Transient Overvoltage on a Bipolar HVDC Overhead Line Caused by DC Line Faults

Digital programs are used to investigate the overvoltages induced in one pole of a bipolar HVDC overhead line, and caused by a line-ground fault on the other dc pole. Various digital tests are carried out, bearing in mind in particular the nature of dc line termination at the converter stations, which may include filter circuits and a surge capacitor. It is shown that the terminal that looks inductive to a wavefront coming from the dc line is undesirable because it would cause high overvoltages at the terminal of the unfaulted pole. It is also shown that in order to reduce the risk of developing a double-pole outage from a single-pole fault, it is desirable to do away with the surge capacitor, if a suitable dc lightning arrester can be designed. Tests are presented in stages to isolate the effects of fault resistance, grid control, and line resistance. Results also indicate the restraints to be put upon the dv/dt line fault detection in order to avoid operation of this protection in the unfaulted pole.