Supplementary comparison EURAMET.EM-S35: comparison of high-current ratio standard. Final report.

The primary scope of the comparison was the validation of CMCs for quantities related to dc high currents, for current values ⩾ 100 A. The travelling standards were two direct-current current transformers (DCCT). The measurand was the current ratio of the DCCT, having a nominal value R = 1:1500, to be measured at primary currents of 90 A (mandatory), 300 A and 600 A (optional). The measurement results could to be stated for positive and negative currents, and/or as an average of the ratios obtained with both current polarities. The comparison involved twelve participants (two pilot laboratories included), eleven of them measured the travelling standard, and ten provided results. Two participants withdrew due to technical problems. The comparison was organized into two loops, where the participants of each loop measured only one of the two travelling standards, while the pilot laboratories measured both standards, and making possible the linking of measurement results of the participants of loop 1 with those of loop 2. The circulation of the standards started in December 2012 and ended in June 2015. Concerning the measurement results, a good agreement was achieved, although the travelling standard instability of loop 1 represented a relevant contribution to the DOE uncertainty, which is significantly larger than the measurement uncertainty declared by some participants.