To what extent can rogowski coil current amplitude linearity be verified?

Calibrations of Rogowski coils at power frequencies are often performed at currents of only tens of amperes even though the coils are used at currents larger by two to three orders of magnitude, or even greater. The underlying assumption of an ideal linearity versus current amplitude is true for ideal coils. This paper addresses the question of practical significance as to what extent the linearity of real Rogowski coils versus current can presently be verified at power frequencies. For this task several different types of Rogowski coils were evaluated using a digital sampling system, with the best calibration uncertainties (k=2) of 50 μA/A for magnitude and 50 μrad for phase.