Sereda O. Theoretical bases of development of digital technologies in systems of automation, diagnostics, control and protection of electrotechnical complexes.

Expediency of decomposition of signals representing complex oscillations into harmonic components by their discretization by multiplication by a lattice delta function with frequency less than twice the Nyquist frequency is theoretically substantiated and proved, which made it possible to expand the list of diagnosed emergency modes of distribution networks with voltage of 0.4 kV of trunk configuration. The theory of digital processing of analog signals by multiplying them by lattice delta functions with different discretization intervals is further developed, which allowed to accelerate the analysis of the harmonic spectrum of phase currents and currents in a neutral conductor in the presence of nonlinear distortions of their sinusoidal shape due to different load characteristics. The expediency of application of methods of digital processing of signals received from current sensors for formation of complex criteria of operation of the maximum current protections at interphase short circuits for the purpose of identification of emergency modes of operation of an electric network on degree of distortions of average square phase current values during transient mode is theoretically substantiated which allowed to reduce the sensitivity threshold of the maximum current protection to the level of currents of short circuits, the values of which are less than the starting currents of induction motors connected at the beginning of the power line. Procedures for digital processing of signals received from current sensors are established in order to extract information about such parameters of electric circuit as power factor and harmonic spectrum of phase currents, based on analysis of distorted under the influence of nonlinear loads and aperiodic component of rms values calculated in transient mode which does not exceed one period of change of phase electromotive force. Expediency of formation of criterion of operation of protection of neutral conductor against overload currents and currents of single-phase short circuits without involvement of harmonic analysis of spectrum of non-sinusoidal current, when purposeful distortion of rms value by selecting the appropriate discretization frequency of the output analog dependence allows not to take into account the value of the current of the third harmonic when constructing protection against single-phase short circuits and to take into account when constructing overcurrent protection. Is scientifically substantiated and proved Taking into account the development of the existing methodology in the field of digital signal processing theory, a set of scientific methods and research approaches to solving the topical scientific and applied problem of improving the protective characteristics of maximum current protection devices is developed, namely: • methods for determining the power factor of an electric circuit in the transient mode of overcurrent occurrence for the formation of a complex criterion for identifying the type of perturbation: remote short-circuit current or starting current of an induction motor; • a method of analysis of the harmonic composition of phase currents of non-sinusoidal shape for rapid identification of emergency modes of operation of power distribution networks in the presence of nonlinear loads; • a method of sliding monitoring of the rms value of current by applying a mathematical apparatus for integrating the squares of its instantaneous values obtained with determined discretization frequency of the output analog current dependence in time; • methods for diagnosing the thermal state of induction motors operating in repeated short-term operation mode by direct control of the temperature of the stator windings at start-up; • a method of thermal protection of induction motors at nonlinear distortions of sinusoidal shape of phase currents. Algorithms for digital processing of analog signals received from current sensors to ensure the operation of microcontroller control units for relay protection devices and emergency automation are developed, namely: • algorithms for rapid identification of the type of overcurrent, in particular starting currents of induction motors, for a time not exceeding one period of change of phase electromotive force after arising of perturbation of the electric circuit; • algorithms of circuit breakers microcontroller releases operation in case of neutral conductor break in any place of branched network with load distributed along the power line; • an algorithm of circuit breakers microcontroller releases operation in protection of neutral conductor from overload currents and single-phase short-circuit currents; • algorithms for diagnosing the thermal state of induction electric motors in the transient start-up; • an algorithm of operation of the relay of thermal protection of induction motors taking into account the higher harmonic components in phase currents.