Vol 87, No 11 (2016)

Mathematical modeling of heat transfer processes inside a cable channel taking into account natural convection and radiation between the cable surface and tube and the loss in shields was carried out. An underground cable channel consisting of eight lines with a voltage of 6 kV and six lines with a voltage of 35 kV was investigated. The conductor section is 150 mm². Cables of APvVng-LS brand were placed in a triangle inside polyethylene tubes. The patterns of temperature fields obtained under variance of different various factors were determined, the permissible currents were calculated, and the optimal circuits of connection of cable lines depending on the selected criterion were proposed. The two-dimensional nonstationary problem of complicated heat and mass transfer and heat conductivity inside the underground cable channel was solved by the finite elements method using the ANSYS software package. The range of permissible operating currents depending on the location of cable lines and priority of their connection was determined. The effect of the temperature of the environment on the permissible current was considered. The optimal ranges of thermal permissible currents taking into account the shield loss were calculated. The optimal connection circuits of the cable lines depending on the problem being solved were obtained. An estimation of transferred power for every considered connection method is presented. Conclusions for practical application of the method of connection of the cable line were drawn. The fields of application of this mathematical model were proposed.

The use of adaptive control of gas turbine units (GTUs) intended for the drives of electric generators in electric power stations operating in the offline mode is considered. The requirements for electric power quality indices for such power plants and a standard control system for GTUs, which it is proposed to supplement with a special adaptation module, are discussed. The desired behavior of control system is set using the reference model. The reference model is created based on the simplified nonlinear model of a GTU. The structure of the reference model is chosen based on the physical principles of energy conversion in the GTU. The coefficients of the model and the nonlinear diagrams of change of the model parameters are determined by the results of experiments on a real GTU. The new adaptive control system is compared with the standard GTU control system. For this purpose, the diagram of load change is set and the transient processes at load changes are analyzed.

The software implementation of the node-voltage equations for calculating the parameters of electric-power systems on the basis of the topological list is considered. Of the well-known modifications of the node-voltage method, it is proposed to use the equations for node voltages in the form of a current balance when specifying a constant-conductivity load. To eliminate the harmonic components during calculations, the equation for each element of the electric-power system is represented in the Park–Gorev axes. When forming the matrices of the nodal conductivities and specifying currents, a topological list that is based on the principle of piecemeal contributions is used. The key advantages of the method that is based on the topological list are that it is unnecessary to observe the order of numbering rows and that this method is highly algorithmic, thus providing the minimization of the computational efforts in compiling equations on a computer. The essence of the piecemeal-contribution principle lies in the successive formation of matrix coefficients, as row-by-row processing of the topological list is performed. An algorithm for the formation of equations according to the node-voltage method using the topological list in the form of a block diagram is presented. Calculation using the node-voltage method on the basis of the topological list is an independent task, as well as representing a component of more complex types of calculations, such as optimization of the normal modes, stability analysis, reliability assessment, etc. The interrelations between individual components of the process of solving the problem of calculating stationary and quasi-stationary operating modes of the electric-power system with respect to input and output information are shown. The formation of the equations of the structural elements in stationary and quasi-stationary modes of the electric-power system of a factory is based on the linearization of the initial node-voltage equations.

The interdependence of loss in an alternating-current converter-fed motor with a frequency and level of supply voltage for an alternating-current converter-fed reciprocating action motor is shown in this work. The equations for efficiency of a supply cable with a length up to 3 km are presented. The influence of a step-down transformer and frequency converter on the losses was considered. It is determined that the line losses are commensurable with the motor losses. In this case, the line efficiency can be matched with the load and the efficiency reduced up to 50%. In addition, the transmission of practically maximum power to the motor is provided. The possibility of using the line losses for warming up a liquid is shown. In the case of a need to warm up a liquid warming, the current of the motor should have the rated value and the voltage frequency should be minimum. To decrease the losses in the line and in the motor, it is necessary to increase the voltage frequency to the rated value. Thus, it is determined whether the voltage frequency should be reduced or increased at the rated motor current. The expressions to calculate the necessary number of the modules of motor at the set well depth are presented. It is shown that, for depths 1, 2, and 3 km, it is possible to use the standard voltages of 380, 660, and 1000 V, respectively. With increasing well depth, the number of motor modules rises, which leads an increase in the voltage proportional to the well depth. An interdependence of the supply voltage of several motor modules with a well depth up to 10 km is obtained.

The structure of series reactive power hybrid source designed for current regulation in a transmission line is presented. The device also allows effective limiting of the rise rate of the short circuit current providing equipment safety. The following two variants for devices development are considered: based on a three-phase thyristor or on a single-phase bridge. Description of devices operational principles are given, and operating modes of the reactive power sources are determined. Simulation modeling of devices was carried out on the basis of Matlab/Simulink. As a result of simulation, research on the transmission current harmonic composition and the current regulating limits as a function of the passive filter contour parameters were carried out. The main parameters of the device elements and typical power of transformers for both variants of the reactive power sources were determined.

This article presents the results of designing a high-velocity permanent magnet turbo generator. The strength of the rotor magnet system is ensured, losses in the magnet body minimized, and magnets heated up using a sleeve (shroud) made from a special alloy. The losses in the stator core steel and the saturation factor are minimized using the 49 KF material. The generator design includes a gasdynamic stator suspension. The generator has a two-loop cooling system that makes use of the gas turbine actuating medium (He circulating at P = 20 Bar and T = 360 K). Some of the He is delivered to the heat exchanger at P = 20 Bar and T = 650 K, where its temperature is decreased to 360 K; the gas then is delivered to the loops to cool the active parts of the generator. The temperature distribution in the active zone of the generator cooled by He is calculated.