Laminated Stator Core Research Articles

Examination of auxiliary yoke and teeth heating technique for directly heating laminated stator cores by the secondary current heating method

Examination of auxiliary yoke and teeth heating technique for directly heating laminated stator cores by the secondary current heating method

Characterization of an Axial Flux Machine With an Additively Manufactured Stator

Axial flux machines (AFM) are promising alternatives to radial flux machines for applications that benefit from high torque density and a large diameter to axial length ratio, such as in-wheel traction motors. However, the 3D flux paths in AFM present unique challenges to manufacturing laminated stator cores. This paper positions metal additive manufacturing (AM) technology as a potential solution to manufacture unconventional electric machine components such as AFM stators by investigating novel lamination emulating geometric structures and material silicon composition as design handles. In this paper, techniques to additively manufacture soft magnetic components for rotating electric machines are reviewed, and the Hilbert pattern is identified as a promising candidate to reduce eddy-current losses in these components. To further reduce the eddy current losses, this paper investigates the use of 6.5% silicon steel, which has higher resistivity compared to conventional steel laminations. The results in this paper show that the Hilbert structure is effective in reducing the eddy current losses by 50% compared to a solid structure with 3% silicon steel, and using 6.5% silicon steel further reduces the eddy current losses by 24%. Finally, a candidate AFM stator is designed with the Hilbert pattern and fabricated additively using 6.5% silicon steel. This machine is characterized and experimentally compared with an identical axial flux machine that uses a laminated stator. The results demonstrate the potential of metal AM technology to fabricate electric machine components with eddy current losses comparable to ultra-thin gauge laminations at frequencies up to 200Hz and conventional 29Ga laminations up to 480Hz.

Reduction of Laminated Stator Core Iron Loss by Secondary Current Heating Method with Flexible Cooling Control

Reduction of Laminated Stator Core Iron Loss by Secondary Current Heating Method with Flexible Cooling Control

ПІДВИЩЕННЯ ЕФЕКТИВНОСТІ ДІАГНОСТИКИ ШИХТОВАНИХ ОСЕРДЬ ТА ВИЗНАЧЕННЯ ПОТОЧНОГО СТАНУ СИНХРОННИХ ДВИГУНІВ

Topicality. Today a large number of synchronous motors with long mean-time-between-failures operate under the conditions of industrial enterprises. They are mainly characterized by difference from the published electromagnetic parameters and degraded energy and reliability indicators, increased heating of the windings and electromagnetic vibrations, which causes a reduction in power on the shaft. Among other reasons, this is due to changes in the properties of laminated stator cores, which is the main structural element that is not replaced during repairs. Purpose. Determination of the main set of independent diagnostic parameters that would reliably distinguish the main types of defects of stator cores, first of all loosening and shorting, during their local testing using induction method and features of artificial neural networks in problems of video identification of core surface and determination of the state of synchronous motors. Metodology. The research methods of theoretical calculations of nonlinear electric circuits with non-sinusoidal power supply and methods of video identification for determination of diagnostic parameters and defects of laminated cores and the theory of neural networks in determining the current state of cores and synchronous motors in general were used during the research. Results. The obtained results specify the conditions of local testing of laminated cores from the standpoint of determining the required set of diagnostic parameters sensitive to the main types of defects, using a contactless test method, reveal the features of the use of neural network analyzers to determine the defects of the tooth zone by video identification and substantiate the principles of application of artificial neural networks in problems of predicting the states of major structural units and synchronous motors in general, due to changing properties of stator cores. Originality. The obtained results allow determining the state of the stator core and taking into account the influence of its change on the current state of synchronous motors with long or intensive operation. Practical value. The research results make it possible to assess the changes in the main parameters and characteristics of synchronous motors, determined by the actual state of the laminated stator cores and take into account their impact on energy efficiency, reliability and other operating parameters of synchronous motors. References 10, figures 7.

