Dan Barber - Lord Corporation

Optimizing Thermal Management in E-Motors
Daniel E. Barber, Ph.D.
Staff Scientist, Electronic Materials Technology
©2018 LORD Corporation

2 | ©2018 LORD Corporation
• Introduction to LORD Corporation
• High Thermal Conductivity (“High TC”) Material Options
• Thermal & Power Density Benefits of Motor Potting
– Performance & Accelerated Aging Studies at LORD
– Customer Case Studies
• Guidelines for Motor Potting – Material Choice & Potting Recommendations
• Other Advantages of Potting for Thermal Management in E-Motors
Outline

LORD Corporation – Introduction
• A diversified technology and manufacturing company
• More than 90 years old, privately-held
• 3,100 employees in 26 countries
• Cary, NC (Raleigh-Durham area) global headquarters
• 19 manufacturing facilities and 10 R&D centers worldwide
Key Markets
• Automotive
• Energy
• Electronics
• Marine
• Industrial
• Aerospace & Defense
• Oil & Gas
Key Products
• Thermal Management /
Electronic Materials
• Adhesives & Coatings
• Sensing Systems
• Electro-Mechanical Motion
& Vibration Control Systems
• Motion & Vibration Control
Assemblies Visit us online at LORD.com/CoolTherm

Different Material Forms for Different Applications
Potting Materials
• Low viscosity
• Self-leveling
• Rigid or soft
• Thermal management and
protection from the environment
Adhesives Gap Fillers
Dispense as bead or
viscous liquid
Dispense as bead
Cure to rigid or flexible solid Cure to soft solid
High bond strength Low adhesion

Different Material Types Have Different Strengths & Weaknesses
• Thermal benefit in E-Motors
is about the same regardless
of material chemistry
• Temperature stability & other
considerations make Epoxy
(and to a lesser extent,
Silicone) preferable.
• More about this later…

Electric Motor Potting Studies

Electric Motor Studies: Prior Work
Oil-cooled stator design
from S. Nategh et al., 2013
Current/power at maximum temperature was
‒ 14% higher with Epoxylite
‒ 26% higher with LORD SC-320.
SC-320
Epoxylite
Varnish
40
60
80
100
120
140
160
180
3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6
EndWindingTemperature(C)
Current(A)
error bars = 3 StDev
MotorTemperatureLimit
Average Winding Temperature vs. Current

• Higher power density
– More torque/horsepower from a similarly-sized motor
– Same torque/horsepower from a smaller motor
• Better reliability
– Low-temperature operation means insulation will not degrade as quickly
– Lifetime doubles for every 10°C decrease in temperature
• Lower copper losses at lower temperature
– Less resistance to current flow = lower I2R losses
Expected Benefits of Improved Thermal Performance

• Class F, NEMA Premium, 3 HP, TEFC, 1760 RPM
• Voltage: 208-230/460, three-phase, 60 Hz
• Full load current: 8.4-7.8/ 3.0
• Three potting conditions:
– As-received (with varnish)
– 3.2 W/m∙K silicone (CoolTherm™ SC-320)
– 1.4 W/m∙K epoxy-potted (competitor)
LORD Motor Potting Study: Motor Details
In cooperation with Advanced MotorTech, http://advancedmotortech.com/

Insert
Housing
• Paint LORD P-1292 primer
• Mix LORD SC-320 resin & hardener
• Pot end turn with SC-320
LORD Motor Potting Study: CoolTherm™ SC-320 Potting Process
• Apply vacuum and
get bubbles out
• Cure 24 hours at
room temperature • Remove insert
& clean air gap
10 | © 2014 LORD Corporation

Heat test was run to constant temperature
(about 3 hours in each case) at the
following output loads:
Speed
(rpm)
Torque
(N∙m)
% Rated
Torque
Output power
(HP)
% Rated
Power
1759 12.4 100% 3.1 102%
1717 20.2 163% 4.9 163%
1703 21.5 174% 5.2 172%
LORD Motor Potting Study: Motor Test Procedure

SC-320 vs. varnish-only motor:
• Temperature more than 30oC lower
at the same torque/HP
• Torque/HP up to 16% higher at the
same temperature
• Copper losses up to 10% lower
• Benefits are more pronounced at
higher torque/HP
LORD Motor Potting Study: Motor Test Results
% Rated
Torque
% improvement in
copper loss
100% 2.7%
163% 6.6%
174% 10.2%

• Coil temperatures from simulation match test data well.
• Rotor temperature is predicted to be about 10°C cooler with SC-320 potting
LORD Motor Potting Study: Thermal Simulation Results
Varnish only CoolTherm™ SC-320 1.4 W/m∙K epoxy
H. Li et al., IEEE, Tran. Ind. Appl. Vol. 53, No. 2, pp. 1063–1069, March-April 2017.

