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Evaluation of Electromagnetic Forces on three-phase Core-Type Power Transformer Windings during Inrush Current by FEM

Eslami, Ali | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39779 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Vakilian, Mehdi
  7. Abstract:
  8. Inrush Current is a form of over-current that occurs during energization of a transformer. For power transformers, the magnitude of the first peak of inrush current is initially several times the rated load current but slowly decreases until it finally reaches the normal exciting current value. This process typically takes several minutes. Time-variant axial and radial electromagnetic forces under inrush current and short-circuit current are calculated (by finite element method; FEM), and compared. An analytic method is presented for computation of inrush current in transformer. The simulation results obtained by this proposed method are compared with the measured values. A compact three-phase, core-type 132/20 kV, 30 MVA, power transformer is modeled, employing two-dimensional (2-D) FEM, the different forces under short-circuit and inrush current conditions are evaluated as a function of time. The simulation results for this sample transformer show that the inrush current axial force is larger than clamping force (which is equal to the net downward axial force that is exerted on the windings during the steady state short circuit condition) even 2.5 seconds after energizing the transformer. Since the inrush current lasts longer, and normally occur more frequent than a short circuit in a power transformer (while, at present, it is not covered by the standard tests or transformer design procedures) it can be a serious threat to damage of transformer windings
  9. Keywords:
  10. Finite Element Method ; Inrush Current ; Power Transformer ; Short Circuit Current ; Electromagnetic Force

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