Parts Of Electrical Machines Research Articles

Comprehensive assessment of the quality of laminated core of electrical machines by the high-frequency induction-vibration method

In this work, the problem of assessing the quality of active parts of electric machines, in particular charged magnetic conductors, is considered. The essential diagnostic indicators of the actual state of the recruitment core were determined, namely specific losses during remagnetization and weakening of package pressing, which are associated with increased losses, decreased efficiency, violation of the thermal regime, etc. induction-measuring module for determining the level of inter-sheet insulation breakdown and the growth of losses in the core. It is recommended when loosening for small-sized magnetic conductors, impregnation of the weakened area with adhesive varnish and subsequent drying with a compressed core. Also, for cores of a small diameter, between the pressure washer and the extreme sheets of the core, drive textolite wedges every 2...4 teeth. When the pressing of the cores of large electric machines, in which the pressing is carried out by tension pins, is weakened, the pins are tightened. A two-dimensional field mathematical model of a charged magnetic core package was developed in order to estimate the distribution of the electromagnetic field and eddy currents and losses at different frequencies from 50 Hz to 10 kHz. It is proposed to use the analysis of the transient process when the magnetic flux changes in the magnetic circuit. To simplify the measuring scheme, it is proposed to use the process of switching the current in the excitation winding. With the help of the developed model, the calculation of transient modes was carried out on the example of the studied magnetic circuit. As an object of research, a mock-up of a stacked magnetic core was used, which is a set package of magnetic steel sheets used in magnetic cores of dry transformers of small and medium power. In order to combine the two methods, an installation was developed that allows checking the quality of pressing and the quality of inter-sheet insulation at the same time.

Research of high-frequency remagnetization model in laminated magnetic cores of electromechanical and electromagnetic energy converters

The object of research in the work is charged magnetic conductors of electric machines and transformers. Laminated magnetic wire together with windings are important active parts of electric machines that participate in electromechanical energy conversion. The reliability of the entire machine is mainly determined by the actual condition of the inter-sheet insulation. Violation of the insulation causes parasitic eddy current circuits, which increases the specific losses, and also significantly affects the additional heating of the magnet wire and winding. The normative method for determining the quality of the charged core is the assessment of specific losses at a frequency of 50 Hz and an induction of 1 T, which should not exceed 2.5–4 W/kg. To determine local damage to the core, methods of local heating and fixation of overheating sites are used, which should not exceed 45 °C compared to the main part of the magnetic core. In the work, a two-dimensional field mathematical model of a charged magnetic circuit is developed. This makes it possible to carry out electromagnetic calculations in a near-real magnetic conductor, taking into account the variability of magnetic permeability, hysteresis, and the interaction of currents in adjacent plates of the magnetic conductor with each other, the so-called "proximity effect". On the basis of the developed models, graphs of current distribution and distribution of magnetic induction in one, two and three sheets were obtained. The resulting graphs show how the effect of current displacement increases with increasing frequency, where at a frequency of 100 kHz the magnetic induction density in the middle of the sheet goes to zero. The results of the research confirm the correctness of the model development in comparison with the classical calculation models also given, which allows them to be used for further research of high-frequency processes in charged magnetic circuits of electric machines

A study of electrothermomechanical converter for technological purposes with nonlinear changes in the loading and cooling medium

Heavy temperature processes with high-temperature loads require optimisation of technological processes, ensuring high reliability and combining rotating parts of electric machines with actuators to achieve greater efficiency of electromechanical converters. The research aims to provide a theoretical justification and experimental confirmation of the effect of higher harmonics in the air gap under nonlinear changes in the temperature of the medium. The research is based on the basic principles of electrodynamics, heat and mass transfer, mathematical modelling by the finite element method, and experimental verification of multi-physical parameters. Based on the analysis of the differential equation for determining the increase in the surface temperature of a ferromagnetic rotor under conditions of nonlinear temperature changes in the environment surrounding the electromechanical converter, the regularities of the formation of the free and forced components of the instantaneous temperature values of the massive rotor are established. Depending on the mode of interaction between the load-cooling medium and the electromechanical part of the screw units, kinematic diagrams of single-mass and two-mass systems with variable or constant moments of inertia and stiffness were formed. According to the size of the electromagnetic system of the experimental sample, a mathematical model for studying thermal and electromagnetic processes was built. The regularities of the spatial distribution of the temperature of the screw electromechanical unit are determined. The spectra of higher harmonics of voltage and current in the frequency range from 0 to 50 kHz have been experimentally determined, which confirms the presence of the effect of generating higher harmonics when the temperature of the medium surrounding the rotor screw changes. The detected harmonic spectrum affects both the formation of the dynamics of the rotating system and additional thermal power while increasing the overall efficiency of the screw electromechanical converter. The practical value of the obtained results lies in the possibility of predicting the optimal indicators of interrelated electromagnetic and heat exchange processes in screw electromechanical converters for technological purposes

