Vol 88, No 8 (2017)

The morphological method of synthesis of the structures of autonomous power-supply systems is presented, which is a further development of the sequential algorithms. A procedure of creating variants of the structure is given in the form of the initial information block, as well as a series of the sequentially performed operations in the formation of a tuple of electrical units with imposed restrictions being checked. The method is based on simulation of the main design rules followed by development of the design documentation. The theoretical content of the method is disclosed in the form of the initial information (axioms), rules of information processing, and logical formulas obtained as a result of applying the logical operations to the initial premises. It is recommended to use the calculation of the predicates as a mathematical basis making it possible to present the main theoretical premises of synthesis as the deductive axiomatic theory with a standard formalization. The main advantages of the proposed method are shown as specified by reduction in the time of finding of the functionally necessary structures by eliminating the need to carry out an exhaustive search for variants and using computers.

The possibility of improving the parameters of a reactive-power compensator operating in nonsinusoidal modes has been studied by means of supplementary assessment of the design power of the compensator. It is based on the decomposition of the instantaneous power into components in the modes of phase shift of current relative to supply voltage. The temporal distortion of the curve of current is also studied. To date, numerous attempts have been done to generalize the concept of reactive power to nonsinusoidal processes or to introduce other general concepts, but these attempts have not led to the creation of a generally accepted theory that would adequately reflect energetic processes in the general case in the presence of distortions of current and voltage. This paper aims to increase the efficiency of reactive power-compensator equipment for agricultural and industrial consumers operating in nonsinusoidal modes. This is achieved by the use of supplementary computational procedures in the controlling algorithm of a reactive-power compensator. In this case, the transmission-line resistance and internal resistance of the power supply are taken into account.

We determined the parameters of a current and voltage inductive transducer with a magnetic core made of a ferromagnetic material. The inductive transducer is used as a part of the block multifunctional protection of three-phase asynchronous electric motors. An equivalent circuit of a passive inductive current transducer is given. We determined the main relationships connecting the output voltage of the transducer with the measured current. Modeling of parameters was performed to expand the ranges of measured currents at a fixed frequency and in a wide frequency range. We examined the operating modes of the transducer at an idle speed, with a short circuit. The mathematical model takes into account the characteristics of the magnetic circuit, the possibility of its saturation, the higher harmonic components of the sensor output signal.

General trends in the development of electrical-distribution systems and requirements for switchgears (SGs) for midrange voltage are considered. The main advantages of conventional SGs with air insulation are indicated. Problems of transitioning to SGs with solid insulation and solid shielded insulation are considered. The volume of cells with air insulation is from three to five times greater than that of present-day SG cells with solid insulation and gas-filled cells. It is determined that application of SISS (Solid Insulated Switchgear with an grounded Shield) technology shows the greatest promise for improving SGs with solid insulation. The solid shielded insulation extends the equipment’s service life before possible repair, thus decreasing the maintenance expenses. Various manufacturers’ schematic structural variations of manufacturing of cells with solid insulation are described. The main engineering solutions of the offered designs are presented. Their advantages and disadvantageous features have been indicated. Application of the proposed system allows one to reduce the size of SGs and significantly increase security, as contacts with high-voltage are not used in a compartment SG. In addition, the moving elements of SGs under high potential require another insulation medium that will allow these elements to move, e.g., a gas, liquid, or vacuum. This means that insulation of such SG in principle is combined. Moreover, the solid insulation layer worsens heat dissipation. High electrostatic-field strengths in solid dielectric and large volumes of molded solid dielectric require special means to eliminate partial discharges. Interconnection of various elements presents a serious problem, and the elements’ boundary surface is the most weakened insulation node. For this reason, application of such elements requires elaborate engineering and special engineering solutions that improve insulation’s performance reliability and improve thermal conditions.

