Expressing Uncertainty of Voltage Transformers: A Proposal

Voltage transformers are vital components for the operation of power systems. Because of the increasing diffusion of power electronics, nonlinear devices in distribution grids, their role is becoming even more important, since they represent the input stage in power quality monitoring instruments. Nevertheless, their metrological performances are still expressed in terms of accuracy class, namely rating maximum ratio and phase errors at fundamental and harmonic frequencies. The aim of this work is providing a contribution that allows migrating from the concept of maximum error to that of uncertainty. Calibration of an inductive voltage transformer has been considered as a case study and simulated through detailed modeling; this allows neglecting the impact of noise and that of the reference transducer. The statistical features of the measurement error are evaluated, and a method to quantify and express uncertainty is proposed.