Keywords: 
• converter transformer /
• commissioning test /
• insulation resistance value /
• dielectric loss /
• low frequency load short circuit current heating /
• project progress

Abstract: [Introduction] Converter transformer is the most critical equipment that restricts the construction progress of the whole converter station project. The insulation resistance test of converter transformer is often unqualified in the field transfer test, which has a great impact on the construction progress of the project. If not qualified, it may bury the hidden trouble of safe operation in the future operation. [Method] The causes of nonconformity of insulation resistance test of 4 high-end converter transformers in an UHVDC project were analyzed in detail, various factors causing nonconformity of indexes are investigated, a comprehensive treatment scheme was developed and practical verification was carried out. [Result] The results show that according to different conditions, the method of reducing the dielectric loss of insulating oil or heating with low frequency load short circuit current or replacing insulation oil as a whole can be used to deal with the insulation resistance problem. [Conclusion] This paper can provide some ideas and methods for other similar engineering problems, which can ensure the quality and minimize the influence on the progress of the project.