Adaptability Analysis of Pilot Differential Protection for Hybrid Cascaded UHVDC Transmission Lines
To explore the adaptability of the existing pilot differential protection for the dc lines to the hybrid cascaded ultra-high-voltage direct current(UHVDC)transmission system,combined with the operation modes of this system,the fault characteristics and protection adaptability of the dc system faults at different locations under three special operating modes are analyzed by theoretical analysis and simulation.The theoretical analysis shows that the pilot differential protection is good in adaptability.The simulation analysis shows that the DC line distribution capacitance and the modular multilevel converter(MMC)control characteristics of the inverter side may cause the dc line current delayed self-decrement to fluctuate for a long time during a DC line fault,resulting in a very long lockout duration of the pilot differential protection.Currently,the system suffers the super fault current impact of the MMC for a long time.When there is a failure outside the DC line area,the DC current difference between the rectifier side and the inverter side may have a large absolute value and be in a fluctuating state for a long time,existing a risk of incorrect operations in the pilot differential protection.
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万方数据
维普
