International Comparison of Current Transformer Calibrations

An international comparison of current transformer calibrations between five metrology laboratories has been conducted. The measurements were made at current ratios ranging from 1 A: 1 A to 200 A: 1 A at 10, 100, and 200 percent of rated current and from 5 A: 5 A to 200 A: 5 A at 1, 10, 100, and 200 percent of rated current, at a frequency of 50 Hz. Several ratios have also been compared at 60 Hz. Except at some low-level currents the results show very good agreement among the five laboratories. The current differences are typically within ??1 ppm and the phase displacements within ??1.5 ??rad.