Conversion station between a high-voltage alternating network and a high-voltage continuous network (121, 123, 131, 133), characterized in that it comprises: - a connection interface to a polyphase alternating network; - a connection interface to a continuous network, having first and second poles (441, 442); - an AC/DC converter; - for each of the phases: - the AC/DC converter has a first conversion arm connected between an intermediate node and the first pole, and a second conversion arm connected between the intermediate node and the second pole, the AC/DC converter being connected between the first and second poles in symmetrical monopolar mode, the intermediate node being connected to the connection interface to the alternating three-phase network; characterized by - a balancing circuit for the voltages of the first and second poles, including a controlled switch and an inductor connected in series between earth and the intermediate node; - a control device configured to detect an electrical fault between one of the first or second poles and earth, and configured to control the closing of said controlled switches of each of the phases when an electrical fault is detected. - a connection interface to a polyphase alternating network; - a connection interface to a continuous network, having first and second poles (441, 442); - an AC/DC converter; - for each of the phases: - the AC/DC converter has a first conversion arm connected between an intermediate node and the first pole, and a second conversion arm connected between the intermediate node and the second pole, the AC/DC converter being connected between the first and second poles in symmetrical monopolar mode, the intermediate node being connected to the connection interface to the alternating three-phase network; characterized by - a balancing circuit for the voltages of the first and second poles, including a controlled switch and an inductor connected in series between earth and the intermediate node; - an AC/DC converter; - for each of the phases: - the AC/DC converter has a first conversion arm connected between an intermediate node and the first pole, and a second conversion arm connected between the intermediate node and the second pole, the AC/DC converter being connected between the first and second poles in symmetrical monopolar mode, the intermediate node being connected to the connection interface to the alternating three-phase network; characterized by - a balancing circuit for the voltages of the first and second poles, including a controlled switch and an inductor connected in series between earth and the intermediate node; - the AC/DC converter has a first conversion arm connected between an intermediate node and the first pole, and a second conversion arm connected between the intermediate node and the second pole, the AC/DC converter being connected between the first and second poles in symmetrical monopolar mode, the intermediate node being connected to the connection interface to the alternating three-phase network; - a balancing circuit for the voltages of the first and second poles, including a controlled switch and an inductor connected in series between earth and the intermediate node; - a control device configured to detect an electrical fault between one of the first or second poles and earth, and configured to control the closing of said controlled switches of each of the phases when an electrical fault is detected.