• Many motor manufacturers require a
more rigid potting material, with good
chemical resistance.
• Study was repeated using epoxy
potting materials with different
thermal conductivity.
• Similar thermal performance was
observed.
– CoolTherm™ EP-3500 (3.5 W/m∙K)
had comparable performance to
CoolTherm™ SC-320 (3.2 W/m∙K)
LORD Motor Potting Study: High TC Epoxy Results

• Motors were run at high load under rapid start-stop conditions.
• Motors were run for 8 hours/day, then cooled to room temperature overnight
(25 days of temperature cycling).
• All motors were run to failure by increasing target temperature weekly.
LORD Motor Potting Study: Accelerated Aging Test Procedure
Average daily temperatures were
determined from this region
Reference
Unpotted
High TC
Time (hours)
Temperature(°C)

LORD Motor Potting Study: Accelerated Aging Test Results
• End winding temperatures were up to
45°C cooler than unpotted motor
• Highly-filled, high-TC epoxy resisted
cracking during thermal cycling.
CoolTherm™ EP-3500 Competitor 1.2W/m∙K epoxy
Test Day
Temperature(°C)
Average End Winding Temperature by Day
Unpotted
CoolTherm™ EP-3500

• Siemens 1LE1041-1AA63-4 motor: three-phase, squirrel cage rotor, 4 kW (5.4 HP), Class F, self-
ventilated surface-cooled, no varnish.
• Four stators potted with two epoxy (3.5 W/m∙K) and two silicone (3 W/m∙K and 4 W/m∙K) materials.
• Electrical tests at rated power and at overload (~140°C).
• Thermal cycling (150 cycles, 2.5h at -60°C then 2.5h at 200°C)
• Repeat electrical tests as above.
Customer Case Study #1: Siemens AG – Test Plan
Teflon insert
Bottom
Top
Potted with CoolTherm EP-3500
(3.5 W/m∙K epoxy)
Stator with insert,
ready for potting
Stock motor

Before thermal cycling:
•25-35°C cooler at 4 kW (rated power)
•16-21% more power at thermal limit
Case Study #1: Results
After thermal cycling:
•EP-3500 epoxy performance unchanged
•Others: 15-20% more power
– No data on unpotted motor after cycling

Epoxy:
• No large stress cracks or separation from housing
• Hairline stress cracks in inner diameter
Case Study #1: Potted Motors Post-Test
EP-3500 (top) Epoxy Prototype 2 (bottom) SC-320 (3W silicone) SC-324 (4W silicone)
Silicone:
• Some separation from housing, but not severe
• Some material abrasion due to thermal expansion

Application:
– High power density motor, press-fit housing
– Used in enclosed space – minimal convection
for cooling
Test motor configurations
– No potting, no paint (control)
– Thermally emissive paint on housing
– Potted with CoolTherm™ SC-320 silicone, with
thermally emissive paint on housing
Customer Case Study #2
– Paint only: 16% more power at 7°C cooler temperature
– Paint & potting: 30% more power at 9°C cooler temperature

• Temperatures 30-50°C lower and output power 15-30% higher are typical
with high TC materials (epoxy or silicone)
– Efficient heat sink (liquid jacket, emissive paint) will give better results
– Thermal benefit increases as power output & temperature increases
• Cracks in potting material do not necessarily degrade performance, unless:
– Material separates from the housing (delamination)
– Cracks allow ingress of damaging chemicals or moisture
• Lower copper losses are observed
– Efficiency may not be substantially improved if other losses dominate (bearing, magnetic, etc.)
• Rotor cooling may be possible
– Unless air flow through the stator end windings is used for rotor cooling
Lessons Learned from Stator Potting Studies & Customer Feedback

