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Step-Up Asymmetrical Nine Phase Delta-Connected Transformer for HVDC Transmission

  • Ammar, Arafet Ben (Laboratory of Materials, Measurements and Applications, National School of Engineering of Tunis, University of Tunis) ;
  • Ammar, Faouzi Ben (Laboratory of Materials, Measurements and Applications, National Institute of Applied Sciences and Technology, University of Carthage)
  • Received : 2017.03.30
  • Accepted : 2018.04.16
  • Published : 2018.11.20

Abstract

In order to provide a source for nine phases suitable for 18-pulse ac to dc power, this paper proposes a new structure for a step-up asymmetrical delta-connected transformer for converting three-phase ac power to nine-phase ac power. The design allows for symmetry between the nine output voltages to improve the power quality of the supply current and to minimize the THD. The results show that this new structure proves the equality between the output voltages with $40^{\circ}-{\alpha}$ and $40^{\circ}+{\alpha}$ phase shifting and produces symmetrical output currents. This result in the elimination of harmonics in the network current and provides a simulated THD that is equal to 5.12 %. An experimental prototype of the step-up asymmetrical delta-autotransformer is developed in the laboratory and the obtained results give a network current with a THD that is equal to 5.35%. Furthermore, a finite element analysis with a 3D magnetic field model is made based on the dimensions of the 4kVA, 400 V laboratory prototype three-phase with three-limb delta-autotransformer with a six-stacked-core in each limb. The magnetic distribution flux, field intensity and magnetic energy are carried out under open-circuit operation or load-loss.

Keywords

References

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