We develop a cast resin transformer which has a good heat conductivity due to the geometrics. The electrical isolation of the high voltage winding is done with epoxy cast resin with high voltage resistance, low polarisation and a potting in vacuum without bubbles. An additional acoustic isolation reduces hum noises.
Due to the vector group Yz5 we get a good coupling of the phases and the core legs. The transformer can cope well with unbalanced loads due to this.
By using special transformer metal sheets with a round cross section and low losses we manage very low standby and partial load losses. The tappings on the medium voltage side make an adaptable voltage possible. Furthermore the voltage of the transformer could be regulated by an external circuit, similar to a RONT (adjustable mains transformer).