Analysis of exact and approximating dependences of active resistance of a conductor on the current frequency based on the influence of skin effect

The operation of semiconductor power converters, which are part of tractionsubstations, frequency-controlled electric drives and other powerful nonlinear loads, cause asignificant emission of higher harmonics of currents to electrical networks. Higher harmonics ofcurrents in electrical networks cause a complex negative effect on the energy efficiency of thenetwork. The increase in power losses in the active resistance under the action of higher harmonicsis due to the increase in the root mean square value of the current and the action of the skin effect.Analytical expressions describing the dependence of the active and impedance of the electricnetwork on the current frequency are determined. Based on them, analytical expressions are obtainedfor the calculation of additional power losses under the action of higher harmonics of currents, whichare due to the skin effect. The dependences of the active resistance of the electric network on thefrequency of higher harmonics are determined on the basis of Bessel equations. The analysis of convergence of the received equations with the data of the international standard IEC 60287-1-1 iscarried out. For the high-frequency zone, simplified approximating dependences are given, whichdetermine the parabolic dependence of the active resistance on the frequency. Simplifiedapproximating dependences of active resistance on the frequency of higher harmonics are obtainedfor engineering calculations. The obtained equations can be used to determine additional powerlosses in the active supports of electrical networks, windings of electric machines, high-frequencytransformers from higher harmonics of currents at different nonlinear loads. In addition, the obtainedexpressions can be used to justify the use of filter-compensating devices.

TECHNICAL MEANS FOR SUPPRESSION OF RESONANCE PHENOMENA IN ELECTRICAL NETWORKS

The self-excitation phenomenon of generators connected to an unloaded power line is considered. Accordingly, the selected values of the conductivity of the controlled shunt reactors, following the control range (especially in the overload mode), avoid the occurrence of self-excitation of the generators. The physical analysis of the processes occurring at self-excitation of the synchronous generator is given, and the calculated models are developed. It is established that in the case of artificial support along the entire length of the voltage line at the nominal value using controlled compensating devices, the transmission will have properties characteristic of relatively short lines (up to 500 km) regardless of its geometric length. It is determined that the length of the line section at the ends of which the DC voltage is maintained is much less than 500 km. Therefore, less than the natural voltage along the section length will exceed the nominal value at the transmitted power, and the line will have excess reactive power. Consumption in intermediate compensation devices (compensation current must be inductive). Ref.8, fig. 4, tables 4.

Customer compensating device placement control in energy systems

The choice of the installation site for compensating devices is determined by various factors that should be taken into account when performing calculations. The location of reactive power compensation devices is determined by the results of mathematical modeling and the optimal operating mode of individual sections of electrical networks. The paper presents the results of modeling, considers the uncertainties encountered when solving the problem of placing compensating devices.

Analysis of compensating devices efficiency in ac traction power supply systems

The article describes the main methods of reactive power compensation used in 27.5 kV AC traction power supply systems on the railways of the Russian Federation. The cases of installation of the longitudinal and transverse capacitive compensation devices at traction substation and sectiolizing post are considered in this paper. Based on experimental data their effectiveness has been analysed by comparing the main parameters of the traction power supply system before and after the installation of the compensating devices. The main effect in terms of power consumption reduction is achieved through application of reactive power cross-compensation devices. The results of the analysis show that the total electricity consumption in the researched area decreased by 23 % and the proportion of higher harmonic elements of voltage decreased by 15 %.

The electric substations compensating devices’ distribution optimization

The article discusses methods for calculating electrical networks when choosing the consumer compensating devices’ location. The main network and calculation module of a complex network is analyzed. The mathematical support of the reactive power factor compensation (PFC) problem is described in regional power systems, the areas of application of individual models are substantiated, and the results of the practical use of the corresponding calculation results are analyzed.

Expert system application for reactive power compensation in isolated electric power systems

Effective electricity use can be an option which enables to achieve significant economy while generating and transmitting of electricity. One of the most important things is to improve the electricity quality through reactive power correction up to optimum values. The current article presents the solution to compensate the reactive power in the distribution networks, in GornoBadakhshan Autonomous Oblast (GBAO) with the use of the advanced technologies based on the data collection within real time. The article describes the methodology of fuzzy logic application and bio-heuristic algorithms for the suggested solution effectiveness to be determined. Fuzzy logic application to specify the node priority for compensating devices based on the linguistic matrix power loss and voltage gives the possibility to the expert to take appropriate solutions for compensating devices installation location to be determined. The appropriate (correct) determination of the compensating devices installation location in the electric power system ensures the effective regulation of the reactive power with the least economic costs. Optimization problems related to the active power loss minimization are solved as well as the cost minimization with compensating devices to ensure the values tan(φ) not exceeding 0.35 through reducing multi-objective problem to the single-objective one using linear convolution.

An optimization-based design approach for a novel self-adjuster using shear thickening fluid

Recently, the increasingly strict safety and emission regulations in the automotive industry drove the interest towards automatic length compensating devices, e.g., hydraulic lash adjusters (lower emission) and slack adjuster in brake systems (faster brake response). These devices have two crucial requirements: (a) be stiff during high load, while (b) be flexible in the released state to compensate for environmental effects such as wear and temperature difference. This study aims to use the advantageous properties of shear thickening fluids to develop a less complicated, cost-efficient design. The proposed design is modeled by a system of ordinary differential equations in which the effect of the non-Newtonian fluid flow is taken into account with a novel, simplified, semi-analytical flow rate-pressure drop relationship suitable for handling arbitrary rheology. The adjuster’s dimensions are determined with a multi-objective genetic algorithm based on the coupled solid-fluid mechanical model for six different shear thickening rheologies. The accuracy of the simplified flow model is verified by means of steady-state and transient CFD simulations for the optimal candidates. We have found that the dominating parameters of such devices are (a) the shear thickening region of the fluid rheology and (b) the gap sizes, while the piston diameters and the zero viscosity or the critical shear rate of the fluid have less effect. Based on the results, we give guidelines to design similar-length compensating devices.

Unfavourable Reactive Power in a Rolling Mill

The electrical consumption of the rolling mill is usually very high, above 10MW, and significantly changes during the rolling process. The rolling mill drives consume not only active but also reactive inductive power. This reactive consumption is directly compensated in the rolling mill. In order to achieve feasible energy efficiency, it is necessary to maintain balance between the instantaneous reactive inductive consumption of the drives and the instantaneous capacitive consumption of the compensating devices. The results of the consumption measurements in the real working rolling mill are presented and discussed in this paper.