Metrological performances of voltage and current instrument transformers in harmonics measurements

In the new electrical system scenario, the increasing presence of non-linear loads and renewable energy sources makes the measurement of harmonics an essential task. The accuracy of harmonic measurement firstly depends on the used instrument transformers for voltage and current sensing. Since the behavior of instrument transformers in non-sinusoidal conditions is not always well defined, this paper presents an experimental study on the metrological performances of current and voltage instrument transformers (CTs and VTs) in the presence of harmonics. Proper tests procedures are defined and measurement setups are developed for both CTs and VTs calibration. The analysis is carried out by using test waveforms composed of a fundamental and one harmonic component. The harmonic ratio and phase errors are evaluated; the distortion effects on the errors on the fundamental component measurement are also investigated. The obtained results show how the metrological performances in harmonics measurement are influenced by both amplitude and phase shift of the harmonics.