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Thermo-mechanical Fatigue of Electrical Insulation System in Electrical machine
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
2017 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Termomekanisk utmattning av elektriska isolationssystem i elektriska maskiner (Swedish)
Abstract [en]

Electrical machines in electrified heavy-duty vehicles are subjected to dynamic temperature loadings during normal operation due to the different driving conditions. The Electrical Insulation System (EIS) in a stator winding is aged as an effect of these dynamic thermal loads. The thermal loads are usually high constant temperatures and thermal cycling. The high average constant thermal load is well-known in the electrical machine industry but little is known about the effect of temperature cycling. In this project, the ageing of the EIS in stator windings due to temperature cycling is examined.

In this project, computational simulations of different simplified models that represent the electrical insulation system are made to analyse the thermo-mechanical stresses that is induced due to thermal cycling. Furthermore, a test object was designed and simulated to replicate the stress levels obtained from the simulations. The test object is to ease the physical testing of electrical insulation system. Testing a complete stator takes time and has the disadvantage of having a high mass, therefore a test object is designed and a test method is provided. The results from the finite element analysis indicate that the mechanical stresses induced will affect the lifetime of the electrical insulation system.

A sensitivity study of several thermal cycling parameters was performed, the stator core length, the cycle rate and the temperature cycle amplitude. The results obtained indicate that the stator core length is too short to have a significant effect on the thermo-mechanical stresses induced. The results of the sensitivity study of the temperature cycle rate and the temperature cycle amplitude showed that these parameters increase the thermo-mechanical stresses induced.

The results from the simulations of the test object is similar to the results from the simulations of the stator windings, which means that the tests object is valid for testing. The test method that is most appropriate is the power cycling test method, because it replicates the actual application of stator windings. The thermally induced stresses exposing the slot insulation exceeds the yield strength of the material, therefore plastic deformation may occur only after one thermal cycle. The other components in the stator are exposed to stresses below the yield strength.

The thermally induced stresses exposing the slot insulation are high enough to low cycle fatigue the electrical insulation system, thus thermo-mechanical fatigue is an ageing factor of the electrical insulation system.

Place, publisher, year, edition, pages
2017. , p. 72
Series
Karlstad University Studies, ISSN 1403-8099 ; 1
Keywords [en]
Thermal mechanical fatigue, Thermo-mechanical stress, electrical machine windings, electrical insulation system, slot insulation, slot liner, groundwall insulation, conductor insulation, turn insulation, stator
National Category
Materials Engineering Mechanical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-62579OAI: oai:DiVA.org:kau-62579DiVA, id: diva2:1129677
External cooperation
Scania CV AB
Subject / course
Materials Engineering, Master of Science
Educational program
Engineering: Mechanical Engineering, spec. in Materials Engineering (300 ECTS credits)
Presentation
2017-06-09, 21A 342 (Eva Eriksson salen), Universitetsgatan 2, Karlstad, 21:13 (English)
Supervisors
Examiners
Available from: 2017-08-25 Created: 2017-08-05 Last updated: 2017-08-25Bibliographically approved

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Ahmed Elschich, Master thesis, Msc in mechanical engineering(4925 kB)867 downloads
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