Volume 88, Nº 11 (2017)

FDM-based 3D-printing is one of the most common kinds of additive technologies. A typical printing unit consisting of a material feeding device and a printing head has a number of significant drawbacks associated with the lack of control over the basic parameters of extrusion. Basically, the only controlled parameter is the heating temperature. The article considers an alternative point of view on the problem, based on the multiagent approach and on elements of fuzzy and neural-fuzzy logic, which allows, through the introduction of additional feedbacks and simultaneous consideration of several basic parameters, to improve the quality of material extrusion, and to reduce the influence of the wire-material quality on the final 3D-printing result.

Electrostatic-field intensities have been obtained by mathematical simulations of the electric field of AS conductors of a 500-kV air line (AL) and numerical analysis based on the finite-element method using the Ansoft Maxwell software. The irregularity of the wire surface of an air line and the inhomogeneities of surface of the last cable layer have been taken into account in the study. The latter lead to a local increase in the field intensity, which, in turn, results in a loss of useful power. Phase splitting is used to decrease the electric- field intensity on air lines. Furthermore, the intensity on the individual wire decreases and, as a result, loss of power is reduced with respect to the corona discharge and line inductive reactance. Thus, to decrease loss of power of wires and to prolong the lifetime of wires, it is necessary to determine correctly the cross section of wires and kind of phase splitting. A 2D mathematical model of the AL electrostatic field has been developed that takes into account the inhomogeneity of the shape of the wire surface. The analytical solution of the initial problem has been considered, and the numerical and analytical results for a cylindrical wire surface have been compared. The fields for four cases of an AS conductor with different versions of splitting have been studied. The curves of field intensities near a conductor surface as a function of the cross section and number of wires in the AL phase have been plotted.

Noisy transient processes (TPs) in the stator windings of synchronous machines (SMs) in experiments on sudden symmetrical short circuits (SCs), field dissipation, voltage recovery, shock excitation, and other issues are especially vulnerable when they are identified by the results of bench tests using the operating standards for testing of synchronous machines. The processing methods of such transient processes according to domestic and foreign standards are overloaded with labor-intensive graphic procedures and calculations using oscillogram data. These methods to date have not made it possible to achieve the desired accuracy of TP processing due to a considerable scatter of the results of their identification. The experiment concerning a sudden SC is the main test for all transient processes, as it is asymmetric and contains the largest number of current components in the SM stator windings. Consequently, this experiment is potentially promising for finding ways to provide a high accuracy and reliability of TP identification. The other above-listed TPs are symmetrical without an asymmetric component, and so their exact identification is provided in a way similar to in the sudden SC experiment. The developed probabilistic and statistical methods (PSMs) of TP identification in many respects solve existing problems. The article presents new possibilities for the development of these methods with effective use of variational series of a random sign with the detected nucleus of effective point samples. These capabilities increase the accuracy and reliability of identification results of these TPs and reduce the labor-intensiveness of studies of a random sign in the investigated range of a TP with a transition component when processing long-term TPs of powerful SMs.

Energy-efficient control of electric drives of an overload machine and operator training for a computerized practice-machine system (CPMS) are considered. The energy consumption of an overload machine depends on the kind of control actions taken by the operator and dynamic characteristics and modes of use of the drives, which has to do with the level of the operator’s professional training. Unreasonably abrupt accelerations and hard braking increase the wear of electromechanical equipment and lead to additional electricity consumption. The energy-saving technology of overload machine control is based on presenting the operator’s work as a functionally complete set of tasks (practice exercises) formally presented as a set of tasks for optimal electric-drive control. The solution of these tasks forms a system of wanted paths and controls used as advising actions in the practice-machine system when doing a set of practices. The results of designing a computerized simulator system (CPMS) for overload machine operators are presented. The training in this system makes it possible to form skills of energy-saving control over process equipment. The operator forms his sensory motor skills in the CPMS by doing a set of practices to simulate the actual technological operations of the overload process. The CPMS is designed to accumulate, store, and process data on the acquisition of professional skills and expertise by a trainee. The structure of the skill-formation control system is given as a component of the CPMS, and its connection with the computerized simulator (overload modeling unit) is also considered.

