Embed Size (px)
Citation preview
Electric Motor Thermal Management R&D
Kevin Bennion, Emily Cousineau, Xuhui Feng, Charlie King, Gilbert Moreno
National Renewable Energy Laboratory
IEEE Power & Energy Society General Meeting
Denver, CO July 26-30, 2015
1
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and
Renewable Energy, operated by the Alliance for Sustainable Energy LLC.
Relevance – Why Motor Cooling • Current Density
• Magnet Cost
• Price variability
• Rare-earth materials
• Material Costs
• Reliability
• Efficiency
• Temperature Distribution
Stator Cooling Jacket
Stator End-Winding
Rotor Stator
Sample electric traction drive motor
Photo Credit: Kevin Bennion, NREL
Photo Credit: Kevin Bennion, NREL
2
Passive and Active Cooling
3
Passive Thermal Design
Active Convective
Cooling
Motor Thermal
Management
Passive Thermal Design
• Motor geometry
• Material thermal properties
• Thermal interfaces
Active Convective Cooling
• Available coolant
• Cooling location
• Parasitic power
• Heat transfer coefficients
3
Passive Thermal Design
4
Slot Windings
Thermal Contact
Resistance
Slot Paper
Stator Laminations Measure
• Material thermal properties
• Thermal interfaces
Cold Plate
Hot Plate
Copper Spreader
Copper Spreader
Copper Metering Block
Copper Metering Block
Test Sample
Thermal Grease
Thermal Grease
Force Applied
Test apparatus built in accordance with ASTM
D5470-12 steady state technique
Thermal Contact Resistance
0
50
100
150
200
250
300
138 276 414 552
Inte
rlam
inat
ion
Th
erm
al C
on
tact
R
esi
stan
ce (
RC)
[mm
²-K
/W]
Clamping Pressure [kPa]
M19 29 Gauge
M19 26 Gauge
HF10
Arnon 7
Ridged Average
Smooth Average
Ridged
Smooth
Photo
Cre
dit: E
mily
Cousin
eau
Full technical report available at:
www.nrel.gov/publications/
5
Lamination Thermal Conductivity
0.0
0.5
1.0
1.5
2.0
138 276 414 552Effe
ctiv
e T
hro
ugh
-Sta
ck T
he
rmal
C
on
du
ctiv
ity
[W/m
-K]
Pressure [kPa]
M19 26 Gauge
M19 29 Gauge
HF10
Arnon7
𝑘𝑒𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 =𝑡
𝑅𝐶 + 𝑅𝐿
keffective = effective thermal conductivity
t = thickness of one lamination
RC = thermal contact resistance
RL = thermal resistance of one lamination
• Thinner laminations
have more contacts per
unit length
• Higher pressure lowers
contact resistance
• Error bars represent
95% confidence interval
Full technical report available at:
www.nrel.gov/publications/
6
Slot Materials and Interfaces Slot Winding
(paper bonded)
Slot Winding
(paper removed)
Slot Paper
Photo
Cre
dit: E
mily
Cousin
eau,
NR
EL
7
Slot Materials and Interfaces
• Preliminary results indicate substantial thermal resistance present between slot winding and paper
• Preliminary results measured to be 1,800 mm²-K/W
• As large as or larger than the slot liner paper alone (1,676 mm²-K/W )
• More tests are necessary to confirm results and reduce measurement uncertainty
• Contact resistance between paper and stator may also be significant
Paper
8
Active Convective Cooling
Measure heat transfer coefficients
for ATF cooling of end windings
Direct impingement on target surfaces
Impingement on motor end- windings
Average Heat Transfer Coefficients • Establish credibility of experiment and data with comparison of flat target
surface results to existing correlations in literature • Produce new data for textured surfaces representative of end-winding wires
Spatial Mapping of Convective Heat Transfer Coefficient • Jet local convective heat transfer • Large-scale end-winding convective heat transfer mapping
Photo Credit: Jana Jeffers, NREL Photo Credit: Kevin Bennion, NREL
ATF: automatic transmission fluid
9
Average Heat Transfer Coefficients D (mm) d (mm) S (mm) S /d D/d
12.7 2.06 10 5 6.2
Test Sample
Nozzle Plate:
Orifice Diameter
(d) = 2 mm
Sample Holder/Insulation
Resistance
Heater Assembly
Fluid Inlet
Aluminum
Vessel
Thermocouples
S = 10 mm
D = 12.7 mm
Oil impingement test section schematic (left). Photo during operation (right).
Photo Credit: Jana Jeffers, NREL
10
10
ATF Impingement Target Surfaces
Baseline 18 AWG 22 AWG 26 AWG
Radius (wire and insulation),
mmN/A 0.547 0.351 0.226
Total wetted surface area, mm2 126.7 148.2 143.3 139.2
• ATF impingement baseline target is flat polished copper with 600-grit sandpaper
• Additional targets mimic wire bundles with insulation (18, 22, and 26 AWG)
AWG = American wire gauge
18 AWG 22 AWG 26 AWG Credit: Gilbert Moreno, NREL
11
11
Comparison to Plain Surface Correlations
ATF fluid properties provided by Ford.
