Electrical Power Engineering Intro 8 (original) (raw)
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International Journal of Electrical Engineering Education, 2004
Conditions resulting in a unique solution of Maxwell's equations are investigated. For this purpose, time-varying electromagnetic fields in media exhibiting a linearized form of hysteresis are considered. The treatment is an extension of the uniqueness theorem for electromagnetic fields in hysteresis-free media. The major conclusions are that there is no initial condition for fields in lossy regions, however, boundary conditions must be satisfied for all values of time. The treatment presented may be useful to students preparing for a masters degree or final year bachelor's degree.
C C I I NUMERICAL CALCULATION OF MAGNETIC DISSIPATION AND FORCES ON COIL IN POWER TRANFORMERS
INTRODUCTION Numerical methods of determining the magnetic dissipation and forces for different positions and shapes of windings and magnetic core are more and more used by the constructors in the transformers manufacture. Special attention during the calculation and analysis of the magnetic dissipation has to be dedicated to the non-linearity of the transformer magnetic circle (µ=f(B)). Before, these weaknesses, exercised at resolving the Poisson’s differential equation by analytical methods, were avoided by utilization of the graphical methods based on the orthogonal characteristics of lines of field and lines of the constant potentials. Numerical calculation of the transformer magnetic field was done by using the method of finite elements. This method enables determination of allocation of static or time changing field in linear or non-linear, isotropic or anti-isotropic type of material with electric current or permanent magnetic stimulus. The finite elements analysis is divided on pre-processing, resolution and post-processing phases. A result accuracy of magnetic field depends on modeling and discretization of the problem, determined edge conditions and parameters of the materials used. It is hard to find general methodology for discretization and determining the edge conditions. With the application of the finite elements method, the field function, described by differential equation, can not be directly determined from the differential equation, but it provides data on minimization of an appropriate function. From the numerical calculation of magnetic field, the dissipation inductivity is determined by the application of the energy method and linked fluxes method. For calculation of electromagnetic forces the energetic method was used, by which, basing on small shifts of body on which the forces exercise along directions of coordinate axes, the appropriate increase of magnetic energy or co-energy of nonlinear magnetic system is calculated.
Evaluation of forces in magnetic materials by means of energy and co-energy methods
The European Physical Journal B - Condensed Matter, 2002
The evaluation of the total force of magnetic origin acting upon a body in a stationary magnetic field is often carried out using the so-called magnetic energy (or co-energy) method, which is based on the derivation of the magnetic energy (or co-energy) with respect to a virtual rigid displacement of the considered body. The application of this method is usually justified by resorting to the energy conservation principle, written in terms both of electrical and of mechanical quantities. In this paper we shall reexamine the whole matter in the context of classical thermodynamics, in order to obtain a more comprehensive and general proof of the validity of the energy (or co-energy) approach and to point out its limitations. Two typical configurations will be discussed; in the first one, the field sources are represented by conducting bodies carrying free currents, whereas in the second one a permanent magnet creates the driving field. All magnetic materials are assumed to be non-hysteretic and permanent magnets are represented by means of the well-known linear model in the second quadrant of the (B,H) plane.
On the Importance of Incorporating Iron Losses in the Magnetic Field Solution of Electrical Machines
IEEE Transactions on Magnetics, 2000
This paper studies the effects of iron losses on the magnetic field solution and evaluates their impacts on the overall performance of electrical machines. Because of the complications associated with the inclusion of iron losses into the magnetic field solution, the losses are usually omitted from the finite-element (FE) analysis while they are estimated in a post-processing stage. We conducted a comprehensive FE analysis to study how the iron losses affect the accuracy of the magnetic field solution and what kind of role the losses play in defining the behavior and operation of electrical machines. We found that the inclusion of iron losses in the FE field solution of rotating electrical machines is primarily important for predicting iron losses accurately. Other electrical and mechanical quantities, including input power, supply current, power factor, copper losses, and rotational speed are only slightly affected by iron losses. Therefore, we have proposed an empirical equation that can be used to correct the iron losses that are calculated from the post-processing of the FE solution.
Coupled Electromagnetic and Thermal Analysis of Electric Machines
MATEC Web of Conferences, 2020
This paper deals with the design process of electric machines, proposing a design flowchart which couples the electromagnetic and thermal models of the machine, assisted by finite element techniques. The optimization of an electrical machine, in terms of the energy efficiency and cost reduction requirements, benefits from the coupling design of the electromagnetic and thermal models. It allows the maximization of the current density and, consequently, the torque/power density within thermal limits of the active materials. The proposed coupled electromagneticthermal analysis is demonstrated using a single-phase transformer of 1 kVA. Finite element analysis is carried out via ANSYS Workbench, using Maxwell 3D for the electromagnetic design, with resistive and iron losses directly coupled to a steady-state thermal simulation, in order to determine the temperature rise which, in turn, returns to electromagnetic model for material properties update.