Academic literature on the topic 'Non-sinusoidality'

The results of measurements of the harmonics components of the current, voltage, power of harmonics at the point of connection of electric receivers with a non-linear voltage-current characteristic are considered. It is shown that the amount of electric energy including the non-sinusoidality of the currents and voltages consumed by the non-linear load is less than the amount of the fundamental frequency energy. The difference between them is the harmonic distortion energy that causes extra losses to the electric networks. The voltage harmonic distortions at the measurement point exceed the normative values for 0.4 kV electric networks.

The paper is dedicated to the investigation of electric energy quality in AC traction network. The object of investigations is voltage in the AC traction network on buses of 27.5 kV in the AC functioning substation. The probabilistic-statistical value of the voltage level and values of electric energy quality according to voltage non-sinusoidality is under fulfillment. There are shown numerical characteristics and histograms of the distribution density of values under analysis for two operation modes of the AC traction substation – switching on and off of the longitudinal capacitive compensation device formed on the basis of natural measurements. The probabilistic-statistical processing of natural measurements results in power supply arms of the functioning traction substation located in the Far-East of the Russian Federation is carried out. The analysis results are shown as distribution density histograms of random values according to the standard law and in a table form. The longitudinal compensation device impact upon quality values of electric power according to the voltage is under consideration. The calculated indices of electric power quality at the traction substation are compared with the requirements of GOST 32144-2013 in force. It is mentioned that upon buses of 27.5 kV of the traction substation both in the mode of UPK switching on, and in the mode of its switching off the electric power quality by the factor of voltage harmonic components does not satisfy the requirements of GOST 32144-2013 in a number of harmonics. On the basis of the complex estimate of voltage parameters there is drawn a conclusion of the positive impact of longitudinal capacitive compensation devices upon voltage level and the absence of a distinct effect upon a harmonic structure of voltage in a traction network at longitudinal compensation switching on. The conclusion is drawn about filtration expediency of voltage highest harmonic components in power supply arms of the traction substation to bring quality indices on voltage non-sinusoidality to the requirements of the standard in force.

Object and purpose of research. This paper discusses electric propulsion system of leader icebreaker. Its purpose was to develop mathematical and computer-based model of electric propulsion drive powered by asynchronous motor with three stator windings for further investigation of steady, transitional, asymmetric and emergency operation scenarios of electric power and propulsion system for the leader icebreaker. Materials and methods. Hardware and methods for computer-based simulation of complex engineering structures. Main results. Development of the mathematical model representing asynchronous motor with three windings in phase coordinates. Computational studies on direct startup of 15 MW propulsion motor, as well as on steady and transitional operational conditions of ship electric power system consisting of 36 MW synchronous genset, two-winding transformers and electric propulsion drive with 15 MW asynchronous motor in phase coordinates with three stator windings and three-level frequency converter. Calculation of voltage non-sinusoidality ratio for MSB buses with operation of 15 MW propulsion motor driven by 36 MW synchronous genset. Conclusion. Mathematical model of asynchronous motor suggested in this paper could be used to calculate steady and transitional operation scenarios of marine power systems with frequency-controlled three-winding asynchronous motor, as well as to calculate electromechanical and electromagnetic processes and refine frequency control algorithms. This is especially relevant because each of the asynchronous electric machines used in the electromechanical assemblies of leader icebreaker propulsion motors has three stator windings, and this icebreaker is the first experience of applying a 15 MW marine electric drive.

