Теоретичні основи розвитку цифрових технологій в системах автоматизації, діагностики, контролю та захисту електротехнічних комплексів

Abstract

Дисертація на здобуття наукового ступеня доктора технічних наук за спеціальністю 05.09.03 – електротехнічні комплекси та системи, Національний технічний університет "Харківський політехнічний інститут", Харків, 2021. Дисертація присвячена розвитку теорії електромагнітних перехідних процесів в електротехнічних комплексах і системах низької напруги при несиметричних режимах роботи розподільних мереж електропостачання, а саме розробці теоретично обґрунтованого системного комплексу наукових методів застосування цифрових технологій для вдосконалення захисних характеристик апаратів релейного захисту та протиаварійної автоматики електричних мереж напругою 0,4 кВ. Теоретично обґрунтована та доведена доцільність розкладання сигналів, що являють собою складні коливання, на гармонійні складові, шляхом їх дискретизації множенням на ґратчасту дельта-функцію з частотою меншою за подвоєну частоту Найквіста, що дало можливість розширити перелік діагностованих аварійних режимів роботи розподільних мереж електропостачання напругою 0,4 кВ. Здобули подальший розвиток методи цифрової обробки аналогових сигналів шляхом їх множення на гратчасті дельта-функції з різними інтервалами дискретизації, що дозволило прискорити аналіз гармонійного спектру фазних струмів і струму в нейтральному провіднику за наявності нелінійних спотворень їх синусоїдальної форми внаслідок присутності нелінійних навантажень. Теоретично обґрунтована доцільність застосування методів цифрової обробки сигналів отриманих від датчиків струму для формування комплексних критеріїв спрацьовування апаратів максимальних струмових захистів при міжфазних коротких замиканнях з метою ідентифікації аварійних режимів роботи електричної мережі за ступенем спотворень середньоквадратичних значень фазних струмів. Встановлені процедури цифрової обробки отриманих від датчиків струму сигналів з метою вилучення інформації про такі параметри електричного кола, як коефіцієнт потужності й гармонійний спектр фазних струмів, виходячи з аналізу спотворених під впливом нелінійних навантажень й аперіодичної складової їх середньоквадратичних значень, обчислених в перехідному режимі зміни струму. Науково обґрунтована та доведена доцільність формування критерію спрацьовування захисту нейтрального провідника від струмів перевантаження та струмів однофазних коротких замикань без залучення гармонійного аналізу спектру несинусоїдального струму.The dissertation on competition of the scientific degree of the Doctor of Technical Sciences on specialty 05.09.03 – Electrotechnical Complexes and Systems, National Technical University “Kharkiv Polytechnic Institute”, Kharkiv, 2021. The Dissertation is devoted to the development of the theory of electromagnetic transients in electrotechnical complexes and low voltage systems with asymmetric modes of operation of power distribution networks, namely the development of a theoretically sound system of scientific methods and research approaches to digital technologies application to improve the protective characteristics of relay protection devices and emergency automation of electrical networks with voltage of 0.4 kV. 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, which allowed: to diagnose the violation of integrity of the neutral conductor at any place of the branch power transmission network with both linear and nonlinear loads without involving harmonic analysis of the phase current spectrum and to form criteria for operation of devices for protection of single-phase electricity consumers from overvoltages caused by a break in a neutral conductor; to improve the algorithm of protection of neutral conductor from overload currents and currents of single-phase short circuits by taking into account the harmonic current spectrum in the neutral conductor, which allowed in power supply networks with different load characteristics to take into account the third harmonic component of current selectively by selecting the appropriate discretization frequency of the intput analog time dependence; • 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, based on the analysis of the effect of changes in active resistance of the stator winding when changing its temperature on the non-uniform extreme values of instantaneous power consumption of the electric motor at start-up; • a method of thermal protection of induction motors at nonlinear distortions of sinusoidal shape of phase currents, which reduces the reduction of the sensitivity threshold of thermal protection of induction motors at overload currents by taking into account the influence of higher harmonic components in phase currents, namely the current of the fifth harmonic leading to additional losses and heating of the stator windings. 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, which reduced the sensitivity threshold of maximum current protection devices to the level of currents of remote short-circuits and to provide the mode of remote redundancy of failures of protections; • 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, in which in the presence of nonlinear loads the formation of protection criterion is carried out due to widely used in relay protection and emergency automation devices mathematical operations of integration of squares of instantaneous values of phase currents without involvement of the analysis of their harmonic structure; • an algorithm of circuit breakers microcontroller releases operation in protection of neutral conductor from overload currents and single-phase short-circuit currents, which is based on sliding monitoring of rms value of current in neutral conductor in mode when purposefully distortions are introduced in calculating the rms value of the current by selecting the appropriate discretization frequency of the input analog dependence which allowed not to take into account the value of the current of the third harmonic in the construction of protection against single-phase short circuits and to take into account at the implementation of overload protection to ensure full selectivity of protection of distribution networks of 0.4 kV with deaf neutral grounding with both linear and nonlinear loads without the involvement of harmonic analysis of the current spectrum in a neutral conductor; • algorithms for diagnosing the thermal state of induction electric motors in the transient start-up mode by directly controlling the temperature of the stator winding by changing its active resistance when heated, the essence of which is to analyze the non-uniformity of extreme values of instantaneous and quasi-instantaneous power consumption in the mode of occurrence of starting current; • an algorithm of operation of the relay of thermal protection of induction motors taking into account the higher harmonic components in phase currents, namely the current of the fifth harmonic, which leads to additional losses and heating of the stator windings.