Heat dissipationLife span of the electrical machinesAvo R Design of Electrical Machines 2Industrial ElectricalEngineeringand AutomationPreviouslyEnergy loss in electriccircuitsqe=J2Energy loss in magnetic circuitsq

=ChB2f+Ce(Bf)2Energy loss in mechanic circuitsq

=Avo R Design of Electrical Machines 3Industrial ElectricalEngineeringand AutomationNextConductioncoolingConvectioncoolingRadiativecoolingThermal circuit and thermal designHeat sources, heat sinks andheat flow.Avo R Design of Electrical Machines 4Industrial ElectricalEngineeringand AutomationEvaluation of thermal loading Heat transfer Input: heat sources and cooling conditions Outcome: temperature distribution Computational tools Analytic, empiric, numeric FEA, CFD, lumped circuits for heat transfer and fluid flow Material characterization Sub-model validationAvo R Design of Electrical Machines 5Industrial ElectricalEngineeringand AutomationComplexity Electrical machine is A complex 3D electromagnetic structure A complex spatial fluid dynamic structure with cooling medium In order to determine the temperature distribution A good estimate of losses has to be known Properties of the cooling process has to be known The thermal characteristics and properties has to be known An optimized thermal design can help increase machine rated power substantiallyAvo R Design of Electrical Machines 6Industrial ElectricalEngineeringand AutomationThermal design Good estimate of losses the spatial and temporal distribution of heat sources Waveformof a loss origin Distribution of heat sources Duty cycle operationalcycle time often muchshorter than thermal time constant Short time operation Intermittent Thermal characteristics of materials Temperature dependence Temperature limits Heat dissipation thermal circuit and cooling system Thermal efficiency Cooling conditions (normal, forced) Maximumallowed loadingaccording to the thermal limits at cooling capabilityAvo R Design of Electrical Machines 7Industrial ElectricalEngineeringand AutomationThermal circuit heat carrier A good electricconductor is usually also a good thermalconductor Interested in hotspots: 100% conductor in the middle of winding Heat is taken from end-windings: conduction, convection or bothAvo R Design of Electrical Machines 8Industrial ElectricalEngineeringand AutomationThermal circuit thermal contacts A bad electric conductor is usually also a bad thermal conductor No air-gaps in electrical circuit, many air-gaps in thermal circuit Thermal contact between stator core and housing 0.1 mm +5K 0.2 mm +10KAvo R Design of Electrical Machines 9Industrial ElectricalEngineeringand AutomationDesign target - Thermal limits The most critical component in the electrical machine is insulation and temperature dependent is magnet. Insulation lifetime is shortened radically if temperature exceeds the limit and that is due to accelerated oxidation process in the insulation material. =100K -> lifetimeAvo R Design of Electrical Machines 10Industrial ElectricalEngineeringand AutomationTemperature dependence Materials temperature dependence is taken account with material thermal coefficients o( ) ( )coil coil coil coil coil 0 01 0 0 o + =( ) ( )magn magn Brmagn magn R RmagnB B0 01 0 0 o + =( ) ( )magn magn Hcmagn magn C CmagnH H0 01 0 0 o + =Avo R Design of Electrical Machines 11Industrial ElectricalEngineeringand AutomationHeat transfer Steady state and transient Heat transfer problem according to temperature (potential) and heat balance between source, sink and storage heat transfer convection-diffusion equation incompressible Navier-Stokes equations for fluid dynamics tc Qz y xQz y xp z y xz y xcc= +cc+cc+cc= +cc+cc+cc00000002222222222220( ) Q c ktcp p= + V V +ccu 0 00( )02= V+ V + V = V +ccuF u u uuq ptAvo R Design of Electrical Machines 12Industrial ElectricalEngineeringand AutomationEquivalent circuit relations=Q R N I = R U=I ROhms LawR=1/ l / A R=1/ l / A R=1/ l / AResistive elementQ=q A =B A I =J AFlow=G l N I =H l U=E lPotentialThermal circuitMagnetic circuitElectrical circuitRelationAvo R Design of Electrical Machines 13Industrial ElectricalEngineeringand AutomationEquivalent circuitAvo R Design of Electrical Machines 14Industrial ElectricalEngineeringand AutomationMulti-physics FEM Different problems in physics share the same geometry Calculate for a single element The variation of loss origin RMS power loss MEAN temperature A field equation is solved for the finite size of volume boundaries suppose to specify a potential (essential), flow naturally given. N1 (x 1 ,y1 )N 2(x 2 ,y2 )N 3(x 3 ,y3 )u1u3u5u2u4u6 13 2xy

fecup t z y x Bp t z y x J, , ,, , ,Avo R Design of Electrical Machines 15Industrial ElectricalEngineeringand AutomationThermal modelling example I Determine heat sources in regions Specifycooling conditions over cooling surfaces Find heat balance i.e. temperature distributionAvo R Design of Electrical Machines 16Industrial ElectricalEngineeringand AutomationThermal modelling example II Calculating flux (and current) density waveform Estimating losses densities in the symmetric part of machine Calculating temperature distribution according to heat sources and sinksAvo R Design of Electrical Machines 17Industrial ElectricalEngineeringand AutomationThermal modelling example IIIAvo R Design of Electrical Machines 18Industrial ElectricalEngineeringand AutomationThermal model Geometry of a PMSM Material & thermal loading Winding Permanent magnets Surface & cooling Natural convection Temperature nodes Nodes of interest Thermal circuits Heat transfer rather than flow network Thermal resistances Focus on thermal air-gaps

