A New Method to Represent the Harmonic Measurement Accuracy of Current Transformers

Metrological performance of current transformers (CTs) is typically quantified in terms of ratio and phase errors. While they provide a good picture at the fundamental component, they are not as effective in condensing the accuracy of harmonic measurements in the presence of nonlinearity. This article proposes a new approach derived from the Volterra representation of the CT. The complex error has been adopted as the accuracy metric, split into a deterministic contribution (purely correlated with the measurand) and a circularly symmetric random term, whose spread depends on the fundamental magnitude; moreover, the proposed approach boils down to the usual ratio and phase errors if the CT exhibits negligible nonlinearity. The effectiveness of the developed method has been tested on an inductive CT, as a typical current transducer suffering from nonlinearity; nevertheless, results can be deemed as general since the approach has been derived from a behavioral model of the CT, and thus, independent of its operating principle. The impact of both measurement disturbances and uncertainty introduced by the nonideal calibration of the test setup has been also evaluated.