COMPUTER MODELS OF CURRENT TRANSFORMERS IN THE PRESENCE OF HARMONIC DISTORTION

A theoretical analysis of CTs behavior has been developed by means of the equivalent circuit. The CTs performance under distorted conditions is usually characterized by means of the frequency response test. Models of the instrument transformers are especially important for studying Maturation, ferro-resonance phenomena, harmonics and sub-harmonics and their effect on the performance of projective. relaying. The main features of the two CT models are analyzed. Some issues about the initial magnetic flux estimation ore addressed. CTs errors are strong influenced by the waveform of the primary current. A procedure for the on-line estimation of the primary current, based on a self-scheduling nonlinear technique is discussed.