The invention relates to an ultrahigh-
voltage DC line protection method based on specific
frequency band current, which comprises the steps of firstly extracting real-time current values measured by current dividers at a rectification-side protection installation part and a rectification-side
smoothing reactor valve side; calculating fault current of the protection installation part and the
smoothing reactor valve side, namely, the difference between the real-time current and steady-state current of an ultrahigh-
voltage DC
system in normal operation; extracting a specific
frequency band current component of the fault current by a filter; performing comparative judgment on a specific
frequency band current effective value at the rectification-side protection installation part, a specific frequency band current effective value at the rectification-side
smoothing reactor valve side and a protection threshold to obtain whether the DC line has a fault or not; and then obtaining the type ofthe fault. According to the invention, fault judgment is performed by only using the single-end specific frequency band current,
data synchronization is not required to be performed, requirements forthe sampling rate is low, and various DC line faults can be recognized quickly and accurately.