component of the machine.

The computation does not consider:

- The hot spots linked to local phenomena, for instance between two conductors in the winding.
- The hot spots linked to the machine position (horizontal, or vertical). The motor position set by the user in COOLING subset, EXTERNAL panel, is only considered to compute the external convection occurring on the frame. The temperature difference between the upper components and the lower components of the machine is neglected.
- The machine is assumed to be connected to the external environment only through the frame, itself thereby only extracting the heat to the external fluid and to the cooling circuit fluid. It is assumed that no conduction occurs outside of the represented geometry in FluxMotor. FluxMotor model then neglects the following cooling effects:

The conduction through the shaft extension until external components, as a load

The conduction through the fixation of the machine on the ground, or on a plate.

## 1.2 End winding temperatures

End winding geometry is complex, and many hot spots can exist in this specific part of the machine.

FluxMotor computes an estimation of the mean temperature occurring on the Connection Side and Opposite Connection Side end windings.

Keep in mind that the real temperatures reached in such non-homogeneous regions can be far from the estimation, depending of the winding manufacturing.

## 1.3 Natural convection on end windings

When choosing to model that the end spaces are cooled with natural convection, FluxMotor model uses a quite low rotor tip speed ratio (a value of 5) to describe the fluid velocity far from the rotating components.

This can lead to overestimates the cooling of the end winding on high-speed machines. This model will be improved for future versions.

When a tip speed ratio of 5 seems to overestimate the end winding cooling, it is advised to switch to forced convection mode.

This mode allows to force some higher tip speed ratios for areas far from the rotor, this reducing the efficiency of the cooling on the end winding.

## 1.4 Temperatures considered for fluidic computations

Some fluidic computations are based on two different temperatures: the temperature of the fluid, and the temperature of the wall from where the convection occurs.

This explains that the convection results shown in the design environment can be slightly different from the results obtained in the test environment.

In the design environment, the fluid and the wall are at the evaluation temperature, but in the test the wall and the fluid temperatures are evaluated during the solving and are different in most of the cases.

## 1.5 User parts in thermal computations

User parts can be used for thermal computations, as for magnetic computations.

However, a general warning must be kept in mind when building a part to use it for thermal computations.

The thermal computation is based on a finite element thermal project, where a thermal network is identified from the geometry given by the user.

On a user part, every face defined by the user will be a « node » of the thermal mesh that the process identifies on the part.

To have consistent results, be careful when defining the part that:

- There is no face surrounding another one, this giving inconsistent network.
- The faces are as much as possible close to standard shapes, likes rectangles or triangles.

On the other hand, keep in mind that the interface gaps defined in the part are only used for magnetic applications. Only the interface thicknesses defined in the COOLING subset, INTERNAL panel, are considered for thermal computations.

The thermal resistances corresponding to the interface thicknesses are computed considering that the interfaces are made of air at 273.15 Kelvin and at the atmospheric pressure at sea level, 1.013E5 Pa.

## 1.6 Assumption on the geometry of the shaft, the lamination, and the frame for thermal computations

The possible air areas existing between the stator lamination and the frame are not considered in FluxMotor thermal computations. This means that the case of a circular stator lamination, or lamination with chamfer, in contact with a square frame, is not considered.

The assumption is made that there is no gap in the conduction between the stator yoke and the frame: if a square frame is set, the computation considers that the lamination is rectangular as well, without chamfer or fillet.

It is also assumed that there is conduction through each part of the shaft until rear and front bearing (even in the case where the modeled shaft in FluxMotor is not in contact with the frame.

In addition, the lamination extension, available in previous version, is equal to zero in the thermal computations.