Abstract:
When the flexible dc grid recloses to a permanent pole-to-ground fault, a secondary overcurrent impact will be caused and then the system security will be threatened. In order to avoid this situation, a reclosing method that pre-judges the fault nature is required to ensure the effective restart and reliable recovery of dc system. Under the condition of the overhead line flexible dc system with hybrid dc circuit breaker, an adaptive reclosing technology for dc pole-to-ground fault based on dc current limiting circuit is proposed. Firstly, the topology of dc current limiting circuit is proposed and its working principle is analyzed. The topology is connected into dc line in series with hybrid dc circuit breaker, which is composed of current limiting unit, energy absorbing unit and fault nature identification unit. Then, combined with the dc fault development process, the equations of transient current and transient voltage in each stage are calculated theoretically, and the parameter selection method of each component of dc current limiting circuit is proposed. Finally, the dc pole-to-ground fault simulation is carried out in PSCAD platform, the simulation results show that the proposed adaptive reclosing technology can accurately identify the fault nature and endure great fault resistance.