ABSTRACT
UHV AC/DC power system will be developed rapidly as the backbone grid of the strong and smart grid, and the “five vertical and five horizontal” backbone grid of UHV AC and 27 project of UHV DC will be built in the future[9]. A larger bias current is detected through the substation near the DC grounding electrode. When the UHVDC is operated unipolar and full-load of a province in May 2014 (the ground current is 5000 A), the number of the substations, which has the neutral bias current nearby is greater than 200 A, between 100-200 A and between 20-100 A, is about 3, 2, 19 respectively. At present, a substation that contains AC transformers and converter transformers is adopted to the converter substations including the Shenzhen, Bao’an and Baoji in ± 500 kV HVDC project and Huidong in ± 800 kV HVDC project, in which the distribution and suppression measures are more complicated.
