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Create, Design, Engineer!

Thermal Analysis of Electric Machines

Motor-CAD

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Brief Look at MotorCAD

geometry input using dedicated editors

select materials, cooling options

All difficult heat transfer data calculated automatically

lumped circuit solved to calculate steady-state and transient performance

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Thermal Network Analysissimilar to electrical network

thermal resistances rather than electrical resistances

power sources rather than current sources (losses)

thermal capacitances rather than electrical capacitors

nodal temperatures rather than voltages

power flow through resistances rather than current

In Motor-CAD the thermal network is automatically set up based on the motor geometry and cooling type selected

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Brushless Permanent Magnet

(BPM)

Induction

(IM)

Switched Reluctance (SRM)

MotorCAD Motor Types

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MotorCAD Motor Types

Brush Motor PMDC

Inside Out (BPM-OR)

Claw Pole (CLW)

Synchronous Motor (SYNC

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Cooling TypesMotor-CAD includes proven models for an extensive range of cooling types Natural Convection (TENV)

• many housing design types Forced Convection – (TEFC)

• many fin channel design types Through Ventilation

• rotor and stator cooling ducts Open end-shield cooling Water Jackets

• many design types (axial and circumferential ducts)• stator and rotor water jackets

Submersible cooling Wet Rotor & Wet Stator cooling Spray Cooling Direct conductor cooling

• Slot water jacket Conduction

• Internal conduction and the effects of mounting Radiation

• Internal and external

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Housing Types

Many housing designs can be modeled and optimized

the designer selected a housing type that is appropriate for the cooling type to be used and then optimizes the dimensions, e.g. axial fin dimensions and spacing for a TEFC machine

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Steady State or Transient

Steady-State schematic diagram eases understanding

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Steady State or Transient

simple transient or complex duty cycle load analysis

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Accurate results

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Radial & Axial Cross-Section Editors

• Geometry is described using the dedicated radial & axial cross-section editors

– input the dimensions of the design under consideration

– both the radial and axial cross-section are defined because end effects such as gaps around the end winding can have a significant impact on cooling

• The editors provides visual feedback

– reduced incidence of input errors

– insight into importance of heat transfer paths

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Ease of Inputs

Drop down selection editors for geometric options magnet shape, bar shape, slot

types, etc.

Numeric editor for dimensions long parameter names help

identify parameter meaning, e.g. Slot Number

Help describing the parameter being pointed at give on status line

press F1 for more detailed help

Components are colour coded to Schematic Network diagram

import from SPEED software

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Winding Input• layered winding model used to:

– automatically calculate a set of thermal resistances from slot wall to winding hot-spot

– give visualization of the proportion of components in the slot (liner, copper, enamel, impregnation)

• models for overlapping or non-overlapping (bobbin) type end-windings

• slot fill or conductors per slot input options

• end winding fill or MLT input options• conductor size input or selected from

a wire table• able to easily model impregnation

goodness and its effect on temperature rise

• data can be imported from SPEED

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Select the Cooling Method

Extensive range of cooling options availableThe heat transfer and flow network circuits are set up automatically based on the selection of cooling types usedThe most appropriate algorithm used to calculate convection heat transfer & pressure drops are set up automatically in the Motor-CAD calculation

benefits from the extensive research on convection & flow analysis correlations done previously by Motor Design Ltd

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LossesLosses are input for the following:

copper iron windage bearings etc

Accuracy of temperature prediction depends on accuracy of loss prediction

Losses can be imported directly from SPEED software or come from FEA or test data

Algorithms built into Motor-CAD to model loss variation with temperature, speed and load

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Material Thermal PropertiesThe user can input a components material thermal data directly (thermal

conductivity, specific heat and density) or select a material from the built in database

The materials weight is calculated and used in thermal transient calculations• Adjustments can be made to weights if required, i.e. to account for terminal

boxes, etc.

