Applied Mechanics and Materials Vol. 792

Abstract: At present, the control system of electric traction motors is widely used in four-regulators collected on thyristors in a bridge rectifier circuit. The feature switching processes in them are needed to introduce an artificial delay of the thyristors opening angle, which reduces the average value of the power factor up to 0.8. The article assesses the effectiveness of the combination of the rectified voltage from the point of view of increasing the energy performance of the band rectifiers for controlling the traction motor freight locomotives operating on alternating current. With this regulation the greatest effect is achieved in the first control zone, under normal conditions when the power factor is particularly low (0.2 ... 0.6). The expected improvement of the average power factor of the first zone will be about 22%, and taking into account the duration of the performance in all working areas, it should be about 5-10%

Abstract: This paper investigates a multilevel combined NPC converter for medium-and high-power energy storage systems and active power filters. The proposed multilevel NPC converter is composed of a parallel connection of multiple NPC converters using the current sharing reactors and involves the phase shifted PWM strategy for better energy quality performance. Using the switching function-based mathematical model, the proposed multilevel converter is evaluated to show the energy quality performance and fault tolerance of an energy storage system or active power filter. In addition, the switching frequency of circulating currents is analyzed to obtain its relationship with the converter parameters and maximum sharing reactor current ripple. The performance of the proposed multilevel converter is verified by simulation.

Abstract: This article is an overview of research in fault diagnosis, detection, and reconfiguration. The review particularly focuses on power electronic applications and drives. Diagnostics of systems with conventional inverter drives (CID) is considered because knowledge of fault diagnosis in CIDs can be used for application in other inverter drive topologies; therefore, several techniques of fault diagnosis and reconfiguration in CIDs are analyzed.

Abstract: The mathematical model of Francis turbine, operating at variable speed hydrounit, has created. The results of numerical modeling are fully consistent with the physical representation of the behavior of the hydraulic turbine in dynamic modes.

Abstract: The article states the description of the foreign experience in exploitation of power transformers with a core of amorphous materials and their constructive peculiarities. The technical and economic basis of their use in the distribution lines in the Russian Federation is represented. There are also the results of the substitution of conventional transformers by transformers with a core of amorphous steel.

Abstract: A subsynchronous eleсtromechanical resonance in autonomous power systems is caused by the coincidence of the natural frequency of power network and one of the natural frequencies of turbogenerator unit in the electrical power plant. The occurrence and development of subsynchronous resonance causes subsynchronous oscillations of generators rotors, which are dangerous for shaft elements of turbogenerator units. Besides that, load angle oscillations having small amplitude under frequencies of 10-15 Hz create radial vibrations in bearing supports of turbogenerator units. The vibrations cause the emergency disconnection by vibration protection. In this paper the feature of subsynchronous resonance development in autonomous power system is present in the load power uncontrolled asynchronous motors and a large amount of similar frequency-controlled asynchronous various power drives through numerical simulations are discussed.

Abstract: The article examines the methods of calculating capacitive currents in a measuring transformer based on a resistive voltage divider. The developed methods may be used to optimize the design of resistive dividers.

Abstract: The article is devoted to optimization of the reactive power sources arrangement in the industrial power grid to reduce the active power losses in transmission lines and select cross-sections of cable of the lines. To reduce the losses installing of additional reactive power sources in junctions of the grid are proposed. Thus, a problem of the optimal arrangement of the reactive power sources is appeared. This problem was solved by two stochastic optimization algorithms such as the Genetic and the Particle Swarm optimization algorithms. The cost-effectiveness of the suggested method is shown.

Abstract: The criterion of selection of external faulty states was proposed to help one to analyze generator differential protection behavior under possible faulty conditions. The use of computer modeling provides great advantages to explore protection behavior but, as a rule, transient state simulation takes much time. The approach proposed by the authors helps one to completely investigate differential protection behavior under various external fault conditions and save one’s time.

Abstract: The paper is dedicated to analyze the modern expert systems to assess the technical condition of power stations and substations high-voltage equipment. The main problems of modern expert systems and their possible solutions are determined. As the structure and their basic construction principles are considered. Also this paper proposes an algorithm for the expert system model using fuzzy inference on the basis of technical diagnostics and tests. As a case study of assessment of power transformers state based on dissolved gas analysis in the oil is presented.