After Jinping to Suzhou

Fulong to Fengxian and Yibin to Jinhua ultra-high voltage direct current (UHVDC) transmission projects in Sichuan province were put into operation in succession

if in any one UHVDC project a bi-pole block and stability control rejection fault should occur

a lot of surplus power will be generated and transferred in Sichuan power grid. It will result in the out-of-step separation device action between Chongqing and Hubei provinces and isolated power system operation in Sichuan-Chongqing. Over-frequency and instability will appear because of the insufficient tripping units and improperly chosen generators stipulated in the original scheme of Sichuan power grid. Therefore

in light of the new situation of putting multi-UHVDC projects into operation

the configuration principles presented should include avoiding unnecessary generator tripping during UHVDC commutation failure and after UHVDC successful restart

the prevention target of the scheme should only be for single UHVDC project bi-pole block and stability control rejection fault

every step generator-tripping amount should be controlled to avoid low-frequency load shedding and the generators’ UHVDC projects have top priority to be switched off because the over-frequency problem is due to the UHVDC power block faults. Finally

the improved scheme is presented and checked. The generator tripping setting value of research results has been applied to appointed units and a good effect will be obtained. This work is supported by State Grid Corporation of China (No. XT71-13-037).