IEC 61975:2010+A1:2016 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. system. The tests specified in this standard are based on bidirectional and bipolar high-voltage direct current (HVDC) installations which consist of a sending terminal and a receiving terminal, each connected to an a.c. 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. 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. This edition cancels and replaces IEC/PAS 61975 published jointly in 2004 by IEC and CIGRÉ. It constitutes a technical revision incorporating engineering experience. This consolidated version consists of the first edition (2010) and its amendment 1 (2016). Therefore, no need to order amendment in addition to this publication.