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"A Combined "A Combined "A Combined "A Combined A Combined A Combined ElectromagneticElectromagnetic--CFD CFD Thermal Simulation Thermal Simulation
A Combined A Combined ElectromagneticElectromagnetic--CFD CFD Thermal Simulation Thermal Simulation for Power for Power Transformers"Transformers"for Power for Power Transformers"Transformers"
Mark Mark ChristiniChristiniMark Mark ChristiniChristiniXiao Xiao HuHuXiao Xiao HuHu
© 2010 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary
Outline
Introduction
Magnetic Simulation using Maxwell 3D
Thermal Simulationusing Fluentusing Fluent
Summary
Future Work
© 2010 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary
Introduction
• Power transformers are oil-filled to provide insulation as well as an effectiveprovide insulation as well as an effective cooling mechanism.
• Power transformer windings are very complicated and consist of hundreds ofcomplicated and consist of hundreds of copper conductors surrounded by pressboard insulating collars and flanges which direct the flow of oilwhich direct the flow of oil.
• Eddy losses in the copper conductors due to skin and proximity effects will vary based on their location in the windingbased on their location in the winding.
• This magnetic-thermal system creates an extremely difficult electromagnetic-CFD thermal problem
© 2010 ANSYS, Inc. All rights reserved. 3 ANSYS, Inc. Proprietary
thermal problem.
Introduction Oil Filled Transformer Coolingg
OA rating - external FA/FOA rating – forced air/oil
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radiators for natural cooling only
FA/FOA rating forced air/oil using fans/pumps to go through external radiators
Introduction Fluid Flow in Oil Filled Transformer
C t f t i l 3 h Oil-flow though winding
© 2010 ANSYS, Inc. All rights reserved. 5 ANSYS, Inc. Proprietary
Cut-away of typical 3ph oil-filled power transformer
Oil-flow though windinghaving LV layers and HV disks
Electromechanical Design Flow
SimplorerSystem Design RMxprt
Motor Design
Q3DParasitics
PP := 6
ICA:
A
A
A
GAIN
A
A
A
GAIN
A
JPMSYNCIA
IB
IC
Torque JPMSYNCIA
IB
IC
TorqueD2D
Motor Design
PExprtANSYS CFD
Fluid Flowp t
Magnetics
Maxwell 2D/3DElectromagnetic Components
ANSYS MechanicalThermal/Stress
Model order Reduction
© 2010 ANSYS, Inc. All rights reserved. 6 ANSYS, Inc. Proprietary
Co-simulation
Field Solution
Model Generation
Electromechanical Design Flow
Simulation Steps:1. Create and Solve the Eddy Current Transformer1. Create and Solve the Eddy Current Transformer
Model in Maxwell. 2. Export Geometry File from Maxwell.3. Read Geometry File and Create Mesh for Fluent.4. Map Ohmic Losses from Maxwell Using Built-in
capability in Fluent R13capability in Fluent R13. 5. Solve Fluent Model.
© 2010 ANSYS, Inc. All rights reserved. 7 ANSYS, Inc. Proprietary
Transformer Example
• 1ph oil-filled power transformerMagnetic core in center• Magnetic core in center
• High voltage disk winding on outside
• LV layer winding on inside• Insulation tubes, plates and
spacers direct oil-flow• Cooling is OA (oil-to-air only)
with external radiators assumed
(Note: since radiators are not explicitly modeled, heat transfer coefficients on tank walls are
© 2010 ANSYS, Inc. All rights reserved. 8 ANSYS, Inc. Proprietary
increased to represent the radiators)
Magnetic Simulation
• Maxwell 3D Eddy Current solver used
• Frequency = 60Hz sinusoidal
• Linear coreLinear core permeability = 300 with zero conductivity since laminated steel
• Skin and proximity effects considered in LV layer winding onlyy g y
• Model reduced to ¼ symmetry
• Insulation pieces
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Insulation pieces included in order to export directly to Fluent
Transformer Geometry and Magnetic Meshg
• complicated insulation structure
winding tubes
• mesh = 435,000 tets
main HV-LV
ins lationinsulation
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Core, clamp, and tie plate mesh
Winding and insulation mesh
disk key spacers layer vertical
spacers
Maxwell Statistics
• RAM Usage : 8GB
• Solve Time : 1.5hour using 8 processorsp
• Number of elements :elements : 435,000 tets
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Magnetic Field Plot
• Indicates high ti fi ldmagnetic field
between HV and LV windings forwindings for loaded case
• Will cause significantsignificant proximity losses in LV layer windinglayer winding
