ABSTRACT
The problem of electromagnetic compatibility (EMC) of electronic equipment has arisen together with the advent of this kind of equipment, as it receives and transmits electromagnetic radiation. Thus, the high-frequency component of interference can propagate into hardware, bypassing the filters and protective elements. Time-current characteristics of digital protective relays (DPR) are not maintained, sectors of remote protection are determined incorrectly, and so on. There are also specific 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 harmonic distortion of the voltage and current entering the DPR input represent the components with higher frequencies, compared to the main frequency. With regard to the impact of pulse-switching surges of mains, they are less dangerous for DPRs as they arrive at an internal switched power supply, which includes input filters, high-voltage electronic components, and varistors.