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Material Database

add new materials to the existing material database

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Used to investigate the effect of interface gaps between components on thermal performance

modeled as an effective airgap so giving physical insight to the userdefault settings are for a typical industrial machineextensive testing has been done to set the default values for parameters in Motor-CAD

Using sensitivity analysis we can quickly and easily quantify the effect of manufacturing options and tolerances on the thermal performance

Interface GapsInterface between two components with microscopic rough surfaces

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Through Ventilation ModelBoth the heat transfer and flow network analysis circuits are automatically set up and calculated for a through ventilated machineThe user has several options for defining the air flow paths

– range of stator and rotor ducting designs

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Motor Mounting

Mounting can have a significant impact on thermal behavior35% - 50% of total loss can be dissipated through the flange in servo motor designsNEMA rating test method for flange/foot mounted motors allow the motor to be attached

to a plate these can be modeled in Motor-CAD

The mounting can also be modeled using a fixed temperature of a component or an amount of power input at a node

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Schematic Diagramcolour-coded to cross section editorsoptions to display

Resistance :• Label• Resistance value• Power Flow• Temp Difference

Node :• Label• Temperature value• Capacitance value

most nodes have more than one resistance between them

e.g. stator back iron thickness + interface gap + housing thickness

component values shown to help identify main cooling constraints

schematic show final results of a thermal calculation

In this example we see that the main component of resistance between housing and stator back iron is due to the effective interface gap

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Node TemperaturesNode data put directly on motor cross-

section to give a quick and easy method of visualizing the temperature distribution in the machine

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Inbuilt Sensitivity Analysis Motor-CAD’s multi-parametric solver capabilities with automated graphing is very useful to help identify the main constraints to cooling and for studying the effects of manufacturing options and tolerances on the cooling performance

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Duty Cycle Thermal Transient Analysis• here we see an example of duty-

cycle load analysis carried out in Motor-CAD

• the complex load is input using the duty cycle editor

– it can also be imported from Excel, Matlab, etc

• we have excellent agreement between the calculated thermal response and measured temperatures

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Transient Soak Back Analysis

Soak back analysis is important in applications such some aerospace machines soak back is used to check heating of the housing when the machine is turned off

• When turned off the losses are zero but any forced cooling of the machine also often stops such that the housing increases in temperature due to heat soaking back from the hot winding

Example shown above: motors driving propellers on a small submersible craft fitted with a camera there is very good cooling when the craft is moving under water to remove the craft from the water it is moved to surface and motors turned off the craft is then removed from water by operator the losses are now zero but the housing increases in temperature (soak back) Motor-CAD was used to ensure the housing is not too hot for safe handling?

winding

housing

turn off & take out of water (no loss/less cooling)

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Examples of Previous Motor-CAD ProjectsMotor Miniaturization

Improved Impregnation

Radial Cooling Fin Optimization

Axial Cooling Fin Optimization

Through Ventilation

Submersible Motor

Aerospace Duty Cycle Analysis

Automotive Duty Cycle Analysis

Automotive PMDC

Servo motor duty cycle analysis

Outer rotor BPM modelling

Transient winding faults

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Motor-CAD in Use (Motor Miniaturization)

Existing Motor:

50mm active length

130mm long housing

New Segmented Motor: 50mm active length 100mm long housing 34% more torque for same

temperature rise

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new potting/impregnation materials

previous materials: k = 0.2W/m/C: 6%-8% reduction in

temperature,

new materials: k = 1W/m/C (larger values now available):

15% reduction in temperature.

Motor-CAD in Use (Motor Miniaturization)

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Motor-CAD in Use (Radial Fin Optimization)

increased rating shown for fin design optimised using Motor-CAD

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Motor-CAD in Use (Some IMs modeled)Temp. of the winding predicted to within 5%

315mm Shaft Height, Cast Housing 200mm Shaft Height, Cast Housing

80mm Shaft Height, Aluminium Housing 480mm Diameter, Water Cooled

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Motor-CAD in Use (Through Ventilation model)Temp. of the winding predicted to within 2ºC

1150hp IM

Details in paper at ICEM 2002

Tw(test) = 157ºC

Tw(calc) = 159ºC

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Through Ventilation modelduct systems available:

flow circuit automatically calculated

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Motor-CAD in Use (Soak Back Analysis)

submersible analysis: good cooling when

moving under water motor turned off and

removed from water losses = 0 but

housing increases in temperature

safe handling?

winding

housing

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Motor-CAD in Use(Aerospace Duty Cycle Analysis)

the motor needed to withstand two cycles

duty-cycle analysis on an aerospace application with a short term load requirement

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Motor-CAD in Use(Automotive Duty Cycle Analysis)

automotive applications (power steering, braking, etc) can have very complex load cycles:

• Motor-CAD very useful here

• data can be created in Excel and imported into Motor-CAD