Setup and Characterisation of Reference Current-to-Voltage Transformers for Wideband Current Transformers Calibration up to 2 kA

This paper describes the setup and characterisation of a set of wideband Current-to-Voltage (C-to-V) transformers equipped with a symmetrical winding arrangement on its primary side. The transformer set is being developed at PTB and contributes to the European project “FutureGrid II – metrology for the next-generation digital substation instrumentation”. The objective of this paper was to use the reference transformer to calibrate the digital instrument transformer (IT) not only accurately at power frequency but also stably within a wider bandwidth. The calibrated errors of the first current transformer (CT), which is known as CT50, were within ±5 ppm and μrad at 50 Hz. The uncertainty of the CT50 was ±6·10-6 for the ratio and phase errors (k = 2). The frequency response errors of the CT50 up to 12 kHz were below 0.1 % and 0.2 crad with the expanded uncertainties below ±1·10-4 for the ratio errors and ±3·10-4 for the phase errors (k = 2)