Homogenization and Eddy Current Loss Approximation of Soft Magnetic Composite Material for Electrical Machines

This paper investigates the soft magnetic composite (SMC) material consisting of irregular grains with induced eddy currents using finite element analysis (FEA). SMC material is made up of iron grains separated by insulation gap. The geometry of the material has been determined using an algorithm based approach and an image based approach.The effective reluctivity has been determined using two homogenization techniques. The first homogenization technique makes use of an energy formulation. The eddy current effects are evaluated taking into consideration the fill factor of the 2-D SMC material.A low frequency approximation is realized for the homogenized material. In the second technique, non-linear properties are determined using the time-stepping technique. A method has been proposed in FEA for directly including an analytical eddy current loss formula for rotating electrical machines with SMC material cores. The eddy current loss and torque have been determined for the radial flux permanent magnet synchronous machine (PMSM) having an SMC stator core and the results are then compared with the laminated stator core machine.

Characteristics Improvement of Claw-Pole Alternators for Automobile Applications by Analyzing 3-D Flux Paths in Rotors

In this article, we investigate rotor design of claw-pole alternators for automobile applications to increase output and decrease core loss. First, the electromagnetic field distribution is calculated by the three-dimensional (3-D) nonlinear time-stepping finite-element method, which considers eddy currents generated at a solid rotor core and a laminated stator core. From the results, a novel rotor design is proposed. Experimental verification is carried out to confirm the advantage of the proposed design. The mechanism of output increase and loss reduction by the proposed alternator is revealed by analyzing detailed 3-D flux paths in the rotors.

Performance Comparison Between PCB-Stator and Laminated-Core-Stator-Based Designs of Axial Flux Permanent Magnet Motors for High-Speed Low-Power Applications

Gearless and small motors operating at speeds above 10 000 rpm are finding many applications nowadays. Axial flux permanent magnet (AFPM) motors are compact and lightweight compared to radial flux motors and hence, are considered for various high-speed applications. Eliminating the stator core minimizes the associated high-frequency losses, and hence, coreless AFPM motor can be an option for high-speed applications. Furthermore, the coreless AFPM motor design minimizes the cogging torque and the axial attraction force between the stator core and the rotor magnets. However, the reduction of flux linkage in the stator windings is a challenge in coreless AFPM motor. In this article, the advantages and disadvantages of the printed circuit board (PCB)-based AFPM motor for high-speed, low-power applications are investigated. A detailed performance comparison of the PCB-based coreless AFPM motor and the AFPM motor with the laminated stator core is made. Finite-element analysis is carried out for the electromagnetic, mechanical, and thermal comparison of the two motors and the simulation results are presented. Finally, motor prototypes are fabricated and are tested to ascertain the simulation results.

Transversally Asymmetric Stiffness of Laminated Stator Core: A Solution for Noise Mitigation of Electric Machines

This paper provides electric machine designers with a stator core lamination attachment method that improves the noise and vibration performances of the machine by reducing resonance effects of critical modes. The proposed method uses welding or gluing technologies to attach the laminations together. The connections are distributed such that the core stiffness is axially, and more importantly transversally asymmetric. The novel technique leads to dampening of targeted modes and is validated experimentally. The results show great modal damping improvements up to seven times the initial value from regular cores and vibration levels reduced by 9 dB.

Robot-assisted concept for assembling form coils in laminated stator cores of large electric motors

Manufacturers of large electric motors, whether for automation or traction purposes, are facing major challenges in high-wage countries. Due to the high proportion of manual activities, a conflict between ensuring profitability and increasing variant variety arises. In order to meet the high demand for large electric motors and to maintain the value added in high-wage countries, manual manufacturing processes must be automated, at least partially. For large electric motors with form coil technology, especially the assembly into the laminated stator core represents a tedious, cost-intensive manual activity. Therefore, this paper deals with the development of a hybrid, robot-assisted assembly system for inserting form coils in laminated stator cores. The combination of manual and automated assembly activities is intended to ensure high productivity while maintaining flexibility. Before realizing such a hybrid assembly system, all process steps are simulated first. In addition, additive manufacturing is used to quickly produce and practically validate different end effector geometries. As shown by the final prototypical implementation, a major portion of the assembly of form coils can be carried out fully automatically by a dual-arm robot. Remaining challenges could be addressed by adding a vision system and thereby making use of novel machine learning techniques.

