Design and Development of High-voltage and High-frequency Transformer for Solid-state Transformer* Park Siho School of Architectural, Civil, Environmental, and Energy Engineering 

Graduate School, Kyungpook National University Daegu, Korea
 (Supervised by Professor Cha Honnyong)

 (Abstract)
In this paper, design guide of high-voltage isolated high-frequency transformer is proposed. Since a potential difference of up to 20 kV occurs at both ends of a transformer constituting a 3-port 3-level NPC based dual half-bridge DAB converter of solid-state transformer, it is necessary to design a transformer capable of 30 kV insulation considering margin. In order to insulate a voltage of 30 kV with air only, a very long distance between the primary and secondary wire of the transformer must be used. Therefore, bobbins made of Teflon resin and Polycarbonate were fabricated and insulation was obtained. To reduce the insulation parameter, core was connected to output neutral point terminal. The bobbin consists of an inner bobbin, an outer bobbin, a guard, and is designed to have sufficient dielectric strength. Through the simulation verification, only the primary wire portion was molded to remove the dielectric breakdown element generated at the portion where the outer bobbin and the guard contact with each other. A prototype transformer was built, completed operation verification and passed 30kV withstand voltage test. In the case of temperature test, there is no enough air layer to allow heat to escape from the secondary wire. Therefore, a high number of temperatures are measured, but this can be solved by turning the fan on.