ABSTRACT
The problem of electromagnetic compatibility of electronic equipment has arisen together with the advent of this kind of equipment, as it receives and transmits electromagnetic radiation. The DC flowing through the current transformer's (CT) primary winding leads to a rapid saturation of the core and to a significant distortion of the periodic component's shape and, subsequently, that of the secondary current. CT's secondary current curve has the same shape when subjected to a magnetizing inrush current when the powerful supply transformer is turned on. There are also specific digital protective relay (DPR) designs that provide fast computation of the second derivative of the current and use the obtained values for the threshold adjustment under the high nonperiodic component of the current. The study of microprocessor voltage relay with definite time delays showed that this delay heavily depends on this harmonic distortion.
