Calibration of electronic transformer with digital output based on synchronous sampling

This paper describes a calibration system based on digital sampling of the reference synchronized to the pulse-per-second (PPS) signal of the merge unit (MU) for electronic transformer (ECT/EVT) under test. This calibration system is designed in conformity to the IEC61850-9-2LE standard for digital substation. The reference system included a two-stage CT up to 10 kA, a non-inductance shunt, reference VTs up to 220 kV/√3, an inductive voltage divider (IVD), a sampling voltage multimeter (DVM), a function generator(FG), a fiber-Ethernet converter and a clock synchronization device. Software for instrument control, packets capturing and a compensated discrete Fourier transform (DFT) algorithm were developed for the system. Uncertainty evaluation proved that this reference system is qualified for calibrating electronic transformers (ETs) with an accuracy class of 0.1S/0.1.