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Current Density Plot
• Indicates high current density atcurrent density at ends of LV foil windings where fringing flux cuts g gthe layers
• HV disks solved asHV disks solved as stranded so uniform loss densityy
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Loss Density Plot in Windings
• Spatial loss density (W/m3) is directly(W/m ) is directly imported into Fluent
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Summary of Losses
• Spatial loss imported directly from Maxwell– HV winding = 6,252 W– LV winding = 26,438 W
Top clamp
Right tieplate
• Additional loss assigned in Fluent
Right tieplate
Core
HV indingassigned in Fluent– Core loss = 10,000 W– Top clamp = 1,000 W
Bottom clamp = 1 000 W
HV winding
LV winding
– Bottom clamp = 1,000 W– Left tieplate = 500 W– Right tieplate = 1,000 W
Left tieplate
Bottom Clamp
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Export Winding Loss from Maxwell
• Spatial loss exported to link file using menu inside of Maxwell 3D
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Import Winding Loss into Fluent
Ohmic loss distribution in Maxwell Ohmic loss distribution in Fluent
Total amount of loss
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Total amount of loss matches exactly that from Maxwell (32690 w)
Transformer Geometry and CFD Mesh
Copper mesh Insulator mesh
• Cell count : 12 M• Element : Hex in
most regions
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most regions• Conformal fluid solid
mesh Fluid meshSteel core mesh
Fluent Statistics
• RAM Usage : A rule of thumb is that 1G memory is needed for 1M computational fluid cells running single precision. The case has 5 5M computational fluid cells and 6 5M computational solid cells5.5M computational fluid cells and 6.5M computational solid cells. And it needs approximately 8G memory running single precision. Running double precision, which is typical, would need 16G memory.
• Solve Time : on 16 CPUs, it takes approximately 24 hours to finish 3000 iterations. Depending on the setup, such a case takes a few th d t t th d it ti tthousand to ten thousand iterations to converge.
• Number of Unknowns : It solves seven equations for each computational fluid cell and it solves one equation for eachcomputational fluid cell, and it solves one equation for each computational solid cell. Thus, the total number of unknowns is approximately 45M.
© 2010 ANSYS, Inc. All rights reserved. 19 ANSYS, Inc. Proprietary
LV Layer WindingVelocity Vector DistributionyFluid flow at top of layer windings directed by insulation layers and top winding plate
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Temperature Distribution
Temperature distribution shows absolute temperature (in Kelvin)
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Summary
• Using Maxwell 3D and Fluent, an oil-filled power transformer was simulated to determine flow pattern and temperature distribution inside the transformer.
• This information can help designers visualize the flow and• This information can help designers visualize the flow and temperature inside the transformer and thus help design better cooling system for the transformer.
© 2010 ANSYS, Inc. All rights reserved. 22 ANSYS, Inc. Proprietary
Future Work
• Increase complexity of winding conductors/stranding so that AC losses in HV disk winding can be considered
• Increase complexity of insulation structure by adding baffles and an outer winding tube on HV disk winding tobaffles and an outer winding tube on HV disk winding to observe zig-zag oil flow through windings
© 2010 ANSYS, Inc. All rights reserved. 23 ANSYS, Inc. Proprietary
Appendix : Fluent Setup
• Solver : steady state• Viscous model : laminar (can use turbulence model based on Ra
d P b )and Pr number)• Natural convection model : Boussinesq model• Boundary conditions : symmetry and wall with heat transfer
coefficientcoefficient• Pressure velocity coupling scheme : SIMPLE• Pressure spatial discretization : PRESTO!• URFs : 0 1 for momentum and 0 2 for pressure• URFs : 0.1 for momentum and 0.2 for pressure
Fluent Tutorial 5, Modeling Radiation and Natural Convection, gives all the details on how to set up a natural convection problem in Fluent.
The test case is also available upon request.
© 2010 ANSYS, Inc. All rights reserved. 24 ANSYS, Inc. Proprietary
The test case is also available upon request.