GB/T 22389 is the Chinese standard for gapless metal-oxide surge arresters used in high-voltage direct-current converter stations. It was prepared through a modified adoption of the corresponding international standard for HVDC converter station arresters, with national provisions added where Chinese practice or service conditions required them, and it fills a gap that the alternating-current arrester standards cannot cover. An HVDC converter station contains arresters in a greater number of positions and with a wider range of duties than an alternating-current substation: arresters protect the converter valves, the converter transformers, the smoothing reactors, the direct-current busbars and the filters, and each position imposes a different combination of continuous voltage, energy and steepness of the current that the arrester must tolerate. The standard therefore classifies the arresters by function and location, defines the corresponding test requirements, and specifies the procedures for the residual voltage, impulse current, operating duty and energy capability tests together with the selection and coordination rules.