We consider the possibility of computing the transient processes in an electric-power system of an arbitrary topology according to an algorithm taking into account the transformation coefficients of the transformers contained in the system under investigation. This problem arises when computing the dynamic modes since the structure of an electric-power system may be different at different time points. The key problem of calculating an electric-power system of an arbitrary configuration is the use in the system of elements such as transformers as the voltage levels in a part of the system are not known in advance. The problem can be solved by matching the transformer tree, which affects the voltage level of the branch for every branch of the scheme. This method is similar to the method of matching the trees of the key to every branch. When forming the matrices of the nodal conductances and driving currents, a topological list based on the principle of the element-by-element contribution is used. The main advantages of the method based on the topological list are that it does not require observation of the order of the line numeration and its high algorithmic level, which ensures minimization of the computational effort required for computerized derivation of the equations. To determine the transformation coefficient for a branch, it is necessary to pass into the depth on any of the arms of the transformer tree to the last leaf cell, subquentially multiplying the transformation coefficients of the enumerated transfomers. The complete transformer tree can be used to verify that the transformers are correctly connected to the circuit. From the point of view of trends in the development of information technologies, the approach in question allows not only automation of individual subject phases of the design, but also consideration of simulation of the interaction of electrical equipment in an electric-power system, generation of systems of scheduling, economic planning, determination of risks of equipment failure, etc.

The problem of creating timing constraints for control systems is treated. An example of a control task is presented, and the corresponding timing constraint is formulated. It has been shown that this type of constraint is not a member of the previously proposed class of linear-interval constraints. A new class of realtime constraints is proposed for control problems, which is an extension of the class of linear-interval constraints.

Structural and parameteric synthesis of an automatic control system for gas-turbine power stations complicated by the complexity, nonlinearity, and multimodality of the control object, which is both the gas-turbine power station itself and the associated electric-power system, is conducted using the simplest possible mathematical models. The development of simulation models of the electric-power systems of various structures and element compositions and analysis of the functioning of the latter when reproducing a given list of external and internal disturbances are a topical task. The conditions of a test stand offer the possibility of combining the stages of computer-aided tests, i.e., simulation of the automatic control system, and semirealistic tests, i.e., tests of mockups and experimental and pilot prototypes, using a computer model of the electric-power system. The development of program modules for simulation of the electric-power system is considered. The modules are integrated into a subsystem for testing power-generating plants. The use of the Java language facilitates the cross-platform properties and universality. The computation of the dynamic modes is represented as a sequential computation of the static modes in every sampling step. Models of the elements of the electric-power system have been developed.

It is shown that electrodynamic tests of power transformers are accompanied by the predominant consumption of a reactive power that is many times higher than the active-power consumption. A scheme of electrodynamic tests with longitudinal compensation of the reactive power using a capacitor bank is proposed. It allows a considerable reduction of the power that is consumed from the power-supply system. The parameters of the capacitor bank and the preliminary-charging voltage levels were determined that provide various current regimes for conducting both adjusting and actual short-circuiting experiments. The possibility of performing electrodynamic tests of power transformers with nominal powers of up to 630 MV A under the conditions of factory test centers using a controlled alternating-voltage source with a regulation range of 1.5–7.5 kV and a power of 22 MW was substantiated. Short-circuiting tests have a negative effect on the power-supply system because they are able to initiate a voltage dip with a duration of up to 0.2 s and even a dynamic-stability loss. As a result, the quality and reliability of electric-power supply of other consumers of the power-supply system deteriorate. The above negative consequences can be avoided and the required testing short-circuit current simultaneously provided via reduction of the total power consumed from the powersuppl system. In this study, the problem of the electromagnetic compatibility of an electrodynamic-test bench and a power-supply system is solved by compensating the reactive power during short-circuiting experiments.