The results of experimental simulation of the influence of hydrometeor groups on the probability of initiation of spark channel discharges between an artificial thunderstorm cell of negative or positive polarity and the ground were presented. It has been discovered that there is a significant influence of the kind of hydrometeors and the method of their combination into a group on the initiation and stimulation of sparkdischarge propagation from an artificial thunderstorm cell. It has been revealed that injection of the groups of plate-rhombus hydrometeors sharply increases the probability of initiation of channel discharge from a negatively charged artificial cell. It has been established that volume-cylinder hydrometeors display an analogous behavior for a positively charged cell. It has been found that the simulation of accelerated formation of the spark discharge between neighboring hydrometeors in the group is a necessary condition for the initiation and stimulation of the channel-discharge propagation between the cloud and the ground. It has been revealed that a dielectric string or dielectric tape can be used for such purposes. A multifactor physical picture of hydrometeor influence on the initiation and stimulation of the spark channel discharge between an artificial thunderstorm cell and the ground has been proposed. This may result in promising methods of artificial initiation of lightning using arrays of model hydrometeors.

Results of an experimental investigation of surface barrier discharge in a three-electrode system are presented. An analysis is done of the flow intensity of charged species extracted from the plasma layer of the surface discharge by the field of high dc potential of the third electrode. A high unipolar periodic impulse voltage of 15-kHz frequency, impulse duration from 0.5 to 45 ms, and 150-ns impulse-front duration is used to form the surface discharge. A It is revealed that the voltage-impulse duration has a significant effect on the intensity of charged species flow (extracted current), the character of the influence being dependent on the voltage-impulse polarity. The influence of voltage-impulse duration on the surface-discharge current is revealed as well. Pictures of the structure of surface discharge at the rise and the fall of the voltage impulse made by means of a high-speed camera are presented. The difference of the discharge structure for different polarities of voltage impulse is revealed. It is suggested that the surface-discharge characteristics are dependent on a combination of a number of factors, such as the parameters of the impulse voltage, volume charge in the gas gap, and the charge on the barrier surface, as well as the material and surface structure of the barrier.

This overview is dedicated to issues of controlling micro hydropower plants that possess an asynchronous generator (a squirrel-cage induction motor), which converts the energy of water flow—a promising alternative source of energy—to electric energy. Modern “green electronics” allows producing cheap and reliable micro hydropower plants and ensures stability of their output parameters amidst undefined and variable load and water-flow characteristics. The modes of self-excitation with no load and under load are given. The article describes design solutions based on various topologies of power converters specially designed for solving the set control problem, and describes two topologies using a direct current link with uncontrolled and controlled rectifiers, as well as a topology with a STATCOM system. Their advantages and disadvantages are discussed, and the potential of this approach to building a micro hydropower plant based on asynchronous generators is demonstrated.

Details are investigated of the operation of an ac voltage stabilizer, a polarity-inverting pulsed converter, in the absence of input-voltage waveform distortions. The stabilizer performance was determined on the basis of a limit continuous model thereof corresponding to a vanishingly small switching period. It has been found that, in the steady-state harmonic mode, the inverting pulsed converter can be considered as an adjustable voltage source with output resistance proportional to the choke impedance. The possibility is shown of stabilizing the output voltage when the input voltage varies in a wide range without its preliminary biasing. To meet practical requirements for smoothness of output-voltage high-frequency pulsations expression have been obtained for calculating the choke inductance and condenser capacity taking into account the admissible range of choke current and output-voltage pulsations at a selected switching frequency. A technique of voltage stabilization is investigated that is based on control of the perturbation impact by way of regulating the relative time that the key stays in extreme positions, which depends on the ratio between the actual and preset voltage amplitudes. Unlike in the case of control based on deviation (a closed-loop contour), in this case ensuring stability is not a problem because the cause of the change of output voltage is dealt with rather than the consequence. It is established that, at sufficiently high structure switching frequency, control by perturbation provides sufficient accuracy of voltage stabilization because of low choke resistance.