Early in the design process, engage a
material supplier with expertise in multiple
types (silicones and epoxies, especially)
Guidelines for Choosing the Right Potting Material
Epoxy
– Rigid, good adhesion, low thermal expansion
– Best chemical resistance
– High-temperature versions available, but varies
Silicone
– Highest temperature range (-60 to >200°C)
– Soft, low stress, but high thermal expansion
– Low adhesive strength, poor chemical
resistance

• Ensure good contact with heat sink (good adhesion and adequate surface area)
• Potting under vacuum is generally recommended to ensure complete fill of fine
gaps
• Fill from the top is an easier process but requires adequate flow path from top to
bottom
– Bottom fill process is preferred if the only flow path is through a tightly-packed slot
• Take into account thermal expansion when designing the mold
– Design mold pieces for the potting temperature
– Consider thermal expansion of potting material during operation
General Considerations for Potting Motors

General Considerations for Potting Motors
Easy Not so easy

• Ruggedization– Potted windings are less susceptible to vibration and better
protected from environmental contamination, especially with epoxies.
• More even temperature distribution throughout the windings– Less likelihood of
“hot spots” where failures & shorts can occur.
• Lower flammability/ More explosion-proof– Potting material displaces air, so
overall flame & explosion risk is lower.
• No cooling oil build-up in windings– ATF in direct oil-cooled motors can “gunk up”
windings, limiting thermal transfer and degrading wire insulation.
Other Potential Advantages of Potting versus Air or Oil Cooling

• Thermal management materials help
extend lifetime and increase power density.
• Collaborative design helps to take
maximum advantage of the properties of
high TC potting materials.
– How much thermal conductivity is needed?
– What type of material is required?
– How can it best be applied in your devices?
• Engage with your material supplier early in
the design process for best outcomes.
Summary

Motor Potting Studies:
– S. Nategh, A. Krings, O. Wallmark, “Evaluation of Impregnation Materials for Thermal Management of Liquid-Cooled
Electric Machines,” IEEE, Tran. Ind. Electron. Vol. 61, No.11, pp. 5956-5965, November 2014.
• “Thermal Analysis and Management of High-Performance Electrical Machines,” S. Nategh doctoral dissertation,
http://kth.diva-portal.org/smash/get/diva2:623376/FULLTEXT01
– H. Li, K. W. Klontz, V. E. Ferrell, D. E. Barber, “Thermal Models and Electrical Machine Performance Improvement
Using Encapsulation Material,” IEEE, Tran. Ind. Appl. Vol. 53, No. 2, pp. 1063 – 1069, March-April 2017.
– M. Rovito, “Engines of Fate,” Charged, pp. 26-29, June-July 2014.
• Related LORD white paper at http://lordfulfillment.com/pdf/44/LL3243_MotorPowerDensity.pdf
– C. Ruoff, “Motor Potting Potential,” Charged, pp. 20-25, September-October 2016.
• Related LORD white paper at http://lordfulfillment.com/pdf/44/LL3246_PottedMotors.pdf
Inductor Potting Study:
– “Thermally Conductive Potting Compounds Enable Higher Power Density Electronics,” D. Barber and E. Wyman,
LORD White Paper, February 2016, http://lordfulfillment.com/pdf/44/LL3244_Inductor-PottingCompounds-
HigherPowerDensity.pdf
For More Details

Please visit our booth:
Hall 1.1b, Booth 11E59
Thank you for your attention!
Dan Barber
Daniel_Barber@LORD.com
+1.919.342.4497
LORD.com/CoolTherm

• Data gathered on NEMA Premium
Efficiency industrial motors from a
single manufacturer.
• Motor weights calculated with
various motor output power
improvements.
• Volume of potting material calculated
from motor dimensions. Weight
calculated assuming 3 g/cm3 density.
• Needs experimental verification.
SUPPLEMENT - Estimated Weight Reduction with Potted Motors
Sample estimates:
• 20HP motor at 15% power increase: 13 kg savings vs. 113 kg motor
• 40HP motor at 25% HP increase: 48 kg savings vs. 227 kg motor
227
454
680
907
1134
(kg)

Dan Barber - Lord Corporation

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