DC harmonics of HVDC series tapping stations

The DC characteristic harmonics of an HVDC series tapping station are analyzed from three points of view: the generated magnitudes; the magnitudes entering the DC transmission line sections; and reduction of the generated magnitudes by various differential firing algorithms. The theoretical analysis is supported by digital simulation studies of a 10% series tap incorporated in the Bipole II of the Nelson River HVDC system. The application or elimination of DC harmonic filters at the tapping station depends, among other factors, on the lengths of the DC line sections between the tapping and the main converter stations.