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Partial Discharge, Heat Transfer, and Windings Mechanical Strength against Short-Circuit Forces Assessment for a 63/20 kV, 30 MVA VPDT Sub-transmission Transformer

Kazemiun, Mahdi | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57489 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Vakilian, Mehdi
  7. Abstract:
  8. Dry-type transformers, specially under subtransmission voltage level, have gained a great importance and popularity in electrical energy systems infrastructure. This is due to their superior environmentally-friendliness, safety and reliability. However, the design process of a dry-type transformer often introduces serious challenges in terms of ensuring the compliance of a design with partial discharge requirements, lightning wave withstand ability and thermal obligations. These challenges which are stemmed from poor dielectric strength and heat transfer ability of ambient air compared to oil, have limited the production of dry-type transformers in sub-transmission voltage class. The current research developed the necessary analytical approaches that enable the design engineers to study steady-state and transient electric fields distributions, short-circuit-induced forces, and temperature-rise of a sub-transmission dry-type transformer, without utilizing time-consuming finite element simulation. The implementation of such approaches can pave for the automation of the design process of sub-transmission dry-type transformers. All of the formulae and methods developed and implemented in this work are validated and assessed using finite element simulations to ensure their accuracy. Three models have been developed. The first model, follows a numerical approach based on interpolation and is able to calculate the maximum electric field intensity in an arbitrary sub-transmission dry-type transformer design. The second model, is a high frequency model for a dry-type transformer that can be used for calculation of voltage distribution throughout the winding after a lightning incident. The final model, is employed to develop an algorithm that can be used to calculate the short-circuit-induced forces in a transformer. All these three models can be used to eliminate the need for finite element simulation in different stages of dry-type transformer design
  9. Keywords:
  10. Subtransmission Transformer ; Partial Discharge ; Finite Element Simulation ; High Frequency Transformers ; Short Circuit Forces ; Roth's Theorem ; Lightning Voltage Distribution

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