SLIDE 1
Thermal Analysis & Design Improvement of an Internal Air-Cooled Electric Machine
- Dr. James R. Dorris
Thermal Analysis & Design Improvement of an Internal Air-Cooled - - PowerPoint PPT Presentation
Thermal Analysis & Design Improvement of an Internal Air-Cooled - - PowerPoint PPT Presentation
Thermal Analysis & Design Improvement of an Internal Air-Cooled Electric Machine Dr. James R. Dorris Application Specialist, CD-adapco Thermal Analysis of Electric Machines Motivation Thermal challenges in electric machines Workflow
SLIDE 2
SLIDE 3
The past 10 years shows industry focus on:
– high torque / power density / high efficiency – and reduction in size, weight, cost
This combination leads to more performance from a smaller package – and a thermal challenge.
Motivation: – Electric Machine Industry Focus
Source graphics: NREL
Increased operating temperatures would result in:
– Requirement for better insulating materials – Reduced lifetime due to higher risk of thermal damages to insulations, bearings, etc
Improved cooling systems via CFD thermal simulation provide engineering value.
Source graphics: Integrated Magnetics
– Higher risk of demagnetizing permanent magnets
20 ºC 110 ºC 140 ºC 200 ºC 230 ºC
Demagnetization
SLIDE 4
4
Electromagnetic Analysis: – The SPEED suite of programs
The following machine types are available: PC-BDC: Brushless permanent magnet and wound-field AC synchronous
PC-IMD: Induction PC-SRD: Switched Reluctance PC-DCM: Direct Current (PM) PC-WFC: Wound-field and commutator PM
SLIDE 5
CD-adapco Tools For Electric Machines – SPEED and STAR-CCM+ Workflow
- 2. Stability check with
static and dynamic analytical analysis
- 3. FE-analysis and fitting
- f the analytical model
- 5. If stable results, transfer
- f the heat loss distribution
from the FE-analysis to STAR-CCM+ via the sbd-file
FE-grid SPEED FV-grid STAR-CCM+
- 6. Mapping process for rotor and stator
heat losses is carried out separately and automatically with transfer of the values from neighbor grid node in SPEED to STAR-CCM+
- 1. Create SPEED model
based on geometry, parameters, & winding scheme
Data transfer
- 4. Preparation of the geometry
in STAR-CCM+ by reading the xGDF file
- 7. Solving and post processing
in STAR-CCM+
Electric machine design solution – Template based geometry, analytic tool + models for 3D effects, 2D FEA solver. Multi-physics, general purpose simulation solution General geometry, 3D finite volume solvers
SLIDE 6
Project Description – Induction Motor Thermal Performance
Challenge:
– A North American Motor Company’s (NAMC) internal fan cooled split-phase induction machine is not sufficiently cooled, expensive to test many design configurations.
Solution:
– Develop a steady-state thermal analysis of a machine using the CD- adapco SPEED STAR-CCM+ workflow.
Procedure:
– Compute losses using SPEED – Import SPEED geometry, losses, NAMC CAD for non-active components into STAR-CCM+ – Define appropriate physics, boundary conditions – Solve Conjugate Heat Transfer (CHT) simulation at the specified load point – New load point only requires losses to be re-computed and re-imported into STAR-CCM+ - can be ready in ~15min. – Geometry changes can be performed by swapping out parts and re-meshing – can be ready is less than 1 day.
SLIDE 7
Electromagnetic Analysis – Computing losses using SPEED
2-D Geometry, winding definition Materials
– Lamination Steel, rotor cage
Controller definition, simulation settings Analytic Calculations (< 1s) 2D FEA electromagnetic solution (<1min) Fast computation, can connect with HEEDS optimization engine Heat Loads Losses computed from FEA B-field distribution via Steinmetz Model
SLIDE 8
Physics Modeling
SPEED Geometry:
– Active Components
NAMC Geometry:
– Non-Active Components
Windings modeled as bulk material – I2R loss slot dependent – Anisotropic Thermal Conductivity Rotor Cage I2R Losses
– Uniform distribution over rotor bars
I2R loss Temperature Dependent
– SPEED model losses computed at average temperature – STAR-CCM+ model adjusts for local temperature dependent resistivity
𝜍𝑊 = 𝑅𝑈 ∗ (1 + 0.00393 ∗ 𝑈 − 𝑈
𝑠𝑓𝑔
𝑊 )
Where 𝝇𝑾 is the volumetric heat load, 𝑅𝑈 is the total heat load, 𝑼 is the local region temperature, 𝑼𝒔𝒇𝒈 is the average temperature (80 C) and 𝑾 is the region volume.
