Modeling and Design of Insulation Structure for High Power Density Medium Voltage High-Frequency Transformers

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Abstract
Medium voltage high-frequency transformer, the key component in a medium voltage solid-state transformer, requires high reliability on its insulation parts. With the increase of power density, the insulation design of the medium voltage high-frequency transformer becomes a big challenge. The transformer needs to ensure both high breakdown strength for short-term fault tolerance and low partial discharge for long-term reliable operation. Therefore, beginning with the electric stress analysis and the anti-corona consideration, a mass-manufacturable insulation structure is proposed in this paper. In the structure, an improved multi-shielding structure with an optimized shield potential design is used to reshape the electric field distribution for higher breakdown strength and lower partial discharge. And an end-winding stress grading method is proposed and modeled for both the structure and the material used. Finally, with the proposed insulation structure, a 100 kW partial discharge free transformer prototype with 75 kV base insulation level is built. It passed all insulation tests. Also, the prototype realizes high power density under a high insulation level, which reaches 11.2 kW/L.
Funding Information
  • Zhejiang Provincial Natural Science Foundation of China (LZ22E070002)
  • National Key Research and Development Program of China (2022YFE0138400)

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