Розглянуто методи оцінювання рівнів інтергармонік шляхом застосування швидкого перетворення Фур'є як безпосередньо до випадкового графіка навантаження джерела інтергармонік, так і до його кореляційної функції. Виконано оцінювання енергії дискретного спектра інтергармонік струму від такого різкозмінного навантаження, як електродугові сталеплавильні печі і зварювальні установки. Розглянуті характерні спектри інтергармонік вхідного струму безпосередніх перетворювачів частоти з однофазним виходом при лінійному і синусоїдальному законах керування. Наведено методи оцінювання інтергармонік напруги, а також методи зниження рівнів інтергармонік.

Рассмотрены методы оценки уровней интергармоник путем применения быстрого преобразования Фурье как непосредственно к случайному графику нагрузки источника интергармоник, так и к его корреляционной функции. Произведена оценка энергии дискретного спектра интергармоник тока от таких резкопеременных нагрузок, как электродуговые сталеплавильные печи и сварочные установки. Рассмотрены характерные спектры интергармоник сетевого тока непосредственных преобразователей частоты с однофазным выходом при линейном и синусоидальном законах управления. Рассмотрены методы оценки интергармоник напряжения, а также методы снижения уровней интергармоник.

The paper describes methods for estimating the levels of interharmonics by applying Fast Fourier Transform directly to a random process of the interharmonics source current and to its correlation function. The energy of the discrete current interharmonics spectrum of such quick-variable loads as electric arc furnace and welding apparatus has been calculated. The authors analyzed peculiar interharmonics spectrums of network current in the direct frequency converters with a one-phase outlet at linear and sinusoidal control function. The methods of estimating of voltage interharmonics and selection of methods of reducing the interharmonics levels have also been analyzed

Purpose. To analyze the development of the notion "Economic equivalent of reactive power" (EERP) and deals with definitions of this concept in historical perspective. Methodology. The method of researches is based on the theory of the electrical engineering at the use of methods of regulations reactive power. Findings. It is emphasized that the impact of the voltage change in the network on the alteration of resistance losses from the var flow should be taken into account while doing the corresponding mathematical derivation and introducing numerical illustration. Hence, absence of necessity to consider capacitive generation of overhead lines has been proved computationally. Peculiarities of the regulating effect of voltage related to the reactive power and EERP have been substantiated, which allows to treat them jointly within the framework of electromagnetic compatibility concept. It is stressed that in computing EERP it is reasonable to use assessed values of parameters, which is illustrated by several examples. Originality. Feasibility of using the method of incremental rates with partial derivatives has been theoretically substantiated. Incompleteness and incorrectness of the input information impact on the value of EERP have been assessed. It was proved that regulatory documents or instructions are vital to standardize recommended methods of calculations. Practical value. Approaches to project practices are also in the centre of attention. Analysis of the obtained results allowed to give a quantitative assessment to the impact of voltage on EERP, as well as to the values of minimal losses of reactive power. An approximate formula for assessing resistance of the external grid in computing EERP has been derived.

Purpose. To investigate the understudied aspects of voltage quality and electromagnetic compatibility and provide mathematical description for the analysis of voltage interharmonic components in mixed spectrum. Methodology. Methods of research are based on the theory of spectral analysis and general electrical engineering. Findings. The stress is made on the necessity to take into account the impact of interharmonics while analysing the quality of voltage in industrial power supply systems. The process of interharmonics occurrence in power supply systems is explained in terms of physics, the sources generating this kind of interference are described. Mathematical dependences that allow identifying interharmonics in the general energy of distorted spectrum are provided. The focus is placed on the feasibility of using spectral analysis in computations. We have analysed the values of error in calculations of electric power quality indexes (EPQI) and the following reasons for its occurrence: error in setting the parameters of electric equipment, their reduction, etc. It has been established that the expected error is within the range of 3 - 13 %. Originality. The Fourier integral application for the analysis of interharmonics has been theoretically substantiated. Dependences between the commutating angles of the inverter rectifiers and the level of interharmonics in the converter line current have been established. The appropriateness of preparing instructions for the application of estimating calculation methods, which are similar to those used in power engineering and other industries, has been emphasized. Practical value. Analysis of the obtained solutions allows making a quantitative estimation of levels of interharmonics and higher harmonics as the markers of the voltage quality. The approximate formula for assessing interharmonics levels while applying a linear law of invertor control has been inferred. Certain parameters used in estimating calculations are provided. It is shown that the calculated values of estimated losses in power engineering of Ukraine coincide with the results of more specific research based on factual data.