The hidden dangers analysis of the control logic on HSGS switch in Guizhong station

Restricted by the Earthing electrode current, the metal return becomes the most commonly connection in converter stations after unipolar blockade or unipolar outage. Therefore, it is very important for the safety and stability of the whole HVDC system whether the switching operation between single-pole ground return and single-pole metal return is safe and stable. Combined with the interlock logic of HSGS switch (high speed grounding switch) in Guizhong Station and the simulation operation, this paper analyzes the operation sequence of metal return, and points out the interlocking logic provided by the DC station control system can not prevent the risk of DC unipole locking caused by human misoperation under specific conditions. In addition, according to the current topological relationship in the operation of metal return, this paper presents a scientific modification plan with electric quantity interlocking, which can prevent the operators from misoperation and provides reference for the interlocking logic to other HVDC transmission system.