pm

win

surf

ambpmwinsurfamb

mw mw msmw mws wsms ws wsa sasa sak k kk k kk k k kk k

000 0pmwinQQ00

Avo R Design of Electrical Machines 19Industrial ElectricalEngineeringand AutomationModel development Sorces and loads Conductor losses Convection cooling 2D heat transfer Approximate rating Extraction of elements 3D heat transfer Extrucion from 2D Focus on end turns Heat exchange through end-turns Thermal conductionAvo R Design of Electrical Machines 20Industrial ElectricalEngineeringand AutomationThermal circuit cooling circuits Natural and Forced Integrated cooling as a result of machine integrated construction Slotted stator operates as a cooling circuit Directly cooled heat sources Cooling ducts, cooling jackets, cooling channels Cooling capability Maximize the coolingsurface area Improve cooling mediumparameters and velocity Smallest temperature rise is the goal when designing a thermal circuit Avo R Design of Electrical Machines 21Industrial ElectricalEngineeringand AutomationCooling Concepts Structure Where the energy conversion, heat transfer and temperature drop () takes place Heat sources Energy converted to heat Cooling sources Heat dissipation Cooling concepts arrangement of heating and cooling sources Indirect Cooling (high ) Direct cooling (low )Avo R Design of Electrical Machines 22Industrial ElectricalEngineeringand AutomationThermal conductivity Conduction is heat transfer by diffusion in a stationary medium due to a temperature gradient. The medium can be a solid, a liquid or gas Diffusion through the substancex

1

2 QAl 2 12 1

lAQlAQAvo R Design of Electrical Machines 23Industrial ElectricalEngineeringand AutomationThermal conductivity10 SmCo9 NdFeB 0.2 Avg.ins.system200-220 Aluminum 0.64 Bonding epoxy360 Copper 0.4-0.6 Mica20-40 Laminated iron 0.12 Kapton25-30 Stainless-steel 0.11 Nomex40-46 Cast iron 0.025-0.035 Air [W/m0K] Material[W/m0K] MaterialAvo R Design of Electrical Machines 24Industrial ElectricalEngineeringand AutomationModeling a winding Equivalent thermal conductivity of a winding is given by the filling factor of the conductor strands (copper in this example) and the thermal conductivity of the medium between the conductor strands ins condf cond f insinsfcondfeffk k L k L k LL

1 1 f cond f insins condeffk k

1

Avo R Design of Electrical Machines 25Industrial ElectricalEngineeringand AutomationConvection( ) ( )amb nh k n q 0 0 0 = V = Convection is heat transfer between either a hot surface and a cold moving fluid or a cold surface and a hot moving fluid. Convection occurs in liquids and gases Movement of the substancex 01 002

1Q A 0amb 0hot

2 l( )( )amb hotamblAQA Q0 0o o0 0 o+ += =2 12 21 1Avo R Design of Electrical Machines 26Industrial ElectricalEngineeringand AutomationTransport of heatQ - the required flow rate, m3/s, Ph- required cooling power, W,- the density of the heat carrier, kg/m3, c - the specific heat capacity, J /kgC,- the temperature difference between incoming and outgoing temperature CNatural convectionForced cooled plane surface by air speed vEmpirical cooling capability

cPQh225 5m KW

78 . 0 6 . 020 8 . 7

v 25 . 2 1mkWAPcoolloss Avo R Design of Electrical Machines 27Industrial ElectricalEngineeringand AutomationRadiation Radiation is heat transfer between cooling surface A at temperature 02and ambience at temperature 0ambvia electromagnetic waves ambambradradambradcA c Q0 00 0o0 0||.|

\||.|

\| |.|

\|=||.|

\||.|

\||.|

\|=24 4224 42100 100100 100x 01 002

1Q A 0amb 0hot

2 lAvo R Design of Electrical Machines 28Industrial ElectricalEngineeringand AutomationTransient heat flow Steady state temperature Heating time constant Temperature rise during the transient heatingx01 0

1A0amb 0hot

2lQPQSQD02 0 o00 0 + =+ =+ =2Adtdc V PR dtdC PQ Q QththD S P( )||.|

\| + = = == =tamb m ambth th thth mtheAc VR CAPR Pt0 0 0 0oto0122Avo R Design of Electrical Machines 29Industrial ElectricalEngineeringand AutomationTransient heat flow Thermal model representing a physical model Mathematical formulation Many simplifications and approximations Heat is not internally generated in the body Losses are applied to specific node-point

1 Rth

2 Cth P 211 21 21

avth th thC R CPdtdAvo R Design of Electrical Machines 30Industrial ElectricalEngineeringand AutomationHome assignment 3 PMSM model based on lumped equivalent circuits Magnetic thermal Core loss modelling Data input Models Thermal limits and peak/nominal operation pointsAvo R Design of Electrical Machines 31Industrial ElectricalEngineeringand AutomationThermal circuit at steady state Node points i, Qi[W], i[K]5. Coil loss and temperature4. Tooth loss and temperature6. Yoke loss and temperature7. 8. Ambience temperature Thermal conductivity elements Gij[W/K] From coil to tooth G54 From coil to yoke G56 From tooth to yoke G46 From yoke to ambience G67Avo R Design of Electrical Machines 32Industrial ElectricalEngineeringand AutomationSummary Thermal constrains and dependences Thermal circuits, heat sources and cooling options Heat transfer model and modelling Learning skills from the assignmentsBHcDoBA