Vol 88, No 5 (2017)

In the case of adjusting the average torque value of switched reluctance motors, torque ripple is most pronounced in a low-velocity mode. In this mode, the motor phase-currents are usually forcibly limited; therefore, owing to the available voltage margin, by properly selecting the positions of phase switching, one can influence the shape of the phase-currents within certain limits and, thereby, achieve a decrease in the torque ripple. This paper considers the possibilities of reducing torque ripple using very common methods for restricting the phase-current, such as voltage control and current control. Using simulation modeling in the Matlab–Simulink environment, the best combinations of control actions are found, with which torque ripple is minimal. It is shown that, by using the first method of phase-current restriction, the reduction in torque ripple under certain conditions is achieved via a forced pulling of the range of phase-current increase due to a later switching on of the phase with a simultaneous increase in the voltage across this phase. In a number of cases, the desired effect can be achieved only owing to a certain delay in the command for switching the phase off with respect to the position corresponding to a single-switching mode. For the second method of phasecurrent restriction, the best switching conditions are found for fixed levels of current restriction determined from the desired values of the average motor torque, and independent adjusting of the switch-on and switchoff positions of its phases.

A linear switched-reluctance electrical machine (LEM) intended to be used as an electric-power generator together with a free-piston internal-combustion engine (ICE) has been analyzed. Taking into account the hard service conditions of an electrical machine (EM) in close proximity to a cylinder ICE, hottemperature zones and heavy mechanical loads of the EM of the vent-inductor type have been recommended to be used. Development of a control system for this type of machine is one of the most complicated problems when developing it. It has been suggested to determine the reasonable principles and regulating algorithms of the machine that is being considered, as well as its regulation system and energy-data evaluation, on the basis of a model of the electromagnetic process. Taking into account the characteristic properties of the linear switched-reluctance machine as a modeling object, a mathematical model has been developed to solve the problems mentioned above. As stator phases have separate coil-flux guides and are not connected magnetically, the electromagnetic processes in each phase are analyzed independently. For experimental corroboration of ideas for design calculation, an experimental model of the machine has been constructed. Parameters required for modeling the characteristics’ correspondences of flux linkage and phase current’s generating force at various positions of a moving element have been determined for this machine experimentally. Performance of the linear switched reluctance electrical reciprocating machine has been analyzed with the mathematical model with moving-element movement frequencies unfeasible for study on a proving stand. Reasonable parameters of the current pulses’ phases of the machine have been determined, and its energy data have been evaluated. The obtained results have confirmed the correctness of the design approaches, choice of regulation principles, and adjustment of a linear vent-inductor electrical machine of forward and backward action and the feasibility of using it as an electric-power generator together with a free-piston ICE.

XLPE-insulated cables and wires are becoming more widespread. For this reason, it is becoming necessary to control the state of insulation over its total operating life. Online monitoring of the effects on the insulation and determination of its remaining life becomes possible using modern equipment. In this paper, a method of determining the remaining lifetime of the cross-linked polyethylene insulation of the powertransmission line is presented. An insulation-aging model developed at the previous stage of the research was used. It is proposed to control the destructive effects on the insulation and calculate the remaining life based on the obtained data. The results of the research showed that the probability of failure is subject to the normal character of distribution (Gaussian distribution) as the insulation in the process of operation is exposed to a large number of effects (partial discharges, thermal actions, effect of the environmental factors, etc.). The remaining lifetime is defined as a function of inverse failure probability. The proposed method can be used to develop a set of devices for determining the remaining life of polyethylene insulation.

A method of criterion programming has been developed for solving optimization problems in electric- power systems. The method is based on the techniques of similarity theory, criterion analysis, and geometrical programming. The main advantages of the criterion-programming method lie in using the criteria of technical and economic similarity and the possibility of solving problems of any degree of difficulty. The objective function and limitations of different types can be presented in any real form without additional transformations. This simplifies the statement of optimization problem and makes it possible to take into account more parameters to be optimized. The method of criterion programming was developed to solve problems of optimal control of electric-power system to improve the reliability and efficiency of its operation. Examples considered in the article show the fundamental interdependence between technical and economic parameters characterizing the state of electric-power systems and make it possible to reveal the main technical and economic regularities of complex electric-power systems. The possibilities of the criterion-programming method that are presented in the article expand the range of problems that can be solved by technical, economic, and mathematical analysis in electric-power engineering and can be used in other fields of science.

The fundamentals of a new theory of a two-winding autotransformer have been suggested, and a universal 4T-shaped equivalent circuit has been obtained. The circuit has a universal behavior, since it provides mapping of all the magnetic fluxes in the window and in the yoke of the autotransformer, as well as in the region between the yoke and autotransformer, tank in the case of saturation under any load. It is shown that super- and antifluxes with respect to the idle flux occur in the magnetic circuit of a short-circuited autotransformer. It has been shown that these fluxes can be much higher than the corresponding fluxes in shortcircuited transformers. It has been concluded that the autotransformer theory should be refined. It is shown that the solution of the problem requires a fundamental understanding of the operation of transformers and autotransformers.

Problems in the development of high-voltage power sources (HVPSs), magnetrons and gyrotrons, providing powerful SHF devices of two types with a continuous generating mode of SHF and periodic-pulse radiation have been considered in this paper. High-voltage power sources (HVPS) are made on the basis of a transistor–capacitor direct-voltage converter. It ensures parametric stability and safety of the HVPS–powerful SHF device system in standard operating conditions and the emergency-operation mode due to HVPS’s negative external characteristic of this type. Mathematical models of an HVPS–powerful SHF device loop describing processes at the various output-voltage pulse-forming stages of HVPS’ have been proposed and checked. An HVPS–powerful SHF device system using the control-current injection method has been analyzed. A feedforward compensator the parameters of which are determined by confinement conditions in the given ranges of output regulation limits and dynamic parameters of forming pulses has been constructed using the asymptotic-expansion method of log-magnitude curves. Taking into account the results that have been obtained, a number of HVPS devices have been produced for technological and research SHF complexes. Basic technical specifications of two developed HVPS devices have been provided as an example in this paper. The first HVPS, which has a medium-voltage power of 60 kW (25 kV/2.4 A), enables generation by an SHF radiation gyrotron of up to 20 kW of capacity in both continuous- and periodic- pulse modes with a maximum frequency of 10 Hz. The second HVPS, which has a medium-voltage power of 20 kW (5 kV/4 A), is intended for supplying power to an M-168 magnetron in the periodic-pulse generation mode of SHF radiation with a maximum frequency of 500 Hz.

Stability of any power system is a major issue for secure operation of the system. The stability of power system is concerned with the behavior of synchronous generators following disturbances. Transmission system in competitive market refers to over loading of transmission lines or transformers due to market settlement. Thus there is a need of enhancing transmission capability of the network. FACTS controllers have the capability of controlling power flow by means of controlling line parameters, voltage injection at some of the angle. In the proposed work optimal location for installation of FACTS device is obtained using NN and the amount of voltage and angle to be injected in the system using UPFC is calculated using Bees algorithm. The method is tested on IEEE 26 bus system but it is general in nature and can be applied to any power system. The results exhibit the performance of the method in maintaining the system stability and АТС enhancement.