An AC current transformer measuring system for power frequencies

This paper describes the design and setup of the new AC current transformer calibration system at PTB, which uses enhanced actively compensated current comparators (CCs) for rated primary currents from 5 A up to 60 kA and a new current transformer bridge based on the differential method. The bridge makes use of modern high-resolution analog-to-digital converters and makes it possible to connect traditional current transformers (CTs) as well as two-stage CTs with rated secondary currents from 100 mA to 5A. The lower current ranges are integrated to enable a calibration of CTs of the highest available precision for national power standards. The current sensors and the two-channel sampling system of the bridge allow a resolution in the order of 10
^-10
, while the estimated Type-B uncertainty of the bridge is in the range of 10
^-8
.