Thermal Analysis of Electric Machines Motor-CAD

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1 Thermal Analysis of Electric Machines Motor-CAD Create, Design, Engineer! 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 2 1

2 similar 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 Thermal Network Analysis 3 3 MotorCAD Motor Types Brushless Permanent Magnet (BPM) Induction (IM) Switched Reluctance (SRM) 5 2

3 MotorCAD Motor Types Brush Motor PMDC Inside Out (BPM-OR) Claw Pole (CLW) Synchronous Motor (SYNC 6 Motor-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 Cooling Types 8 3

4 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 9 Steady State or Transient Steady-State schematic diagram eases understanding 10 4

5 Steady State or Transient simple transient or complex duty cycle load analysis 11 Accurate results 12 5

6 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 crosssection 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 16 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 Ease of Inputs 17 6

7 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 nonoverlapping (bobbin) type endwindings 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 18 Select the Cooling Method Extensive range of cooling options available The heat transfer and flow network circuits are set up automatically based on the selection of cooling types used The 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 19 7

8 Losses are input for the following: copper iron windage bearings etc Losses 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 20 Material Thermal Properties The 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. 21 8

9 Material Database add new materials to the existing material database 22 Interface between two components with microscopic rough surfaces Interface Gaps Used to investigate the effect of interface gaps between components on thermal performance modeled as an effective airgap so giving physical insight to the user default settings are for a typical industrial machine extensive 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 23 9

10 Through Ventilation Model Both the heat transfer and flow network analysis circuits are automatically set up and calculated for a through ventilated machine The user has several options for defining the air flow paths range of stator and rotor ducting designs 24 Motor Mounting Mounting can have a significant impact on thermal behavior 35% - 50% of total loss can be dissipated through the flange in servo motor designs NEMA 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 25 10

11 colour-coded to cross section editors options 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 Schematic Diagram In this example we see that the main component of resistance between housing and stator back iron is due to the effective interface gap 27 Node data put directly on motor crosssection to give a quick and easy method of visualizing the temperature distribution in the machine Node Temperatures 28 11

12 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 Inbuilt Sensitivity Analysis 29 Duty Cycle Thermal Transient Analysis here we see an example of dutycycle 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 30 12

13 Transient Soak Back Analysis winding turn off & take out of water (no loss/less cooling) housing 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? 33 Examples of Previous Motor-CAD Projects Motor 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 43 13

14 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 46 Motor-CAD in Use (Motor Miniaturization) 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

15 Motor-CAD in Use (Radial Fin Optimization) increased rating shown for fin design optimised using Motor-CAD 49 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 50 15

16 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 51 duct systems available: Through Ventilation model flow circuit automatically calculated 52 16

17 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 53 Motor-CAD in Use (Aerospace Duty Cycle Analysis) duty-cycle analysis on an aerospace application with a short term load requirement the motor needed to withstand two cycles 54 17

18 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 55 18