Measurements of Iron Loss in PMSM Stator Cores Based on CoFe and SiFe Lamination Sheets and Stemmed From Different Manufacturing Processes

This paper deals with the experimental study of the iron losses under real operating conditions of a permanent magnet synchronous machine. The latter is a high frequency (>1 kHz) and high power-to-weight ratio (4 kW/kg) motor intended for an aerospace application. The measurements were carried out on different laminated stator cores based on classical commercial grades, namely, the NO20 and M270-35A for the silicon–iron alloy and the Vacodur49 (0.2 mm) for the cobalt–iron alloy. The lamination sheets stemmed from different manufacturing processes: insulation (bonding varnish and C5 varnish), cutting (laser and electrical discharge machining), and thermal treatment (fully processed only and fully processed + thermal re-treatment after cutting). We measured the iron losses at no load and over a wide range of frequency (speed) until around 1400 Hz, and then we compared them to the estimations yielded by the finite-element model under ANSYS Maxwell. Hence, this allowed us to accurately assess the iron loss add-on factor ( $K_{\mathrm {add}}$ ), which takes into account the extra magnetic loss caused by a complex magneto-thermo-mechanical coupling within the ferromagnetic material. This coupling occurs during the manufacturing and the assembly phase (cutting, welding, stacking, shrink fitting, …) and also during the real running conditions of an electrical machine (elliptic field, local saturation, high frequency, and harmonics).

Evaluation of Iron Loss Distribution of Laminated Stator Core by Interlocking by means of Heat Measurement Method

Evaluation of Iron Loss Distribution of Laminated Stator Core by Interlocking by means of Heat Measurement Method

Measurement and Comparison of Iron Loss in Bonded- and Embossed-Type Segmented Stator Cores for IPMSM

According to the manufacturing process of the laminated stator core for an inserted permanent magnet synchronous motor (IPMSM), the iron loss may be different. It is because the mechanical stress imposed to electrical steel sheet is strongly dependent on the manufacturing process. This paper proposes a new iron loss measurement algorithm which utilizes the induced voltage of a search coil and exciting current. The method is effective even when the distribution of magnetic flux density is not uniform along the magnetic flux path as well as uniform. The developed iron loss measurement system is applied to bonded- and embossed-type segmented stator cores of an IPMSM, and the iron losses are quantitatively compared.

Tolerance Optimization for Assembly Systems Based on Quality Requirements Using State Space Model

The paper proposed a new systematic method to construct the functional relationship between product quality and tolerances. In the method, a unified user-defined tolerance model is designed to synthesize different kinds of tolerances using 3-D state space model; a deviation propagation model is proposed to analyze the quality-tolerance function. Particularly, the method is suitable for any kinds of tolerances and quality requirements. The method is successfully applied to the turbo-generator stator-core lamination auto-assembly project, and Monte Carlo method is used to simulate the quality performance and optimize the target tolerances.

Experimental Investigation of Contact Resistance for Water Cooled Jacket for Electric Motors and Generators

The key to the successful implementation of water jacket frame cooling in high-power electric machines, such as permanent magnet, doubly fed induction, and synchronous generators, is the contact between the laminated stator core and the frame. For improved thermal design, it is important to quantify the contact thermal resistance between lamination and frame. This paper quantitatively presents the values of conventional stator lamination and frame interface resistance through experimental results. So far, no experimental investigation has been carried out to determine this resistance. The effects of several parameters, such as surface finish, shrink fit pressures, use of thermal grease, and phase change thermal interface material on thermal contact resistance, have been experimentally investigated. The obtained values of thermal contact resistance between laminations and frame can be applied for future thermal designs of electric machines to predict accurate thermal performance.

