Challenges in Cooling of Electrical Machines

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1 Challenges in Cooling of Electrical Machines Rafał Wróbel 1

2 What are the electrical machines? electromechanical transducers Some Fundamentals allowing to convert electrical energy to mechanical motion or vice versa (motors and generators) electromagnetic transducers allowing to transform selected attributes of electrical energy, e.g. voltage, current, frequency (transformers and inductors) 2

3 Rotary Machine Assembly What is a typical machine construction? 3

4 Rotary Machine Assembly What is a typical machine construction? End cap Housing Stator Bearing Winding Rotor Shaft 4

5 Stator Construction Let s have a closer look at a common statorwinding arrangement, Impregnation Core pack Housing Cavities Conductor Enamel Winding 5

6 Stator Construction Let s have a closer look at a common statorwinding arrangement, Impregnation Cavities Conductor Enamel Air (1atm), Core pack 0.033W/m K Liner (Nomex410), 0.121W/m K Housing Varnish, 0.44W/m K Epoxy (Staycast), 1.30W/m K Steel (3% SiFe), 22.0W/m K Aluminium (pure), 200W/m K Copper(pure), 400W/m K Winding 6

7 And, a closeup at a rotor with permanent magnets (PMs), Shaft Rotor Construction Stator Cut outs PM segments Core pack Rotor 7

8 Some other machine types, Switched reluctance machine Machine Topologies Salient pole wound field machine Induction machine Variable reluctance machine 8

9 Variety of Machine Designs Are the design targets universal across wide range of electrical machines? Output power, 7.5mW Rotational speed, 72krmp Efficiency, 18% Voltage, 3V O/D < 2mm Weight, 190mg by Namiki 9

10 Variety of Machine Designs Are the design targets universal across wide range of electrical machines? Output power, 7.5mW Output power, 2000MW Rotational speed, 72krmpRotational speed, 1.5krmp Efficiency, 18% Efficiency, 99% Voltage, 3V Voltage, 27kV O/D < 2mm O/D, meters Weight, 190mg Weight, tonnes by Siemens by Namiki 10

11 Design for Application What are the key considerations when designing a new machine? electromagnetic design thermal design mechanical design Performance Cost Manufacture Life 11

12 Power Loss Components What are the main power loss components generated within an electrical machine? electromagnetic winding loss core loss permanent magnet loss mechanical bearing loss windage and drag loss 12

13 Power Loss Components What are the main power loss components generated within an electrical winding machine? topology, electromagnetic Ac effects associated with conductor arrangement winding Effects loss related Difficult to with processing core loss assess or and in-application permanent magnet loss validate use of the core experimentally mechanical material Challenging to predict in bearing loss situ behaviour, windage and drag lossaccounting for bearing Computationally assembly expensive 15 May

14 Heat Transfer Mechanisms What are the key heat transfer mechanisms in an electrical machine? conduction convection radiation contact thermal resistance 14

15 Heat Transfer Mechanisms Difficult to predict What are the key heat transfer for composite mechanisms in an electrical machine? materials, e.g. conduction impregnated winding assembly convection Challenging radiationto estimate Frequently of theoretically contact thermal resistance lesser importance Impossible to predict theoretically 15

16 Heat Extraction Techniques What are the existing heat evacuation methods in electrical machines? passive usually fully enclosed machine designs for less demanding applications or where the active cooling is infeasible active indirect and/or direct fluid cooling of the machine outer periphery and/or active parts (heat sources) respectively 16

17 Some Laboratory Examples Forced convection with liquid cooling Natural convection Enhanced conduction with liquid cooling Forced convection with air cooling 17

18 Selected Design Challenges So, what are the design challenges for the next generation of electrical machines? design for high-specific-output, high-speed, lightweight, compact, high-efficiency, robust and reliable operation integrated and/or multifunctional motor drives, e.g. electrical machine combined with power electronics repeatable, in-volume, low-cost manufacture design solutions rapid and reliable Design for Application design process 18

19 Enabling Technologies What are the key factors enabling the next generation of electrical machines? application of new more reliable and accurate, fully informed design process implementation of new materials, e.g. super conductors, phase change materials, composite materials, etc. use of new manufacturing techniques, e.g. additive manufacture 19

20 Commercial Examples Liquid cooled housing Rotor Stator by Porsche 20

21 Commercial Examples Stator Air cooled housing Rotor by Protean 21

22 Commercial Examples by GM Liquid cooled housing Stator Rotor 22

23 Commercial Examples by Nissan Stator Rotor Liquid cooled housing 23

24 Commercial Examples Stator Rotor Liquid cooled housing by Toyota 24

25 Commercial Examples Rotor by Tesla Stator Liquid cooled housing and rotor 25

26 Commercial Examples Rotor Stator Liquid cooled winding by Yasa 26

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