High-Frequency Distortion (HFD) in both Low Voltage (LV) and Medium Voltage (MV) grids is gaining growing interest from the scientific and technical community due to its increasing occurrence and the issues they can cause. Furthermore, the phenomenon of HFD is expected to rise as it primarily stems from newly installed devices essential for achieving decentralized generation from renewable sources. To monitor HFD in MV grids, the use of Instrument Transformers (ITs) is essential to scale down voltages and currents to levels compatible with the input stages of Power Quality (PQ) instruments. In this respect, the recently released edition 2 of the IEC 61869–1 standard extends the IT accuracy class concept up to 500 kHz. However, within the IEC 61869 standard family, guidelines for testing ITs only exist at power frequency, lacking information on the procedure and setup for assessing the frequency behaviour of ITs. This paper proposes a flexible architecture for generating realistic currents with superimposed HFD. It involves the use of two current sources, one devoted to the generation of a fundamental tone at rated amplitude (theoretically up thousands of ampere) and frequency (DC or AC 50/60 Hz) and one for the superimposition of tones at reduced amplitude and frequencies in the HFD range. Through preliminary tests, the applicability of this proposed architecture has been experimentally validated and it is presented in this paper.