This International Standard applies to system tests for high-voltage direct current (HVDC) installations which consist of a sending terminal and a receiving terminal, each connected to an a.c. AC system. The tests specified in this standard are based on bidirectional monopolar and bipolar high- voltage direct current (HVDC) installations which consist of a sending terminal and a receiving terminal, each connected to an a.c. AC system. The test requirements and acceptance criteria should be agreed for back-to-back installations, while multi-terminal systems and voltage sourced converters are not included in this standard. For monopolar HVDC installations, the standard applies except for bipolar tests. For the special functions or performances that are claimed by specific projects, some extra test items not included in this standard should be added according to the technical specification requirements. This standard only serves as a guideline to system tests for high-voltage direct current (HVDC) installations. The standard gives potential users guidance, regarding how to plan commissioning activities. The tests described in the guide may not be applicable to all projects, but represent a range of possible tests which should be considered. Therefore, it is preferable that the project organization establishes the individual test program based on this standard and in advance assigns responsibilities for various tasks/tests between involved organisations (e. g. user, supplier, manufacturer, operator, purchaser etc.) for each specific project.