For this reason, Power Quality (PQ) monitoring is becoming a fundamental task even in Medium Voltage (MV) networks. Measuring PQ at MV levels can only be performed using Instrument Transformers (IT) to step down voltage and current to levels suitable for PQ instrument input stages. However, no current international standard requires verification of errors introduced by IT in PQ phenomena measurement. Furthermore, this topic is only partially addressed in scientific literature, with articles focusing on specific and limited aspects of the issue. Therefore, this document aims to comprehensively evaluate the problem by proposing accuracy verification tests for various PQ parameters.

Firstly, a set of relevant PQ phenomena is selected for IT testing, along with their respective variation ranges, based on a review of applicable standards and scientific literature. For each selected PQ phenomenon, potential performance indices and test waveforms are proposed. Finally, the proposed procedure is validated by applying it to characterize two different types of commercial voltage transformers.