The article is devoted to the study of electromagnetic moment pulsations that occur in slotless magnetoelectric synchronous machines. The influence of the width of the magnets and the shape of the stator MMF distribution on the level of electromagnetic torque pulsations is shown.
A classical pattern of a multistage electromagnetic accelerator for hurling massive ferromagnetic projectiles by means of a unidirectional traveling magnetic field is considered. An approach to the development of a simulation dynamic model of the accelerator is presented. The model is based on differential equations reflecting the dynamic state of the electromechanical accelerator system, the solution for which is obtained by structural simulation methods with the use of the MATLAB/Simulink software package. A control method is proposed to provide an increase in the final velocity of the ferromagnetic projectile. The effect of the number of the sequential stages of the electromagnetic accelerator exerted on the final projectile velocity is established, and a quantitative assessment thereof is presented. By using the example of a six-stage electromagnetic accelerator, time diagrams that reflect the dynamic characteristics of a variant of the simulation model are obtained.
In this paper, we consider methods for calculating nonnominal operating modes of induction motors used in wells with individual characteristics. The results of research aimed at obtaining the coefficients necessary for further creation of a method for calculating nonnominal operating modes are presented.
An autonomous multilevel single-phase inverter with no applied pulse-width modulation (PWM) and capacitive voltage dividers, the output voltage curve of which is close to a sine-wave shape and corresponds to the contemporary standards of electrical energy quality for 0.38-kV networks is considered. As compared with inverters with the use of PWM, the proposed inverter, owing to the use of low switching frequencies for power semiconductors at a level of the industrial frequency of 50 Hz and due to the optimal use of different-level amplitudes, should not generate significant electromagnetic interference and not cause accelerated wear in the insulation of connected equipment. Studies that have been performed with mathematical and physical models have demonstrated the potentiality of obtaining a voltage with a permissible harmonic coefficient at a level of KHU amounting to about 6.36% for 0.38-kV networks with the use of a three-level autonomous inverter constructed based on a three-core magnetic circuit of the transformer with a passive LC filter containing a sequential resonant circuit.
A simulation dynamic model is proposed for a pulsed electromagnetic drive with striker position control actualized by means of structural simulation provided by the MATLAB/Simulink software package with the use of numerical methods. The model takes into account the nonlinear properties of the magnetic materials under application, as well as the scattering fluxes and energy losses in the electromechanical system of the electromagnetic drive. The use of the model for analysis of electromechanical processes and adjustments in choosing main structural elements makes it possible to improve the design quality of single-winding electromagnetic drives with an elastic reverse of the striker. A quantitative estimate of the simulation results is presented. It has been noted that it is worthwhile to control the kinetic energy at the output of a pulsed electromagnetic drive in the course of the working stroke of the striker.
This work involves an efficient approach for the modeling and discrimination of the stator asymmetries and magnetic saturation in the self-excited induction generators. For this purpose, an improved model considering magnetic saturation has been developed for the self-excited induction generators operating under asymmetrical load conditions. Magnetic saturation must be considered for the modeling and analysis of the self-excited induction generators. This is because linear modeling with fixed parameters never makes it possible to analyze the performances of such machines. Due to fact that the magnetic saturation and stator asymmetries both cases generate similar harmonic components through the stator voltages and currents, we have to elaborate an improved model to evaluate the electromagnetic performances and to clearly discriminate the stator asymmetries and magnetic saturation. The contribution of this work is that a state model has been developed considering the increase of the common point voltage during asymmetrical conditions and the derivation of the machine inductances due to magnetic saturation. Various electromagnetic characteristics have been extracted such as stator voltages, currents and common point voltage. It will be deduced that the common point voltage can be considered as an interesting signal for the discrimination of the stator asymmetries and magnetic saturation. The concordance between simulation and experimental results shows the consistency of this approach for the modeling and discrimination of the stator asymmetries and magnetic saturation in the self-excited induction generators.
Results of physical simulation of the impact of lightning electromagnetic radiation on fiber-optic communication lines performed using a lightning current generator are presented. In the course of simulation of the lightning current, the first component of the lightning current was formed: a current pulse of the first reverse discharge with an amplitude of more than 190 kA and a front duration of 4 μs. A completely dielectric fiber-optic cable was located at different distances from the discharge gap or outside the screened room in which the lightning current generator was located. Linearly polarized radiation was used as a signal transmitted via a fiber-optic cable. The rotation of the plane of polarization was recorded by measuring the power of the transmitted signal. A rapid change in the state of polarization of the transmitted signal was revealed at the moment of discharge of the lightning-current generator. A surge in the optical radiation power was observed for a cable laid close to and at a distance from the discharge gap. The power of optical radiation transmitted through a cable laid outside the screened room practically did not change at the time of discharge. A hypothesis has been made that the electrical component of the electromagnetic field induced by a lightning discharge makes a more significant contribution to the rotation of the polarization plane than does magnetic component.
The results of studies of the effect of specific surface conductivity γS on the accumulation and dissipation of static electricity (SE) charges on the surface of polymer dielectrics are presented. Samples with a thickness of 1–5 mm with a specific volumetric conductivity of γV60 ≤ 10—12 Ω–1 m–1 were selected for research. It has been found that such dielectrics are characterized by the absence of a steady-state mode after voltage application, since the current flowing through the volume of the dielectric is constantly decreasing. The dependence of γS on the tangential component of constant electric field strength γS = f(Eτ) in the range Eτ = 5 × 102–5 × 105 V/m is studied. It has been found that, for dielectrics with a basic surface conductivity of γS0 < 10–12 Ω–1, a nonlinear dependence of γS = f(Eτ) is observed, and this nonlinearity increases with a decrease in γS0. It has also been found that a more pronounced nonlinearity γS = f(Eτ) is characteristic of hydrophobic dielectrics. Mathematical modeling of the accumulation and dissipation of SE charges is performed without and with taking into account the nonlinear dependence of γS = f(Eτ). It is concluded that, for dielectrics with γV60 ≤ 10–12 Ω–1 m–1, only surface conductivity can be taken into account; moreover, while γS = const for hydrophilic dielectrics, for hydrophobic dielectrics it is necessary to take into account the nonlinear dependence γS = f(Eτ).
The main structural and technological factors affecting the electrical strength of composite polymeric insulation are determined. The effect of the composite insulation structure on the abilities to provide a high level of electrical insulation characteristics is shown, and the main ways to optimize the insulation structure are considered. An analysis of the potentialities and tools providing an increase in the electrical strength of polymeric insulation has been performed taking into account available theoretical and experimental studies. The main ways to provide an increase in the electrical strength of polymeric composite insulation in the junction zone of polymers and circumfused insulating or metal elements have been revealed. Key ways to increase the heat resistance and thermal conductivity of high-voltage polymeric insulation have been formulated and grounded.
The paper is devoted to an overview of the development of insulating materials and media used in high-voltage equipment over the past 150 years. The transition from traditional dielectrics such as air, porcelain, and glass to modern developments based on polymers and polymeric composites is considered. The increase in the use of synthetic liquids such as silicone and specialty oils is discussed, and the emergence of alternatives, such as liquid nitrogen for technological applications of superconductivity, is considered. Special attention is paid to the use of different gases, for example, fluoronitriles and ketones at different pressure values as an alternative to air and gas for gas insulation of high-voltage equipment.
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