Compensation of Current Transformers' Non-Linearities by Means of Frequency Coupling Matrices

Current transformers (CTs) are the most commonly installed current transducers in power systems, at all voltage levels. Therefore, the measurement of harmonics, and power quality in general, which is an essential task in the new context of Smart Grids, are strongly influenced by the performance of CTs. It is well known that CTs can exhibit a nonlinear response and, therefore, in order to accurately measure harmonics with CTs, suitable non-linear mathematical models have to be used. In this paper the complex ratio of the CT is modelled using a frequency domain model based on frequency coupling matrices. An accurate measurement setup has been built to characterize the CTs performance in distorted conditions. Some preliminary results of the proposed compensation technique are presented and discussed for a commercial CT of accuracy Class 0.5.