This work considers the problems in relay protection at magnetic conductors’ saturation of current transformers, as a rule, followed by occurrence in currents of the aperiodic components that has negative effect on work of relay protection. Time during which proportions between primary and secondary currents are broken can reach a half of time and even more than existence of short circuit. The algorithm of calculation of the current values of the secondary currents that are sharply reducing the size of aperiodic components is offered. Thereby practically only periodic components are brought to relay protection. The algorithm is based on selection for calculation of three values removed in a row and gives aperiodic component at the time of average measurement. It is offered the algorithm of determination of the current values of currents and their derivatives in “future” time points including magnetic conductors’ saturation of current transformers when it is required to turn on automatic equipment of management of the modes.

short-circuit current, relay protection, aperiodic component, transformer, digital filter, distortion of secondary currents at magnetic conductors’ saturation of current transformers, an exception of aperiodic components in secondary currents, a sampling interval, algorithms of determination of the current values and their derivatives.