The existing calculation methods in various sources represent rectifier installations as sources of higher harmonics. In this case, the current value of the primary winding of the transformer in the form of rectangles is decomposed into a Fourier series and harmonic components of the current are obtained, except for the main harmonic higher 5, 7, 11, 13, 17, 19 The amplitudes of the current of the higher harmonics are multiplied by the inductive resistances of the supply network corresponding to the frequencies, the results are squared and summed up. Obviously, all terms are of equal magnitude, since with an increase in the harmonic number, its amplitude decreases by n times compared to the first harmonic, while the frequency and inductive resistance increase by the same number of times. The non-sinusoidal coefficient Ku is defined as the ratio of the square root of the sum to the magnitude of the phase voltage. The disadvantage of determining Ku is some arbitrariness in the number of harmonics taken into account. If we take, for example, 9 harmonics, we get Ku = 7.22%, if 4 harmonics, then Ku = 4.81%. When the current of the primary winding of the transformer flows, the voltage amplitude on the substation tires decreases by only 1.9 V. At the same time, the coefficient of non-sinusoidality cannot be equal to 7.22%. In all literature sources, when calculating current harmonics, there are no recommendations for which harmonic numbers should be installed at the substation resonant filters. It is no coincidence that in the new GOST-2013, the value of the distortion coefficient of the sinusoidal voltage curve K(U is calculated as a percentage as a result of the i-th observation according to the formula, (that is, no calculation is made by current harmonics). In this paper, another approach is made to determine the distortion coefficient of the sinusoidal voltage curve. Rectifier installations are not sources of harmonics, but are electrical receivers with a nonlinear characteristic of electric current consumption, while the shape of the sinusoid curve of the supply voltage is distorted. This distorted sine wave is the source of the higher harmonics, which in this paper is decomposed into a Fourier series, while the calculation of the integral functions of the coefficients of the Fourier series is performed in the Mathcad program. The solution is made for three rectifier circuits. Harmonics for the installation of resonant filters are determined. As a result, a developed method is proposed for calculating the higher voltage harmonics and determining the distortion coefficient of the sinusoidal voltage curve based on the Fourier series expansion of the distorted voltage sine curve during operation of three-phase uncontrolled rectifiers.

У дисертаційній роботі здійснено комплексний аналіз особливостей функціонування ЛСЕП з врахуванням сучасних вимог концепції Smart Grid та виконано співставний аналіз методів оцінки обмінних процесів у ЛСЕП з джерелами РГ. На основі експертного аналізу виділено основні проблеми роботи ЛСЕП у вітчизняних системах електропостачання та енергозабезпечення. Розширено відому систему ПЯЕ для адекватного оцінювання рівнів ЕМС в ЛСЕП з дотриманням вимог концепції Smart Grid та оцінювання рівнів перетоків енергії на основі відомих показників. Розроблено та апробовано спеціалізований програмний модуль та нормативно-методичне забезпечення розширеного енергетичного аудиту з використанням обмінної потужності, яке дає змогу: визначити обмінну потужність та частку взаємного впливу в довільному перетині ЛСЕП з врахуванням особливостей їх конфігурації, режимів роботи окремих елементів та ЛСЕП в цілому; отримати інформацію про обмінні процеси в ЛСЕП з різним рівнем інформаційного забезпечення; адекватно враховувати особливості протікання режимів у ЛЕС, зокрема, двонаправленість потоків електроенергії та визначити реальний їх розподіл в елементах ЛСЕП.
In the dissertation the complex analysis of the peculiarities of functioning of local power supply systems (LPSS) is carried out taking into account the modern requirements of the Smart Grid concept and the comparative analysis of methods of estimation of exchange processes in LPSS with dispersed energy sources is performed. The need to extend the known LPSS system to adequately assess the EMC levels in the LPSS with the requirements of the Smart Grid concept and to estimate the energy flow rates using known indicators is justified. The analysis of exchange processes of LPSS under the influence of different types of impulse disturbances and sources of non-sinusoidal voltage and current caused by the peculiarities of modes of operation of both individual elements and the system as a whole for single and three-phase cross sections of LPSS is carried out. New relationships were obtained to evaluate the effect of non-sinusoidality and to take into account the ripple coefficients on the nature of the exchange processes. The analysis of the exchange processes in LPSS has been carried out taking into account the real characteristics of the elements with electromagnetic bonds (transformers, reactors, transmission lines, etc.) and new relationships have been obtained, which link the exchange power and the coefficients of magnetic coupling for one and three-phase LPSS operating in both sinusoidal and non-sinusoidal modes, as well as in symmetric and asymmetric modes. Regulatory and methodological support of the expanded energy audit with the use of exchange power was developed and tested. Regulatory and methodological support was used: for conducting an expanded energy audit at the enterprise of СE «Vasylkiv Leather Company» (Vasylkiv, Kyiv region); analysis of parallel operation of standby power supply systems both separately and in combination with the network used for powering server equipment of PLC «Prostonet»; was the basis for the course of lectures on discipline "Electrical Engineering Complexes", which will be taught in 2019 at Vasylkivsky College of NAU. A specialized software module and regulatory and methodological support for the extended energy audit using exchange power have been developed and tested. The proposed regulatory and methodological support makes it possible to: determine the exchange power and the proportion of mutual influence in an arbitrary intersection of LPSS, taking into account the peculiarities of their configuration, modes of operation of individual elements and LPSS as a whole; to obtain information on exchange processes in the LPSS with different levels of information support; to adequately take into account the peculiarities of the flow of modes in the LPSS, in particular, the bidirectionality of electricity flows and to determine their real distribution in the elements of LPSS.

