With the commissioning of 500 k V line-reconstructed project and 10 sets of 300 MVA phase modifiers in Suzhou southern power grid

both static/dynamic reliabilities of the grid have been improvedgreatly and

thereby

the short-circuit currents level has also improved. At the same time

Suzhou south-ern power grid

as typical big receiving grid

its main UHV Jinsu DC has such feature as strong season

which causing such problems as big risk of DC communication of power grid and multiple emergency powerlimit after DC bipolar lockout. Addition of 500kV series reactor in Meili-Huiquan line can effectively con-trol the short circuit current level of 500kV substation in Suzhou southern power grid. Operation of 500 k Vunified power flow controller（UPFC）can improve significantly the undertaking capability and support function of Suzhou southern power grid to UHV DC power grid. In this paper

as for the grid structure and of Su-zhou southern power grid at different stage and the function from UPFC

the resistance selection of seriesreactor is analyzed. On the base of coordination and optimization of series reactor and unified flow control-ler

the resistance of reactor not only meeting both the control requirement of short circuit current

but also making the flow regulation function of UPFA flow is proposed.