Method for operating a converter station of an electrical rail network by means of a network regulator, wherein the electrical rail work comprises overhead contact lines and substations (11, 12) with common bus bars (211, 212), wherein the converter station is arranged adjacent to the substations (11, 12) and comprises a converter and a further common bus bar, wherein the converter is able to set the voltage at the bus bar of the converter station such that it substantially has the same amplitude, frequency and phase position as on the common bus bars (211, 212) of the substation (11, 12), characterised in that because of a disrupted transmission of the voltages (u v1, u v2) from the substations (11, 12): - from a voltage (u 1B) measured at an output of a transformer coupled to the converter, its base oscillation amplitude (u 1B(a)) is determined, - a nominal base oscillation amplitude (u* 1B(a)) and a nominal power factor (cosφ*) are predefined, wherein the nominal base oscillation amplitude (u* 1B(a)) and the nominal power factor (cosφ*) are estimated, for example before the network regulator is brought into use, and/or the nominal base oscillation amplitude (u* 1B(a)) and the nominal power factor (cosφ*) are determined and stored at predefined time intervals during functional operation of the transmission of the voltages (u v1, u v2) from the substations (11, 12), - from the base oscillation amplitude (U 1B(a)) and the nominal base oscillation amplitude (u* 1B(a)), an apparent power nominal value (S* B) is determined, - from the apparent power nominal value (S* B) and the nominal power factor (cosφ*), an active power nominal value (P* B) and a reactive power nominal value (Q* B) are determined, and - from the active power nominal value (P* B) and the reactive power nominal value (Q* B), a nominal voltage is determined in order to set an output voltage of the converter so as to minimise the transmission losses over the overhead contact lines. - from a voltage (u 1B) measured at an output of a transformer coupled to the converter, its base oscillation amplitude (u 1B(a)) is determined, - a nominal base oscillation amplitude (u* 1B(a)) and a nominal power factor (cosφ*) are predefined, wherein the nominal base oscillation amplitude (u* 1B(a)) and the nominal power factor (cosφ*) are estimated, for example before the network regulator is brought into use, and/or the nominal base oscillation amplitude (u* 1B(a)) and the nominal power factor (cosφ*) are determined and stored at predefined time intervals during functional operation of the transmission of the voltages (u v1, u v2) from the substations (11, 12), - from the base oscillation amplitude (U 1B(a)) and the nominal base oscillation amplitude (u* 1B(a)), an apparent power nominal value (S* B) is determined, - from the apparent power nominal value (S* B) and the nominal power factor (cosφ*), an active power nominal value (P* B) and a reactive power nominal value (Q* B) are determined, and - from the active power nominal value (P* B) and the reactive power nominal value (Q* B), a nominal voltage is determined in order to set an output voltage of the converter so as to minimise the transmission losses over the overhead contact lines.