The mode of operation of induction motors (IMs) affects their performance. In most cases, motors are optimally designed for steady state operation. When operating in other modes, additional attention is required to the problems of energy efficiency. Induction motors are the most common type of electromechanical energy converters, and a significant part of them operate under conditions of periodic changes in the load torque. The work is devoted to solving the problem of increasing the energy efficiency of asynchronous motors of electromechanical systems with a periodic load, including pumping and compressor equipment. The traditional solution to this problem for compressor equipment is the optimal design of an IM under static conditions, as well as the use of flywheels, the use of an IM with an increased slip value and controlled IM with a squirrel-cage rotor and with frequency converters. In this work, the modes of operation of asynchronous motors with periodic loading are investigated. For this, complex mathematical models are developed in the simulation system. Such models are effective in modeling taking into account periodic load changes: repetitive transient processes, their possible asymmetry and non-sinusoidality, increased influence of nonlinearity of electromagnetic parameters. In complex mathematical modeling, the mutual influence of the constituent parts of the electromechanical system is taken into account. Simulation allowed quantifying the deterioration in energy efficiency under intermittent loading, in comparison with static modes. Criteria for evaluating quasi-static modes have been developed and areas of critical decrease in efficiency have been determined. The paper proposes and demonstrates a methodology for solving this problem. For this purpose, tools have been created for the optimal design of asynchronous motors as part of electromechanical systems with periodic loading. These tools include: complex mathematical models of electromechanical systems with asynchronous motors with periodic load, mathematical tools for determining the parameters of quasi-steady-state modes, the methodology of optimal design based on the criterion of the maximum efficiency of processes under quasi-steady-state modes of operation. The possibilities, advantages and prospects of using the developed mathemati-cal apparatus for solving a number of problems to improve the efficiency of electric drives of compressor and pumping equipment are demonstrated. It is shown that by taking into account quasi-static processes, the use of complex mathematical models for the optimal design of asynchronous motors with a periodic load provides an in-crease in efficiency up to 8 ... 10%, relative to the indicators of motors that are de-signed without taking into account the quasi-static modes. The areas of intense quasi-steady-state modes are determined using the devel-oped criterion. In these areas, there is a critical decrease in efficiency compared to continuous load operation. A decrease in efficiency is associated with a decrease in the amount of kinetic energy of the rotating parts compared to the amount of electromagnetic energy. In connection with the development of a frequency-controlled asynchronous drive of mechanisms with a periodic load, the relevance of design taking into account the peculiarities of quasi-static has increased significantly. For example, a variable frequency drive of a refrigerator compressor or a heat pump can increase energy efficiency up to 40%, but at low speeds, due to a decrease in kinetic energy, the efficiency can decrease to 10 ... 15%, unless a special design methodology is applied. This problem can be solved by using the complex mathematical modeling tools developed in the article.