A new high-accuracy system for power-frequency calibration of Rogowski coils is described in this paper. The calibration system is based on nonsynchronous digital sampling. An automated prototype of the calibration system operates at currents of up to 2000 A. A semiautomated system is capable of operating at currents of up to 60 000 A. The best uncertainty (k = 2) of the calibration system is estimated to be better than 50 muA/A for magnitude and 50 murad for phase.