IEC/TR 60919-2:2008 provides guidance on the transient performance and fault protection requirements of high voltage direct current (HVDC) systems. It concerns the transient performance related to faults and switching for two-terminal HVDC systems utilizing 12-pulse converter units comprised of three-phase bridge (double way) connections but it does not cover multi-terminal HVDC transmission systems. However, certain aspects of parallel converters and parallel lines, if part of a two-terminal system, are discussed. The converters are assumed to use thyristor valves as the bridge arms, with gapless metal oxide arresters for insulation co-ordination and to have power flow capability in both directions. Diode valves are not considered in this report. This second edition cancels and replaces the first edition, published in 1991, and constitutes a technical revision. It includes the following main changes with respect to the previous edition: it concerns only line-commutated converters;isignificant changes have been made to the control system technology; some environmental constraints, for example audible noise limits, have been added; the capacitor coupled converters (CCC) and controlled series capacitor converters (CSCC) have been included.