Investigating and Modeling the Harmonic Measurement Accuracy of Current Transformers

Overall measurement accuracy of current transformers is expressed by their accuracy class. When considering the fundamental component, it corresponds to ratio and phase error limits that are relaxed at small current values. As far as low-power current transformers, fixed ratio and phase error limits are prescribed at harmonic components. This paper shows, through numerical simulations, that this approach cannot represent the performance of current transformers in the presence of nonlinearity. A general method to model the behavior of harmonic ratio and phase errors is presented, regardless of the operating principle of the current transformer. This suggests an alternative approach to specify accuracy requirements at a given harmonic, which should depend on its relative magnitude with respect to the fundamental.