Development of a system for the calibration of digital bridges for non-conventional instrument transformers

This paper describes a development of a calibration system at National Research Council (NRC) Canada for digital bridges, which are in turn used for calibrations of non-conventional current transformers. A pre-calculated set of digital data is generated in accordance with the IEC 61850-9-2 LE specification for data transmission in power substations and synchronized to 1 pulse-per-second (PPS) signal. A known current is created and provided to the digital bridge under test. The ratio and phase errors of the digital bridge are determined by a digital sampling system. The expanded uncertainties (k=2) are estimated to be better than 100 μA/A for magnitude and 100 μrad for phase.