Calibration system and uncertainty budget for instrument transformers with digital output

This paper describes the reference system employed during calibration of instrument transformers with digital output. The reference system can be used for calibration of both current and voltage transformers by changing the references. The uncertainties associated with the calibrations of current transformers are evaluated and typical values are presented, including the established pool of variances for this calibration. This leads to a total uncertainty for transducer calibration of the same order of magnitude as that of analogue bridge calibrations in an industrial environment for traditional instrument transformers.