On the Application of Extended Grounded Slot Electrodes to Reduce Noncirculating Bearing Currents

Power-electronic-converter-induced motor bearing currents are a widespread problem in the field of electrical drives. Parasitic capacitances between the electrical machine's parts provide a path for leakage currents, which finally harm metallic ball bearings. Remembering that end-windings have a significant contribution in building up stray capacitances, a countermeasure affecting both the lamination stack and end-winding areas is needed. This article focuses on a countermeasure against the noncirculating bearing currents in the cluster of solutions at the motor side. The electrostatic shielding approach, which is a known principle to reduce capacitive couplings, is applied in electrical machines every now and then. In this article, the principle of slot-embedded grounded electrodes is extended to cover also the end-windings. Thus, the electrodes provide a better shaft-to-ground voltage mitigating effect compared to the case where electrodes are applied only in the lamination stack area. The feasibility and effectiveness of such a countermeasure are investigated. Different options in terms of scaling of both the machine size and diameter of the electrodes were analyzed and corresponding conclusions were pointed out.

Additively Manufactured Ultralight Shaped-Profile Windings for HF Electrical Machines and Weight-Sensitive Applications

Nowadays, additive manufacturing (AM) is becoming a more feasible solution for scalable electric drives compared to traditional production systems. Also, with the significantly growing automotive sector, innovation in electric machine technology is evolving rapidly. With the unmatched freedom in geometry, AM offers a great deal of flexibility in the design of electrical machine parts. Not only the passive parts can be printed such as the frame and the shaft of the electrical machine, but also active parts, such as windings, can be printed in lightweight materials such as Al–Si–Mg-based alloy. The main focus of this article is to further utilize AM in the design of electrical machine windings, with low weight and low losses especially at high-frequency (HF) operation. Aiming at HF loss reduction, different AM coils are prototyped using different materials, and their performance is compared with traditionally manufactured coils. Moreover, a new design concept of shaped-profile conductors is presented with reduced proximity effect and less impact by the cross-slot leakage flux. This design combines high electromagnetic performance and ultralightweight merits, allowing for higher power density electrical machines.

Start of the powerful synchronous motor of the rolling mill converting unit

The features of starting the powerful high-voltage grid synchronous electric motors as a part of unregulated electric drives in the metallurgical and mining industries is considered in the article. The analyzed of used in practice start modes and methods with their advantages and disadvantages. For the synchronous motor as a part of electric-machine’s converter unit a start method with an accelerating motor as a standard DC machine is proposed. The mathematical and dynamic computer models of the power supply network of an industrial enterprise and a high-voltage powerful synchronous motor are described. Suggested a recommendation option of power equipment for the proposed start scheme.

Restoring of worn-out parts of electrical machines via compositional electrochemical iron-corundum coating

Galvanic build-up of iron layer is an effective method of parts restoring during repair works. The productivity of this process is 15-20 times higher than of chroming. The high settling velocity of iron and low costs of the source material determine the economic practicability of this method. Up to 3 mm can be applied by iron plating, which is necessary in case of high parts wear.

EFFECT OF GRANULOMETRY AND OXYGEN CONTENT ON SMC MAGNETIC PROPERTIES

The interest around the adoption of Soft Magnetic Composite materials (SMC) in the realization of electric machines, or parts of electric machines, is continuously increasing. The main reason lies on the opportunity to realize magnetic circuits following a 3D design procedure, which is not allowed with the adoption of the traditional lamination sheets. This is not the only reason, as a lot of research is being carried out on the losses distribution in the magnetic material, particularly as function of the frequency. In this paper different iron powders have been analyzed to investigate the impact of the granulometry on the SMC performance; in particular the grain size and the oxygen content have been considered variable parameters. The materials, prepared, compacted and tested in our laboratories, have been characterized to obtain the magnetic characteristic and information about the iron losses.

