For this reason, PQ monitoring is becoming a fundamental task even in medium voltage (MV) networks. Measuring PQ at MV levels can only be done using instrument transformers (IT) to reduce the voltage and current to levels suitable for the input stage of PQ instruments. However, no international standard currently requires the verification of errors introduced by IT in the measurement of PQ phenomena.

Furthermore, this issue is only partially addressed in the scientific literature, where articles tend to cover specific and limited aspects of the problem. Therefore, this paper aims to comprehensively evaluate the issue by proposing verification tests for IT accuracy across various PQ parameters. First, a set of relevant PQ phenomena for IT testing, as well as their variation ranges, is selected based on a review of applied standards and scientific literature. Possible performance indices and test waveforms are proposed for each selected PQ phenomenon. Finally, the proposed procedure is validated by applying it to the characterization of two different types of commercial voltage transformers.