The invention concerns a transformer system comprising an enclosure (1) housing a voltage transformer (4) and an electrical connection guided outside the enclosure (1) and electrically connected to the voltage transformer (4). Said electrical connection is for connecting the transformer system to a high or medium voltage installation. In order to be able to control easily the voltage on a high voltage installation, the invention proposes an improved transformer system whereby in the enclosure (1) is provided a decoupling device (12) for temporarily interrupting the electrical connection between the voltage transformer (4) and the first connector (6, said decoupling device capable of being actuated from outside the enclosure (1). Said transformer system enables to control the direct voltage without having to dismantle the high voltage installation.