Device for transforming and for rectifying polyphase, in particular three-phase, voltage comprising a polyphase transformer comprising a voided central zone, a voltage rectifier circuit that is connected to the transformer and a fan. The voltage rectifier circuit includes at least three heat dissipation units forming a right prism of regular polygonal section comprising a voided central zone, the transformer, the voltage rectifier circuit and the fan being positioned such that at least some of the airflow produced by the fan flows through the voided central zone of the rectifier so as to immerse the transformer.