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Toroidal Transformer Life Estimation Under Non-Sinusoidal Supply

Saket, Mohammad Ali | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 42971 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Oraee Mirzamani, Hashem
  7. Abstract:
  8. Due to increase in nonlinear loads in today’s applications, the percent of harmonic content has been increased. Transformers are one of the electrical system components that are subjected to these harmonics. The failure of such equipment is an important consideration. Such failure is because of the hotspot temperature rises over the normal temperature withstanding of internal insulation. The increments of hotspot temperature can decrease the transformer insulation life. Totally, because of the presence of many parameters, precise investigation of loss of life is very difficult. Hence, the only meaning of loss of life in this project is the loss of insulation life under heat stresses. Harmonics and overloading will increase the losses of transformers and these losses will increase the hotspot temperature. Therefore, the calculation of losses under different conditions is very important. Toroidal transformers are extending in small power applications, but there is not a unified investigation about thermal behavior and life of them under harmonic and overload conditions. In the first chapter of this thesis, construction and features of toroidal transformers have been described. In the chapter two, basics of harmonic theory and transformer’s losses under harmonic situation have been investigated. In the third chapter, Finite element model of the used toroidal transformer has been simulated using MAXWELL software and losses under different harmonic situations have been calculated. At the last of this chapter, these different harmonic situations have been approximated by overload situations for experimental tests (because there was no access to harmonic generator). In the forth chapter, a thermal lumped parameter model for toroidal transformer has been proposed and this model is verified by thermal finite element results and experimental tests. From this model, hotspot of transformer has been identified and thermal sensors placed in those places. At the last chapter, accelerated aging tests have been performed for 8 toroidal transformers for discovering the relation between lives of transformer and their Hot spot temperatures. Some circuits have been built for more accurate results of experiments. At the last of the chapter, the results of experiments implemented in one AVR micro controller board. This board is not limited to toroidal transformers and has very user friend menu. User can enter his transformer’s insulation data and this circuit can predict life of transformer according to its real time hot spot temperature (which comes from sensors) and the data which user enters to it.

  9. Keywords:
  10. Toroid Transformers ; Life Time Estmation ; Hot Spot ; Harmonic Analysis

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