Fault recovery control for islanding operation of yunnan-guangdong UHVDC transmission system after mono-polar blocking

Islanding operation at the sending terminal of Yunnan-Guangdong UHVDC transmission project was designed as one of the normal operation modes. In order to use this mode, it should be verified that the UHVDC and the islanding AC system can withstand impacts of various faults that may occur during real system operation. The DC system mono-polar blocking is one of the serious faults that the islanding operation must be able to withstand. Based on the islanding operation on-site commissioning tests, the fault recovery process after mono-polar blocking under rated DC power operation was analyzed. Using electromagnetic transient simulations, the resonance issue caused by shedding partial generation units in the islanding system for over-frequency control after the mono-polar blocking was investigated. The coordination control of tripping surplus reactive power compensation units at converter station and shedding partial generation units for improving the fault recovery characteristic was evaluated. The analysis supports the real system operation using islanding operation mode.