Restoration strategies for the South China interconnected power system after generator tripping following DC system fault

When such severe contingency as double pole block fault arouses instability in the South China Interconnected Power System (SCIPS), selective tripping of generating units in the sending end has to be used as a method to maintain system stability. In case the tripped units go through a shutdown and cold start cycle for long duration, it is desirable that they should be hot started and resynchronized to the system as soon as possible to make a quick recovery of the system after fault. Under conditions where the DC fault is permanent, however, such objective is difficult to achieve. This paper presents a control strategy that power generation of some running units be reduced during this process to permit the tripped units to be resynchronized to the system without changing the power level at the sending end, which enables the tripped units to be restored to load rapidly without disturbing system stability. With user models developed in PSS/E, simulations were performed on the SCIPS to investigate the system behavior during reloading process of those thermal units which had been tripped following DC block fault. The results show that power generation at the sending end can be maintained at a reasonable steady level when output of some running units are appropriately reduced during the reloading process of the thermal units, thus having little impact on the system stability, which demonstrates the feasibility and effectiveness of the proposed scheme.