ampacity simulation of high voltage cables• for ampacity calculations for simple configurations...
TRANSCRIPT
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COMSOL Conference Milan 2012
Eva Pelster
Ampacity simulation of high voltage cables
10.10.2012
Excerpt from the Proceedings of the 2012 COMSOL Conference in Milan
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Content (1) Introduction (2) Comparison of IEC standard calculation method with COMSOL
Mutliphysics (3) Evaluation of a three-conductor high voltage cable configuration (4) Conclusion
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(1) Introduction • Cable ampacity typically depends largely on the cross-section of ist
conductor • Due to cost reduction it is of interest to keep the conductor cross-
section low • Usually semi-empirical methods, including larger safety margins, are
used to determine ampacity • Here COMSOL Multiphysics is used to determine the temperature
distribution
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Content (1) Introduction (2) Comparison of IEC standard calculation method with COMSOL
Mutliphysics (3) Evaluation of a three-conductor high voltage cable configuration (4) Conclusion
10.10.2012 4 Ampacity simulaion of high voltage cables
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(2) Comparison of IEC standard calculation method with COMSOL Mutliphysics
• Comparison of IEC-standard ampacity calculation with COMSOL
Multiphysics simulation for: – single-conductor cable – three bundled single-conductor cable
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(2) Comparison of IEC standard calculation method with COMSOL Mutliphysics
• A single-conductor cable is implemented to evaluate the maximum
allowable current, while keeping the conductor temperature at a defined maximum temperature
• The cable consists of a conductor material as well as different isolating layers and armour
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(2) Comparison of IEC standard calculation method with COMSOL Mutliphysics
• IEC standard ampacity calculation:
– Simple calculation of radial heat conduction – Aim is to limit the conductor temperature to 90°C – The conductor generates heat, depending on the current
according to the suppliers information – The maximum allowable current is determined via a iteration
algorithm – The outer surface is cooled via radiation as well as convective
cooling for which the heat transfer coefficient is estimated by adequate correlations
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(2) Comparison of IEC standard calculation method with COMSOL Mutliphysics
• COMSOL Multiphysics ampacity calculation:
– A equivalent model is defined in COMSOL – The heat source is defined according to the IEC calculation
method – The same cooling parameters on the outer surface are used – An iteration is carried out by using a Global equation iterating
towards the maximum allowed conductor temperature
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(2) Comparison of IEC standard calculation method with COMSOL Mutliphysics
• Single-conductor cable, comparison of temperature distribution and
iterated ampacity
• As expected for a simple radial heat conduction problem the results agree with each other 10.10.2012 9 Ampacity simulaion of high voltage cables
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(2) Comparison of IEC standard calculation method with COMSOL Mutliphysics
• The same procedure is carried out for a bundled geometry of three
single-conductor cables
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(2) Comparison of IEC standard calculation method with COMSOL Mutliphysics
• IEC standard ampacity calculation:
– Simple calculation of radial heat conduction is amended by a factor considering the bundled geometry
– Heat source and cooling is implemented according to the first case • COMSOL Multiphysics ampacity calculation:
– The exact geometry is implemented in COMSOL – Heat source and cooling is implemented according to the first case
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(2) Comparison of IEC standard calculation method with COMSOL Mutliphysics
• Three boundled single-conductor cables, comparison of temperature
distribution and iterated ampacity
• With a still simple but more complex geometry results start to differ
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Content (1) Introduction (2) Comparison of IEC standard calculation method with COMSOL
Mutliphysics (3) Evaluation of a three-conductor high voltage cable configuration (4) Conclusion
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(3) Evaluation of a complex three-conductor geometry • Next COMSOL Multiphysics was used to evaluate a more complex
configuration containing free convection in a cylindrical casing • Those configurations are often used in off shore wind farms to route
the cable in a wind turbine to the generator
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(3) Evaluation of a complex three-conductor geometry • The geometry contains multiple conductors, screen and armour as well
as several isolating matterials • The cable itself runs vertivally through an air-filled metal cylinder • The partly extruded geometry:
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(3) Evaluation of a complex three-conductor geometry • Implementation • Cable:
– 3D Heat Transfer in solids – Heat sources in conductot, armour and screen
• Outer cylinder – 2D-axisymmetric Conjugate Heat Transfer – Free convection resulting from the temperature field – Outer surface is cooled via Radiation and Convective Cooling
boundary • Cable surface and air filled cylinder are linked with an Extrusion
Operator
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(3) Evaluation of a complex three-conductor geometry • Results
– The model was evaluated for different load cases, determining the typical temperatures for different conditions
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Content (1) Introduction (2) Comparison of IEC standard calculation method with COMSOL
Mutliphysics (3) Evaluation of a three-conductor high voltage cable configuration (4) Conclusion
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(4) Conclusion • For ampacity calculations for simple configurations the IEC standard
calculation agrees with the simulation results • With higher complexity of the cable configuration the two methods start
to differ, the standard calculation method contains larger safety margins where the simulation has a better ability in resolving the geometrical relations
• It was shown that a larger configuration containing free convection inside a cylinder could be implemented to further investigate cable designs
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Kontakt: Dr.-Ing. David Wenger
Wenger Engineering GmbH Einsteinstr. 55
89077 Ulm 0731-159 37 500