Vol 87, No 3 (2016)

Simultaneous production of electrical and thermal energy on cogeneration plants allows to use fuel energy resources in autonomous power supply sources effectively. Application of external combustion engines, which have several advantages over other types of heat engines, is a possible way to improve cogeneration plants. Cogeneration plants based on external combustion engines represent a complex of interrelated subsystems. The main purpose of this publication is to show a possible structure of an electric subsystem. A general functional diagram of the cogeneration system and a diagram of its electrical component taking into account the features of the rotary-vane external combustion motor are presented. A permanent magnet synchronous motor and dc/dc converter are used to provide the operating modes of the energy system.

The results of theoretical studies and simulations of the effect of electromagnetic load on the magnetic leakage factor of an induction generator with a salient pole stator and rotor. A closed-form solution is obtained for this factor as a function of electromagnetic loads and teeth geometry provided the generator has an inductive load. An error of estimation of basic generator dimensions was found for the generator design for active load. It is shown that, as the linear load grows, the magnetic leakage factor goes down from its maximum, as in open circuit conditions, to the minimum value observed at a short circuit of the generator. The obtained boundary values of a linear load capacity, a magnetic induction in stator teeth, and their ratio can be used in design of a generator. Based on the theoretical study, the Arnold’s equation was updated with an additional multiplier to account for the effect of an electromagnetic load on the degree of induction modulation.

Polyfunctional electromechanical energy transformers with a ferromagnetic rotor are considered that allow full use of dissipative energy and structural, functional, and thermal integration. The combination in one machine of several technological functions is a feature of such devices. The rotor is cooled with raw material, which is processed. Air and low-melting materials with high thermal capacity and latent melting heat can act as an additional coolant. It is shown that almost all the conditional loss of active power comes from one of the components of net power, this being is heat power, which is used in the technological process. An implementation is presented of the principle of self-regulation in the division of electromagnetic power into two components of the net power: mechanical power flow and heat power. A gearless provision is discussed of low rotation speed and multiple enhancement of transformer torque based on the use of the interaction of direct and reverse fields of master and slave modules, changing the direction of rotation of the field of the slave module and duration of its action. Reverse moment is positive and leads to increased flatness of mechanical characteristics and, consequently, to increased instability of the transformer under load. The delay time of switching on the braking module needs to be chosen on the basis of the necessity of achieving a necessary result of torque of the transformer.

Electric propulsion systems have been recently used very often in various transport units. Traction electric motors can be powered, along with other consumers, from a uniform power station (UPS) of a selfsupporting unit. The application of a UPS promotes reliability and simplifies maintenance of the self-supporting unit’s electric system as the number of components of the latter is reduced. As a rule, a UPS is constructed on the basis of diesel generator sets (DGSs) of constant rotation frequency. The cost effectiveness of an electric station can be improved with the use of DGSs of varying rotation frequency. In this case, fuel economy is achieved by generating optimal shaft rotation frequency of the internal combustion engine, corresponding to the lowest brake-specific fuel consumption. The list of Russian and foreign published works dedicated to this topic is rather short, especially concerning research on the dynamic mode of work, the development of a mathematical model for the unit, and creation of a control system for a UPS with a DGS of varying rotation frequency. This article addresses the above issues, contains mathematical and simulation models of a self-supporting unit’s UPS with a DGS of varying rotation frequency, and shows the results of modeling.

A method of arc voltage gradient calculation for an electric arc furnace (EAF) is presented. The arc voltage gradient is the basic characteristic in study and simulation of an automatic power control system of an EAF. This characteristic is a strongly nonlinear multifactorial function that depends on electrical parameters of a power supply system, thermal conditions, and processes of arc heat exchange in an EAF melting bath. The method of arc voltage gradient calculation considers the relation between the electric and thermal conditions of an EAF in order to describe feasible nonlinear properties and to improve expressions for voltage and current transfer ratios as nonlinear multifactorial functions in particular. An EAF is regarded as a subject of control. Multifactorial properties are defined by the parameters of an equivalent electrical circuit of a furnace and by variable conditions of arc heat exchange in a melting chamber during steel melting. The method is effective for overcoming the uncertainty of the arc length in simulation of an EAR power controller. The unstable behavior of the furnace at a high impedance was explained using the obtained functions of the arc current and the arc voltage for various electrodes and the arc length. The minimum allowed arc current was found. The automatic power controller becomes unstable and the arc is extinguished under this value.

Transient electromagnetic processes in electrical systems present a significant risk to machines and influence the reliability of relay protection; therefore, the investigation of these processes is important. Transient modeling in transformers is presently done by construction and solution of state equations for magnetoelectrical equivalent schemes that bring together the electric and magnetic circuits of these devices, taking into account the interaction with each other. Modeling of these processes can be quite long when using modern software. An aim of the given work is development of more fast-acting method of calculation of electromagnetic transients, using a polynomial approximation of the solution, and also development of scheme model of method that creates convenience for engineers in modeling. A method of calculation of transients in electric circuits is developed on the basis of expansion of the solution of state equations in series of orthogonal Chebyshev polynomials. A scheme interpretation of the developed method is offered. It is shown that, in the special equivalent scheme, Kirchhoff’s laws apply to images of currents and magnetic fluxes as vectors containing the values of coefficients of decomposition of these values by Chebyshev polynomials. The given method allows replacement of operations with instantaneous values of currents by operations with direct currents in the presented equivalent scheme. Transient calculation via the suggested method in a single-phase transformer processor is twice as fast as with well-known methods. The presented method is especially appropriate for transient calculation in magnetoelectrical circuits, since it allows the use of voltage sources controlled by the current derivative for easy calculation of the integrals of solutions.