Russian Electrical Engineering

A prefabricated conductive rail joint (PCRJ) is one of the least reliable elements of a rail line. Despite the digital transformation of railway transport, one of the directions of which is the automation of monitoring the technical condition of systems and infrastructure facilities, technical diagnostics of railway transport systems are carried out by operational personnel of infrastructure distances using portable measuring instruments. The paper suggests an algorithm to monitor the transition resistance of a PCRJ, which makes it possible to automate this process. The algorithm is studied, and the methodological error of the algorithm is determined.

A combined method for the simulation of magnetic fields, characteristics, and processes in electric machines (EMs) is developed that is based on a new type of equivalent electromagnetic circuit. The new method combines calculations of the magnetic fields in local zones of an EM with numerical simulation of the discrete structure of that EM. An approach to the simulation of the 3D magnetic field of an EM whose core is characterized by axial nonuniformity is proposed

An increase in losses and electromagnetic noise of induction motors and wave overvoltages when a motor is operating from a frequency converter with pulse-width modulation of voltage due to higher temporary harmonics of voltage and current to a certain extent can be compensated by the use of combined windings, which reduce differential dissipation and inductive reactance, weakening of wave overvoltages, additional losses, and electromagnetic noise from a magnetic field’s higher spatial harmonics. The use of a combined winding with a doubled number of parallel structures when connecting the star and triangle (D connection) windings in parallel in frequency-controlled asynchronous motors makes it possible to use thinner wires and to reduce additional losses and displacement of current by higher temporary harmonics of a current. Parameters of combined windings must be selected based on a refined analysis of electromagnetic processes due to the possibility of the occurrence of equalizing currents in the circuits between the phases of different windings. An algorithm for the interaction of coupled circuit electromechanical and field electromagnetic models is proposed, which allows for refined modeling of an operation of induction motors with combined windings from a frequency converter with pulse-width modulation of voltage. When connecting the star and triangle circuits in series in a combined winding, compared to a three-phase winding, the pattern of voltage pulses, the initial and final pulse voltage distributions along the turns change, and the potential operating conditions of a winding are improved.

Basic provisions of the scientific and engineering fundamentals of the methods of an artificial initiation of the downward lightning and intracloud lightning by the model hydrometeor arrays have been formulated. The key role played by the model hydrometeor size and form on the probability of an artificial initiation of the downward lightning and intracloud lightning has been established. Volume hydrometeors of centimeter size are tailored for such goals. Dividing of the model hydrometeors on the five classes differing on the electric field amplification coefficient has been proposed. Model hydrometeors with the amplification coefficient from 5 to 19 will be the most optimal for an artificial lightning initiation. It was found that the requirements for the sizes and parameters of the model hydrometeor families and to the places of their introduction in a thundercloud will be determined in most by the effect of the earlier appearance of the avalanche corona on the hydrometeors. It discharges the nearest parts of the thunderstorm cells leading to the local decreasing of the field strength, probability of the streamer corona initiation, and its transition into the volume leader. It was determined that the combining of the model hydrometeors in the group by the dielectric string or tape and the simultaneous introduction in thundercloud of some hydrometeor arrays will significantly increase the probability of the artificial initiation of the intracloud lightning and lightning “cloud–ground,” and the successful discharging of a thundercloud. Moreover, the minimal linear sizes of separate hydrometeor groups should be more than several dozens of centimeters. Some variants of the disposition of the model hydrometeor groups in a thundercloud (near the bottom boundary of the thunderstorm cell, inside the thunderstorm cell, and in the space between the thunderstorm cells) when the most optimal conditions for the initiation of the intracloud lightning and lightning “cloud—ground” are provided, have been proposed.

To use the full potential of self-synchronized circuits (SSCs), which are often presented as being highly reliable, special methods for increasing reliability and providing fault tolerance need to be developed. They should make effective use of all the possibilities of a self-synchronized circuit structure. self-synchronized digital devices will then become a good choice in critical areas such as aerospace microelectronics. In terms of reliability, the existence of indicators and dual-rail data channels is a significant difference between SSCs and synchronous circuits. The paper is focused on “passive” fault tolerance of self-synchronized devices that are applied in hardware without permitting cessation in the course of further reconfiguration (self-repair). Variants of providing SSC fault tolerance from the probability indices of nonfailure operation and difficulty in circuit reservation and self-synchronizing (quasiand strongly self-synchronized solution) are assessed.

This paper describes a method for controlling an active voltage rectifier, which combines regulation of the dc output voltage and parametric regulation of the phase of the control signal at a given modulation depth with zero reactive current. Such control is possible in power-supply systems based on a synchronous generator with combined excitation and an active voltage rectifier at a variable speed of the electric machine shaft, in particular, in aircraft power-supply systems. At the same time, the consumption of reactive power by the synchronous generator is minimized and the energy efficiency and weight and size indicators of the entire system are increased. The active algorithm of voltage-rectifier control is implemented in a coordinate system rotating with the frequency of its input voltage, while input-voltage stabilization with a change in the generator-shaft speed is achieved by parametric control of the excitation current. The position of the generator rotor is determined by a rotor-position sensor located on its shaft. The reactive resistances of the electrical machine play the role of the buffer reactor. An algorithm for the formation of the phase of the control signal of an active voltage rectifier is proposed and studied when its rotating coordinate system is synchronized with respect to the generator voltage.

Based on the author’s direct calculation methods of power-producing processes, new quality indicators of nonsinusoidal voltages and currents in the form of integral and differential coefficients of harmonics of voltage and current have been obtained. The advisability of introducing them into the standards for the quality of the power network voltage and the consumption current, as well as also into the method for calculating of the partial participation of the consumer and the power supply system in the change in the overall quality of the electric energy has been shown.

Reduction of the load component of network power losses in a four-wire network of an alternating voltage achieved by means of ideal and real (with the help of an active filter and a device for compensating the neutral terminal current) balancing of network phase currents.

Electromagnetic shields are widely used for protecting electrical equipment and cable lines from the influence of natural and artificial electric and magnetic fields. A 3D mathematical model of a solid cylindrical shield for protection from the effect of an alternating electromagnetic field produced inside a cable has been proposed. The model has been constructed using the finite-element method in the ANSYS HFSS software. Two electromagnetic-field sources have been considered: noise in the inner conductor (cable core) and a coaxial circuit, in which the shield is an outer working conductor. The electromagnetic-field distribution over the cable is described by the Maxwell equations, which are transformed into the Helmholtz vector equation with respect to the electric-field component so that the finite-element method may be used. The electromagnetic parameters of the considered media are constant and isotropic. The shielding properties have been studied for a copper cylindrical shield in the frequency range of 1–100 MHz. As a result of the mathematical solution, the distributions of electromagnetic-field intensities in the model have been obtained. To determine the shielding properties of a cable, the transfer impedance and shielding attenuation have been used. The adequacy of the model and technique for determining the efficiency of the screening has been verified by means of comparison between the obtained data and results of the analytical model.

The basic models are discussed for estimation of the failure models of composite systems that can be put at the basis of complex analysis of the state of electrotechnical networks.