| Abstract | A synchronized current-comparator bridge for calibrating analog merging units at power frequencies of 60 and 50 Hz is described. Analog merging units take analog signals from instrument transformers, convert them into digital form, pack the sampled values into Ethernet frames conforming to the IEC 61850-9-2 LE specification, and stream the frames to other equipment in a digital substation for further processing. Since the sampled values are used for protection and metering, the merging units need to be calibrated. The expanded uncertainties (k = 2) of the described calibration system are estimated to be better than 15 μV/V for voltage magnitude, 15 μA/A for current magnitude, and 60 μrad for phase of either voltage or current. |
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