End-winding surface roughness Core losses spatially dependent
SLIDE 9
- Rotor Bar Avg=116.7 C, End Ring 1 Avg=114.1 C, End Ring 2 Avg=115.9 C
- Shaft Min Temp=44.8 C, Shaft Max Temp=116.5 C
- SPEED model with rotor temp @ 116 C requires 52.5 % of copper
conductivity for consistent losses and performance at this load point.
Simulation Steady State Temperatures
1 1 2 2
SLIDE 10
Comparison with Measurements
- NAMC Measurements on aux and main winding at 2 circumferential locations,
both for the fan (cold side) and exhaust (hot side) of the end winding.
- Do not resolve aux vs. main winding due to NAMC’s end-winding geometry.
- Compare with mean and standard deviation of temperature in outer 5mm of end-
winding
End Winding 2 (cold side)
Measurement Simulation % Error Mean 70.6 C 71.6 C 1.40 % STD 3.38 C 1.94 C
End Winding 1 (hot side)
Measurement Simulation % Error Mean 88.0 C 88.5 C 0.57 % STD 3.16 C 1.08 C
SLIDE 11
Heat Flow: Rotor and Stator – Easy Reports in STAR-CCM+
Aux + Main Winding Copper Loss 171 W 84 W 87 W Stator Lams Air Iron Loss 82 W Air Housing 49 W 120 W Rotor Cage Copper Loss 102 W 36 W 66 W Rotor Lams Air Iron Loss 17 W Air Shaft 42 W 41 W
Stator: Rotor:
SLIDE 12
CD-adapco Tools For Electric Machines – SPEED and STAR-CCM+ Workflow
- 2. Stability check with
static and dynamic analytical analysis
- 3. FE-analysis and fitting
- f the analytical model
- 5. If stable results, transfer
- f the heat loss distribution
from the FE-analysis to STAR-CCM+ via the sbd-file
FE-grid SPEED FV-grid STAR-CCM+
- 6. Mapping process for rotor and stator
heat losses is carried out separately and automatically with transfer of the values from neighbor grid node in SPEED to STAR-CCM+
- 1. Create SPEED model
based on geometry, parameters, & winding scheme
Data transfer
- 4. Preparation of the geometry
in STAR-CCM+ by reading the xGDF file
- 7. Solving and post processing
in STAR-CCM+
Electric machine design solution – Template based geometry, analytic tool + models for 3D effects, 2D FEA solver. Multi-physics, general purpose simulation solution General geometry, 3D finite volume solvers
Original Design Modified Design
SLIDE 13
- Geometry of Stator swapped
for vented stator design:
Phase 2: Vented Stator – Design Improvement
- Approximately 1 day work
required by intermediate user to swap geometry
- New geometry part created in
STAR-CCM+
- Conformal interfaces rebuilt
- Entire model re-meshed
- Physics / boundary conditions
reset
- Expecting Temperatures to
drop across entire model:
- Lower Copper Temp / Heat load
- Lower Al Cage Temp / Heat load
SLIDE 14
- Rotor Avg=96.7 C
- End Ring 1 Avg=93.7 C
- End Ring 2 Avg=96.6 C
- Shaft Min Temp=36.0 C
- Shaft Max Temp=96.7 C
Simulation Steady State Temperatures
1 1 2 2
- End Winding Temperatures decreased by nearly 20 C.
End Winding 2 (cold side)
Orig Design Vented Stator % Mean 70.6 C 59.2 C 16.1 % STD 3.38 C 2.13 C
End Winding 1 (hot side)
Orig Design Vented Stator % Mean 88.0 C 67.9 C 22.8 % STD 3.16 C 0.97 C
– Vented Stator Design – Original Stator Design (reference)
SLIDE 15
Heat Flow: Rotor and Vented Stator
Aux + Main Winding Copper Loss 156 W 62 W 94 W Stator Lams Air Iron Loss 82 W Air Housing 86 W 90 W Rotor Cage Copper Loss 93 W 33 W 60 W Rotor Lams Air Iron Loss 17 W Air Shaft 42 W 35 W
Stator: Rotor:
15 W 9 W 37 W 20 20º C 20 20º C
SLIDE 16
Loss Mechanisms
– Copper losses, spatially distributed iron losses, friction and windage losses
Heat transfer
– Conduction, Radiation – Convection (natural or forced)
Simulation of fluids moving in and around objects
– Liquids and/or gases
Cooling Systems of particular interest for CFD analysis
SLIDE 17