Influence of saturation levels on transformer equivalent circuit model

This paper presents a modelling approach for a transformer with different saturation levels. First, the magnetic field distributions at different saturation levels in the transformer are analyzed by using numerical simulations. Then, the characteristics of the leakage magnetic flux are analyzed, and the magnetic circuits with varying leakage reluctance topologies are modeled. Finally, based on the mature duality relationship between electric and magnetic circuits, the equivalent electric circuit models are obtained. These kinds of models embody the effect of different saturation levels on the connection points of the leakage flux branches, and it can fully reflect the various working states of the transformer. The accuracy of the models is verified by comparing the circuit simulation results with those of FEM transient simulations.

Mathematical models of magnetic circuits of a magnetomodulation DC converter

Monitoring of the operation mode of autonomous power supplies with magnetically modulating DC converters and system control, differential sensitivity, improve accuracy and reliability and monitor its static characteristics in the form of a line graph.

Method for determining of the optimal thickness of sheets of magnetic cores of electrical machines by the wattmeter method

The problem of reducing magnetic losses (no-load losses) in the steel of the magnetic cores of electrical machines is investigated. The tasc of determining the optimal thickness of steel sheets of the magnetic circuit of an electric machine is considered. The criterion for optimality is the minimum power of magnetic losses in steel. Currently, this problem does not have an exact solution due to the fact that the exact ratio of the hysteresis and eddy current components of magnetic losses in steel is unknown. Analyzed the power of magnetic losses in modern electrical machines and devices, depending on the thickness of the sheets of electrical steel. A method is proposed for determining the optimal thickness of steel sheets of the magnetic circuit of an electric machine based on the wattmeter method. In the course of the experiment, two identical magnetic circuits were selected from steel sheets of different thicknesses, for which the losses in steel were measured at different frequencies of magnetization reversal and the optimal thickness of the sheets was calculated. The proposed formula for calculating the thickness of the sheets is valid for both isotropic and anisotropic steel. The proposed technique can be used for both transformers and electric motors and generators.

Stabilization of a cantilever pipe conveying fluid using electromagnetic actuators of the transformer type

The article presents an investigation of the stabilization of a cantilever pipe discharging fluid using electromagnetic actuators of the transformer type. With the flow velocity reaching a critical value, the straight equilibrium position of the pipe becomes unstable, and self-excited lateral vibrations arise. Supplying voltage to the actuators yields two opposite effects. First, each of the actuators attracts the pipe, thus introduces the effect of negative stiffness which destabilizes the middle equilibrium. Second, lateral vibrations change the gap in magnetic circuits of the actuators, which leads to oscillations of magnetic field in the cores and the electromagnetic phenomena of induction and hysteresis that impede the motion of the pipe. The combination of these two non-linear effects is ambiguous, so the problem is explored both theoretically and experimentally. First, a mathematical model of the system in form of a partial differential equation governing the dynamics of the pipe coupled with two ordinary differential equations of electro-magnetodynamics of the actuators is presented. Then, the equation of the pipe’s dynamics is discretized using the Galerkin procedure, and the resultant set of ordinary equations is solved numerically. It has been shown that the overall effect of actuators action is positive: the critical flow velocity has been increased and the amplitude of post-critical vibrations reduced. These results have been validated experimentally on a test stand.

Effect of the Temperature on the Magnetic and Energetic Properties of Soft Magnetic Composite Materials

In recent years, innovative magnetic materials have been introduced in the field of electrical machines. In the ambit of soft magnetic materials, laminated steels guarantee good robustness and high magnetic performance but, in some high-frequency applications, can be replaced by Soft Magnetic Composite (SMC) materials. SMC materials allow us to reduce the eddy currents and to design innovative 3D magnetic circuits. In general, SMCs are characterized at room temperature, but as electrical machines operate at high temperature (around 100 °C), an investigation analysis of the temperature effect has been carried out on these materials; in particular, three SMC samples with different binder percentages and process parameters have been considered for magnetic and energetic characterization.

Development of Refined Electromagnetic Models of Reciprocating Electric Generators with Permanent Magnets

The analysis of scientific papers devoted to the mathematical description of electric generators of reciprocating motion with permanent magnets demonstrated that the proposed mathematical models of this type of generators are based on the theory of magnetic circuits. Such mathematical models are based on a simplified representation of the magnetic system and the magnetic field in the form of a magnetic circuit with corresponding magnetic conductivities. However, unlike traditional rotary type electric machines, electric generators of reciprocating motion have a number of features, the omission of which in mathematical modeling causes the increase of the cost of their creation (due to the duration of the design and experimental refinement of the generators). Therefore, at the initial stages of electromagnetic calculation and solving optimization problems, it is necessary to use adequate mathematical models to improve the accuracy of calculations of the parameters of these generators. For this purpose, a mathematical model based on field theory can be used; however, its main drawback is the complexity of its application for solving optimization problems. In this regard, to improve the accuracy of calculations of the parameters of electric generators of reciprocating motion with permanent magnets, it is proposed to use refining coefficients (coefficients of scattering and buckling of the magnetic flux) in mathematical models based on the theory of magnetic circuits. The authors have developed refined electromagnetic models of electric generators of reciprocating motion with permanent magnets, which make it possible to obtain the main parameters of generators at the initial stages of electromagnetic calculation and when solving optimization problems with acceptable accuracy. A distinctive feature of the refined electromagnetic models of generators is the consideration of the scattering and buckling coefficients of the magnetic flux in the magnetic system that change during the simulation.

A Review of Techniques Used for Induction Machine Fault Modelling

Over the years, induction machines (IMs) have become key components in industry applications as mechanical power sources (working as motors) as well as electrical power sources (working as generators). Unexpected breakdowns in these components can lead to unscheduled down time and consequently to large economic losses. As breakdown of IMs for failure study is not economically feasible, several IM computer models under faulty conditions have been developed to investigate the characteristics of faulty machines and have allowed reducing the number of destructive tests. This paper provides a review of the available techniques for faulty IMs modelling. These models can be categorised as models based on electrical circuits, on magnetic circuits, models based on numerical methods and the recently proposed in the technical literature hybrid models or models based on finite element method (FEM) analytical techniques. A general description of each type of model is given with its main benefits and drawbacks in terms of accuracy, running times and ability to reproduce a given fault.