A measurement system for the calibration of MV instrument transformers under non sinusoidal conditions

The metrological characterization of instrument transformers is a well-known process when it is carried out under sinusoidal conditions. On the other hand, because of the increasing presence of distorting loads such as power electronics converters, often the voltage and current waveforms cannot be considered sinusoidal. In this scenario, the accurate measurement of harmonic components becomes very important both for billing as well as for power quality monitoring. Therefore, the whole process of instrument transformer calibration should be reconsidered in order to take into account their actual behavior also under these operating conditions. In this paper a new setup for the calibration of MV voltage instrument transformers is presented. It is based on two parts: a voltage generator able to supply the transformer under test with an arbitrary voltage signal and a digital signal processing procedure allowing to evaluate the ratio and phase errors of the transformer with a high accuracy, over an extended frequency range.