Abstract: In the operation of a control arrangement for the direct voltage of an inverter station which inverter station includes a plurality of thyristor bridges which are connected in series at their direct voltage side and connected to a three-phase mains via a plurality of variable ratio transformers each individually associated with a respective thyristor bridge, a plurality of extinction angle circuits each associated with a respective thyristor bridge, and a total control circuit for controlling the voltage of all thyristor bridges together, the control circuit providing an output corresponding to the direct voltage of the inverter station and responding to a setting value representative of the transformer stage adjustment which operates in synchronism for all thyristor bridges, the control arrangement is matched to the control path by comparing a measured value which corresponds to the direct bridge voltage of each thyristor bridge with the instantaneous maximum value of the measured values for all thyristor br

Abstract: In order to monitor the conduction cutoff phase angles of a plurality of controllable rectifiers arranged in two groups in a rectifier bridge, a signal proportional to the angle for each rectifier is stored in a respective sample and hold member after each occurrence of a positive blocking voltage at that rectifier, and the minimum of the currently stored signals is observed.