High Cycle Fatigue Strength of Punched Thin Fe-Si Steel Sheets

Abstract Some parts of electrical machines are built from stacks of thin steel sheets, for which the coarse grain microstructure allows for minimizing magnetic losses. The fabrication process of these parts usually involves punching operations that generate important defects on the edges. Since these alterations may result in a degradation of the fatigue strength, this study aims at elaborating on a fatigue design strategy for such punched parts. To reach this objective, high cycle fatigue tests are performed on different specimens with either punched or polished edges. The results show a significant decrease of the fatigue strength for punched specimens. Scanning electron microscope observations of specimen facture surfaces reveal that defects on punched edges are at the origin of the fatigue cracks. The influence of temperature is also investigated. Fatigue tests are performed at ambient temperature (20°C) and at 180°C. According to the experimental results, no significant influence on the median fatigue strength is observed. Since crack initiation always occur on the edges, additional investigations are performed to characterize how edges are altered by punching operations. Residual stresses are determined on punched edges using x-ray diffraction techniques. As a consequence of punching, important tensile residual stresses exist along the loading direction. In association with the stress concentration caused by geometrical defects, residual stresses promote crack initiation and fast crack propagation. For a better understanding of crack initiation, edge geometries are scanned with a 3D optical profilometer, allowing us to identify the critical defect. It is found that the typical defect size is comparable to the grain size.

FINITE ELEMENT TECHNIQUE FOR SOLUTION OF THERMO-CONTACT PROBLEMS AND ITS APPLICATION IN NUMERICAL ANALYSIS OF DEVICES WORKING WITH INDUCTION HEATING

Purpose. To develop an effective approach for the numerical solution of transient thermo-contact problems and present a typical example of its utilization regarding devices working on the principle of thermoelasticity produced by induction heating and specific technological processes intended for assembly and disassembly of systems containing shrink fits. Methodology. A finite element technique for solution of 2D multiphysics (electromagnetic, thermal and structural) problems is developed, taking into account temperature dependences of material properties and continuous variations of the contact surfaces. Modeling of the contact interaction between two parts is based on the concept of a special contact finite element having no thickness. The functional for the temperature problem is supplemented with components corresponding to the thermal conductivity of this contact layer. The heat generated due to mutual sliding of both parts can also be taken into account, but the heat capacity (specific heat) of the contact layer is neglected. Using a special 1D 4-node finite elements a system of equations for the description of the thermo-contact problem is obtained. Originality. Relatively simple analytical formulae for calculation of the contact thermal resistances occurring in specific parts of electrical machines are known. The paper offers an alternative approach for the numerical solution of transient thermo-contact problems based on the concept of a special 1D contact finite element having no thickness. Results. The presented technique is applied for the computer simulation of assembly and disassembly of a shrink fit using induction heating. Conclusions regarding the choice of technological modes are made. Comparative computations for drills made from hard alloy and alloyed tool steel are carried out.

Characterization of the local electrical properties of electrical machine parts with non-trivial geometry

In electrical machines, knowing the electrical conductivity is of importance for the eddy current calculation, especially when massive iron parts are involved. Generally the conductivity is measured on samples of raw materials with simple geometries.

Cluster analysis in multithreaded design of active parts of induction motors

To speed up the process of designing active parts of induction motors, it is proposed to classify the set of basic applications into three basic groups: harmonious, torque, and torque with limited starting current. The significance of particular optimization criteria is determined for each cluster. The universal set of solutions for the subclass of IM are located inside a region delimited by solutions with the greatest significance of basic particular criteria of each of the three groups of applications. Electromagnetic and technological metrics for low-, medium-, and high-capacity induction motors and the most efficient topologies of rotor and stator slots for each of the clusters are proposed. The applicability of copper or iron machines in different areas is discussed. Cluster analysis is noted to be the next step in the transition from automated to almost automatic design of active parts of electric machines.

Active Stabilization of Axial Position of Rotor in Electric Machine

The article is devoted to the development of technical solutions centering the axis of rotation of the rotor of the electric motor during movement. Focuses on the problem of optimization of the axis of rotation of an electric machine rotor. The existing types of current unbalances of rotating part of electric machine and their causes are considered. It is specified that the methods used in practice balancing, do not meet the requirements of modern high-precision industries. A new solution to the problem of stabilization of the axial position of the rotating electric machine is suggested.

Dynamic Preisach model identification applying FEM and measured BH curve

Purpose – The purpose of this paper is to develop a viscous-type frequency dependent scalar Preisach hysteresis model and to identify the model using measured data and nonlinear numerical field analysis. The hysteresis model must be fast and well applicable in electromagnetic field simulations. Design/methodology/approach – Iron parts of electrical machines are made of non-oriented isotropic ferromagnetic materials. The finite element method (FEM) is usually applied in the numerical field analysis and design of this equipment. The scalar Preisach hysteresis model has been implemented for the simulation of static and dynamic magnetic effects inside the ferromagnetic parts of different electrical equipment. Findings – The comparison between measured and simulated data using a toroidal core shows a good agreement. A modified nonlinear version of TEAM Problem No. 30.a is also shown to test the hysteresis model in the FEM procedure. Originality/value – The dynamic model is an extension of the static one; an extra magnetic field intensity term is added to the output of the static inverse model. This is a viscosity-type dynamic model. The fixed-point method with stable scheme has been realized to take frequency dependent anomalous losses into account in FEM. This scheme can be used efficiently in the frame of any potential formulations of Maxwell's equations.

