Minimized Field Enhancement Cylindrical Air-Core High-Voltage Pulse Transformer

An air-core strip-type high-voltage pulse transformer (HVPT) features a relatively simple structure in terms of design and fabrication. However, this HVPT requires considerable attention to prevent dielectric breakdown between the conductor windings. Because each spiral winding must be very thin, the field enhancement at the edges of the windings is very high. Therefore, it is important to develop proper methods to reduce the field enhancement factor and to prevent the dielectric breakdown at the winding edges. In this paper, in order to minimize the field enhancement, the proposed HVPT winding edges were folded, and each winding width was designed to decrease gradually to form a reverse trapezoid. These windings were insulated by multilayer insulators arranged in a specific manner. The requirement specifications are a maximum input voltage of 50 kV and an output voltage of 400 kV. This paper describes a design process and an electric field analysis to reduce the field enhancement. The simulation and experimental results confirmed the validity of the fabricated HVPT. The dielectric breakdown strength was tested up to 467 kV.