First the necessity of bipolar operation with station ground mat in Puer rectifying station of Puqiao ultra high voltage direct current(UHVDC)replacing electrode is analyzed

and then the bipolar operation feasibility is studied in depth

including verification of thermal stability of station ground mat

verification of contact voltage and stepping voltage are checked. Some control and protection optimizations are proposed to avoid big current injecting into station ground mat and ensure the safety of system

people and equipment

including synchronous unlock and lock logic

bipolar current tracking

bipolar synchronous tripping logic

76SG and 87GPS protection in rectifying station and 60EL in inverting station. On-site operation shows that optimizations of direct current(DC)station control

pole control and DC protection can satisfy bipolar operation with station ground mat

and the safety requirements of primary equipment

secondary equipment and people all can meet the proposed standards.