Half-Order Modeling of Saturated Synchronous Machine

Non-integer-order systems are used to model diffusion in conductive parts of electrical machines as they lead to more compact knowledge models and also to improve their precision. In this paper, a linear half-order impedance model of a ferromagnetic sheet deduced from the diffusion of magnetic field is briefly introduced. Then, from physical considerations and finite-element simulation, the nonlinear half-order impedance model of a ferromagnetic sheet is proposed, taking into account both saturation and diffusion effects. Next, it has been proved that this model can be successfully included in the equivalent circuits of a synchronous machine (SM), taking into account eddy currents in massive parts of the rotor or damper bars and of small-signal saturation. The new SM equivalent circuit is validated by stand-still frequency response tests performed on the solid salient-pole SM of 125 kVA for variable field excitation conditions. An example of the SM transfer function computation in relation to different magnetization levels indicates the usefulness of this modeling approach for robust control issues.

Improvement and Application of the Viscous-Type Frequency-Dependent Preisach Model

Iron parts of electrical machines are made of nonoriented isotropic ferromagnetic materials. The finite element method (FEM) is usually applied in the numerical field analysis and design of this equipment. The scalar Preisach hysteresis model has been implemented for the simulation of static and dynamic magnetic effects inside the ferromagnetic parts of motors. The dynamic model is an extension of the static one; an extra magnetic field intensity term is added to the output of the static inverse model. This is a viscosity-type dynamic model. The fixed point method with stable scheme has been realized to take frequency-dependent anomalous losses into account in FEM. This scheme can be used efficiently in the frame of any potential formulations of Maxwell's equations. The comparison between measured and simulated data using a toroidal core shows a good agreement. A modified nonlinear version of T.E.A.M. Problem No. 30.a is also shown to test the hysteresis model in the FEM procedure.

An Observation of Body Force Distributions in Electric Machines

It is required to calculate the electromagnetic forces at the distributed parts of electric machines for the prediction of performance. In this paper, the body force distribution of electric machines such as surface permanent magnet and interior permanent magnet is presented and discussed for the first time using the recently developed body force calculation methods which are based on the virtual air gap scheme. The torque contribution of the body force is investigated according to radial and circumferential directions

Analysis Of Electrical – Thermal Coupling Of Induction Machine

The interaction of the Electrical and mechanical parts of Electrical machines gives rise to the heating of the machine's constituent parts. This consequently leads to an increase in temperature which if not properly monitored may lead to the breakdown of the machine. This paper therefore presents the Electrical and thermal coupling of induction machine in order to study its mechanical and electrical transient behaviours at run-up condition. The analysis of the coupled system is represented in state variable form with currents and temperatures of the machine parts as its variables. The proposed electrical - thermal coupling of induction machine is simulated. KEY WORDS: Thermal Network, Simulation, Induction machine, Mechanical model, Lumped parameter. Global Journal of Engineering Research Vol.3(1&2) 2004: 21-37

A novel approach for temperature estimation in squirrel-cage induction motor without sensors

In this paper, the authors present a coupled thermal and electromechanical model for squirrel-cage induction motor simulation and analyses. The effect of iron saturation, rotor parameter variation due to current displacement (skin-effect) and temperature variations of both stator and rotor resistances are taking into account simultaneously. A new device for the temperature measurement in the stationary as well as rotating parts of electric machines is built. The unique construction of the device for continuous rotor temperature monitoring is briefly described. This device is a part of a complete acquisition system, which is used for precise testing and investigating of a coupled thermal and electromechanical phenomena. An original thermal observer based on the direct stator temperature measurement under normal running condition with no additional sensors is proposed.

Nonlinear finite element solution of electrical machines under no-load and full-load conditions

The magnetic field distribution in saturable iron parts of electrical machines is defined by a quasi-Poisson equation. The solution to this equation is obtained by minimizing an energy functional by means of trial functions defined in triangular subregions of the two-dimensional field region. This method is applied to an electrical machine for predicting its no-load and on-load performance. Good agreement is obtained between estimated values and test results. Under load conditions, since the pole axis is not an axis of symmetry, a new boundary condition is introduced. Graphical plots of the flux distribution for the machine under different operating conditions are shown.