Characterization of MV Instrument Transformers for Power Quality Measurement: the contribution from the IT4PQ project

Power Quality (PQ) monitoring in electrical transmission and distribution grids relies on the accurate measurement of wideband high voltages and high currents. Ensuring traceability of the measurements carried out is generally only partially accomplished by calibration of the low voltage (LV) PQ measurement instrument, whereas the calibration of the instrument transformer (IT) is mostly limited to the power frequency or performed at LV. In the paper, objectives and main outputs of the research project “Measurement methods and test procedures for assessing accuracy of Instrument Transformers for Power Quality measurements” (IT4PQ), which is focused on medium voltage (MV) grids, are outlined. An overview of the metrological framework developed within IT4PQ is given, together with details of the characterization of different types of MV ITs, both under controlled laboratory conditions and in the presence of influence parameters. Laboratory calibration measurement uncertainty is within a few hundreds of ppm and microradian up to 9 kHz, for ratio and phase errors respectively.