In-situ test assessment of thyristor level in the converter valve of HVDC power transmission

The thyristor level is the basic unit of HVDC converter valve, which is the core equipment in the HVDC power transmission system. Because the converter valve performance directly affect the reliability, stability and efficiency of the whole power system, each thyristor level in the converter valve needs to be test routinely during the maintenance period of the converter valve equipment. Currently there is no specific and detailed test scheme for the thyristor level with thyristor control unit (TCU). Therefore, it is particularly urgent to study the in-situ test technology for the thyristor level in the HVDC converter valve. In this paper, the in-situ test principle, content and methods for the thyristor level with TCU are presented based on the analysis of the thyristor level working principle and the IEC 60700-1-2008 standard in order to offer technical support for the operation and maintenance of the HVDC converter valve. In general, the reverse recovery period of thyristor level is the most vulnerable stage of thyristor operation process, so a transient high-voltage pulse is applied to the thyristor level during its reverse recovery period in order to test the characteristics of thyristor level. Then, the in-situ test method for the thyristor level is applied to the converter valve test of ±800kV HVDC power transmission project, and the practical test result verifies the reasonability and validity of the proposed in-situ test method.