Improving the Accuracy of Current Transformers through Harmonic Distortion Compensation

It is common knowledge that conventional current transformers suffer from nonlinear effects due to the magnetization characteristics of their cores. Core saturation may occur because of large overcurrents or unidirectional transient components; however, weak nonlinear effects exist even during normal operation. The typical spectrum of current waveforms in ac power systems consists of a large fundamental component and harmonics having considerably smaller amplitudes. The fundamental term produces harmonic distortion which affects the measurement accuracy of current harmonics. This paper proposes a simple technique for compensating harmonic distortion occurring in current transformers. The effectiveness of the approach is assessed by means of numerical simulations; results show the remarkable improvement in measuring low order harmonics over a wide current range.