12
Heat transfer coefficients of all target
surfaces at 50°C inlet temperature
• At lower impingement
velocities, all samples achieve
similar heat transfer
• Average heat transfer
coefficients increase with
larger wetted areas based on
wire size
Note: Heat transfer coefficient calculated from the base projected area (not wetted area).
50°C Inlet Temperature
0
2,000
4,000
6,000
8,000
10,000
12,000
0 2 4 6 8 10 12
He
at T
ran
sfe
r C
oef
fici
en
t [W
/m2K
]
Velocity [m/s]
18 AWG
22 AWG
26 AWG
Baseline
ATF Heat Transfer Coefficients
13
13
ATF Heat Transfer Coefficients • Fluid splatter observed at higher velocities for 70°C and 90°C inlet liquid temperatures
• Splatter at 90°C occurred at lower velocity than at 70°C
• As temperature increases, it is expected that the fluid splatter will occur at lower velocities
ATF flowing over surface
ATF deflecting off surface
Note: ATF viscosity decreases as temperature increases.
0
2,000
4,000
6,000
8,000
10,000
12,000
0 2 4 6 8 10 12
He
at T
ran
sfe
r C
oef
fici
en
t [W
/m2K
]
Velocity [m/s]
50°C70°C90°C
18 AWG sample data for all inlet temperatures
Photo
Cre
dits:
Jana J
effers
, N
RE
L
14
Spatial Mapping of Heat Transfer
• Not all motor end-winding surfaces are directly impacted by ATF jets
• It is important to map the spatial distribution of the heat transfer coefficients to know the overall cooling effect
ATF jet more cooling
less cooling
Photo Credit: Kevin Bennion, NREL
15
Local Convective Heat Transfer Spatial mapping of local heat transfer with
ATF jet impingement:
• Jet impingement heat transfer coefficients are not uniform over the entire cooled surface
• The rate of decrease in the heat transfer coefficient is unknown
Heated surface
Stagnation zone
Wall jet zone
d, nozzle
diameter
Tw
Liquid jet
Air
r / d
Heat transfer coefficient
Experimental velocity profile of jet
impingement showing variation in
velocity at target surface. Measured
using particle image velocimetry
(PIV) at NREL.
Jet
Wall or Target
Boundary
Radial Distance
Nozzle
16
Local Convective Heat Transfer
Built test apparatus to
spatially map local heat
transfer coefficients with ATF
jet impingement.
Foil: heated via joule
heating
Lexan
insulation/support
Bus bars
Test article cross-sectional view
Teflon insulation/
support
Assembled test article View of the TLC-coated foil
Photo Credits: Gilbert Moreno, NREL
TLC: thermochromic liquid crystals
17
Large-Scale Heat Transfer
Spatial mapping of large-scale end-winding convective heat
transfer with direct ATF cooling
Stator winding removed for
sensor package
3D drawing of stator with
sensor packages installed
Photo Credits: Kevin Bennion, NREL
Photo Credit: Kevin Bennion, NREL
18
Sensor Design
Flat 18 AWG 20 AWG
Sensor
Package
Targets
Exploded View
19
Spatial Mapping of Heat Transfer
ATF
jets
2
1 1. Fluid Jet Geometry
• Location and
orientation of ATF
fluid jets
• Nozzle type/
geometry
• System flow rate
• Jet velocity
• Parasitic power
2. Relative position
between measured heat
transfer and jet location
• Impact of gravity and
free fluid flow
• Fluid interactions
between jets
20
Motor Thermal Management
• Cast aluminum cooling jacket pressed around the stator
• Water-ethylene glycol (WEG) circulated through three cooling channels within the cooling jacket Inlet
Outlet
View of the cooling channels showing the WEG flow path
Coolant
Channels
(Cre
dit: K
evin
Bennio
n,
NR
EL)
21
Motor Thermal Management
Use computational fluid dynamics and finite element
analysis
• Validate the models using experimental results
22
Electric Motor Thermal Management
End winding – side 1
End winding – side 2
Stator – middle
solid lines – experiment
symbols – model
23
Electric Motor Thermal Management
Lpm: liters per minute
24
Conclusion Relevance
• Supports transition to more electric-drive vehicles with higher continuous power requirements.
Approach/Strategy
• Engage in collaborations with motor design experts within industry, national laboratories, and universities.
• Perform in-house thermal characterization of materials, interface thermal properties, and cooling techniques.
Summary
• Published results for lamination stack thermal tests.
• Published results for ATF convective heat transfer measurements.
• Built experimental apparatus to measure variation in local convective heat transfer coefficients.
• Developed design and initiated construction of test equipment and sensors to map large-scale convective heat transfer coefficients on motor end-windings with ATF direct cooling.
25
For more information, contact:
Kevin Bennion
Phone: (303) 275-4447
Section Supervisor
Sreekant Narumanchi
Phone: (303) 275-4062
Acknowledgments:
Susan Rogers and Steven Boyd,
U.S. Department of Energy
Tim Burress and Andy Wereszczak
of Oak Ridge National Laboratory
Jana R. Jeffers, previously of NREL
The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges
that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or
reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.
