fem modeling of transformer
TRANSCRIPT
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POWER TRANSFORMER FAILURE AND CHALLENGES IN THE TRANSFORMER DESIGN
Matthias Bucher, PhD
Computational and Applied Electromagnetics GroupInstitute for Energy TechnologyUniversity of Applied Sciences, Rapperswil, Switzerland
Infolytica Engage User Conference, October 27, 2015
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Agenda
Research and development at CAEM group
Power and drive transformers
Challenges in the transformer design
Application of Infolyticas MagNet and ElecNet Equivalent HF-circuit FEM-modeling Extraction of inductances and capacitances Transient time-domain solution Comparison with measurements Visualization
Conclusions and Outlook
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Research and Development at CAEM Group
Electromagnetic field simulations at low and high frequency
Virtual prototyping and product development
Electromagnetic analysis and design optimization
Power and drive transformers, MV and HV switchgear, electric motors
Measurement and testing at our high-voltage lab 800kV lighting pulse tests 150kV AC, +/- 270kV DC Partial discharges
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Power Transformers
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Source: Swissgrid
Source: ABBSource: ABB
Source: ABB
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Drive Transformers
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Source: ABB
M~~~
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FrequencyConverter Motor
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Challenges in the Transformer Design
Transient overvoltages due to
Lightning strikes
Switching operations in circuit breakers
Ferro-resonances
can cause a non-linear voltage distribution over the transformer windings, high field strengths between turns, and eventually lead to destruction of the winding insulation.
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Sou
rce:
EE
P
HV LV
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Challenges in the Transformer Design
Solution: computation of the transient voltage distribution over the transformer winding to find hot spots and to improve the dielectric design of the transformer.
Needed: equivalent electric HF-circuit of the transformer to compute turn voltages
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Equivalent HF-circuit
Equivalent electric circuit of 4 turns
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FEM Modeling of Transformer
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rotation axisPrimary (HV)Secondary (LV)Core
3D 2D axis symmetric
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FEM Modeling of Transformer
Modeling in MagNet
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meshing
HVLV
core
HV turns modeled as individual coils
LV foils modeled as block (2x) LV-coils are short-circuited
M5 core steelEP04 epoxyAluminium
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FEM Modeling of Transformer
Modeling in ElecNet
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Core is grounded HV turns modeled as individual
electrodes LV foils modeled as block (one
single electrode)
M5 core steelEP04 epoxyAluminium
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Extraction of Winding Inductances
Extraction of turn inductances and magnetic couplings in MagNet1. Initialization of current in coil#1 to 1, all other turns to 02. Time-harmonic 2D simulation3. Calculation of self and mutual inductances of the transformer turns based
on flux linkage: =
4. Flux linkage column vector = first column of inductance matrix
5. Repeat for the next coil
Procedure is automatically repeated for all coils,
which results in a symmetric inductance matrix
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Extraction of Winding Capacitances
Extraction of turn capacitances and electric couplings in ElecNet1. Initialization of current in electrode#1 to 1, all other turns to 02. Time-harmonic 2D simulation3. Calculation of self and mutual capacitance of the transformer turns based
on charges: =
4. Charge column vector = first column of capacitance matrix
5. Repeat for the next electrode
Procedure is automatically repeated for all electrodes,
which results in a symmetric capacitance matrix
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Matrices
C-matrix (left) and L-matrix (left) in logarithmic scale:
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Transient Time-Domain Solution
Equivalent electric
circuit of 4 turns:
Ordinary differential equation:
EMTP-like
trapezoidal
Integration:
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L: inductance matrixC: capacitance matrixR: resistance matrix (winding losses)G: conductance matrix (losses in dielectric)T: incidence matrixx(t): branch currents and node voltagesu(t): source voltage
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Transient Time-Domain Solution
Input surge voltages:
Very fast transient voltage waveform (VFT surge):
Standard lightning impulse (BIL surge):
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Comparison with Measurements
Measurement of turn voltages of a transformer in the lab
Surge generator connected to first turn
Comparison of simulation
results with measurements:
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Visualization of Results (Video)
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Voltage distribution Electric field
Turn
vol
tage
[p.u
.]
Turn number
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Conclusions and Outlook
Accurate tool for lightning strike and switching surge analysis of transformer windings
Accurate computation of winding inductances and capacitances using Infolyticas MagNet and ElecNet
Visualization of the results based on transient simulations in ElecNet
Future improvements: Inclusion of frequency-dependency of winding inductances and resistances Optimization of read-out routine in MagNet and ElecNet to speed up the
simulations
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Thank you for your attention!
Power transformer failure and challenges in the transformer design AgendaResearch and Development at CAEM Group Power TransformersDrive TransformersChallenges in the Transformer DesignChallenges in the Transformer DesignEquivalent HF-circuitFEM Modeling of TransformerFEM Modeling of TransformerFEM Modeling of TransformerExtraction of Winding InductancesExtraction of Winding CapacitancesMatricesTransient Time-Domain SolutionTransient Time-Domain SolutionComparison with MeasurementsVisualization of Results (Video)Conclusions and OutlookFoliennummer 20