This guide provides general guidance on the steady-state performance requirements of high-voltage direct-current (HVDC) systems. It concerns the steady-state performance of two- terminal HVDC systems utilizing 12-pulse converter units consisting of three-phase bridge (double way) connections (see Fig 1). Excluded are multi-terminal HVDC transmission systems. Both converters are assumed to use thyristor valves as the main semiconductor valves and to have power flow capability in both directions. No consideration is given herein to diode valves. This guide, which covers steady-state performance, is accompanied by companion documents for dynamic and transient performance. All three aspects should be considered when preparing two-terminal HVDC system specifications. The user is cautioned to be aware of the difference between system performance specifications and equipment design specifications for individual components of a system. While equipment 1.1 Scope. This guide provides general guidance on the steady-state performance requirements of high-voltage direct-current (HVDC) systems. It concerns the steady-state performance of two- terminal HVDC systems utilizing 12-pulse converter units consisting of three-phase bridge (double way) connections (see Fig 1). Excluded are multi- terminal HVDC transmission systems. Both converters are assumed to use thyristor valves as the main semiconductor valves and to have power flow capability in both directions. No consideration is given herein to diode valves. This guide, which covers steady-state performance, is accompanied by companion documents for dynamic and transient performance. All three aspects should be considered when preparing two-terminal HVDC system specifications. The user is cautioned to be aware of the difference between system performance specifications and equipment design specifications for individual components of a system. While equipment Fig 1 WeIve-Pdse Converter Unit ?--. TRANSFORMER VALVE WINDINGS specifications and testing requirements are not defined in this guide, attention is drawn to many of those that could directly affect performance specifications for the system. Also excluded from this guide are the matters of detailed seismic performance requirements. In addition, because there are many variations between different possible HVDC systems, this guide does not consider these in detail, consequently it should not be used directly as a specification for a specific project, but rather to provide the basis for an appropriate specification tailored to fit an actual system's requirements.