Influence of the Electrical Steel Grade on the Performance of the Direct-Drive and Single Stage Gearbox Permanent-Magnet Machine for Wind Energy Generation, Based on an Analytical Model

The performance of a variable speed wind turbine using a direct-drive permanent-magnet synchronous generator (PMSG) as well as a PMSG with single stage planetary gearbox is compared for two grades of electric steel applied for the generator stator core lamination. A ring type, radial flux PMSG is modeled. For a fixed mechanical power input, the geometry of the generator is optimized for each turbine systems and two materials to maximize the annual efficiency of the generator. The annual efficiency is calculated based on the power curve of the generator and the probability density function of the wind speed. This function is approximated by the Weibull distribution function for a site with average wind speed of 7 m/s. For both generator systems, the annual efficiency of two optimized generators using different steel grades differs around 1%. The difference depends on a mass of active material of the generator.

Simulating Effective Engineering Elastic Constants of the Stator Core Lamination

In this paper, we study the problem of effective engineering elastic constants of stator core lamination of water turbogenerator. The three-dimensional transformations of elastic constants of composite lamina between the principal material coordinate system and the reference coordinate system are given, then the stator core lamination is modeled as the composite laminate and by utilizing the thick laminated plate model, we determine effective engineering elastic constants of the stator core lamination. Finally, a simple example is included to demonstrate the validity of the model and the programme codes.

Formaldehyde emissions in large rotating electrical machines – root cause analysis, background and prevention

Odours have been generated during commissioning and first time operation of large rotating electrical machines. These emissions were observed in machines from several manufacturers. Subsequent investigations indicated that formaldehyde was present. The main source of the emissions was located in the insulation varnish of the sheets of the stator core. In core sheet varnishes, formaldehyde containing precursors are often used as crosslinking agents. Energy input during the curing process, determines the extent of reversibly bonded formaldehyde after the cure. Weakly bonded formaldehyde is released when the coated sheets are heated during the early operation of the generator. The influence of the curing conditions on the formaldehyde emissions of stator core sheets was investigated in laboratory experiments. Experiments showed a decrease in formaldehyde emissions by increasing the energy input during the curing process. Even if the energy input was high enough to achieve the required mechanical (e.g. cross cut test), chemical (e.g. rubbing alcohol test) and electrical properties (e.g. surface resistivity), the formaldehyde release could still be reduced by further increase of the energy input. Appropriate material properties do not correlate with the amount of releasable formaldehyde in the varnish. This gives an opportunity to modify the curing to reduce or eliminate the emissions without negatively impacting the insulating properties. The influence of the chemistry of the varnishes on the formaldehyde release was also studied. Varnishes based on phenolic and melamine resins give the highest emissions, while the polyester-based varnishes showed no emissions. The temperature dependence and the kinetics of the formaldehyde release of stator core sheets are investigated in model tests. The laboratory experiments on the kinetics of the emissions showed, that at a certain temperature the majority of formaldehyde is emitted over a short time. Later emissions approach zero with continued thermal exposure. Temperature tests on stator core sheets in the range of 30–100°C showed, that at 30°C small amounts of formaldehyde are released. Interestingly, the formaldehyde emission does not increase linearly with increasing temperature, it shows a first maximum at about 60°C and a second maximum at about 100°C. This implies chemical reactions associated with definite activation energies that are required for splitting off the formaldehyde. Measures can be taken, during lamination processing, to avoid improper formaldehyde emission in large rotating electrical machines (safety measures and venting in existing machines, optimization of the curing process, development of formaldehyde free coatings for stator core laminations).

Hydro Generator High Voltage Stator Windings: Part 3 - Stator Winding Slot Support Systems

Appreciable radial electromagnetic forces are exerted on the slot sections embedded in the stator slots (Calvert, 1931). On rapidly loaded hydro generators used for peaking duty, there may be significant differences in axial and radial thermal expansion between quickly heated stator windings and the stator core (which takes a longer time to heat up), imposing significant compressive stresses on winding insulations and possibly causing insulation creep, with resulting reduction in size (Grabner & Kofler, 2001). If a stator winding is allowed to become loose within the core slots, the radial electromagnetic forces will cause winding slot section vibration. The slot radial electromagnetic forces are acting at twice the electrical frequency of the machine, so that loose winding slot sections may experience up to 8.64 million cycles of force in any day of full operation. If even the smallest winding slot section looseness is present, the slot electromagnetic forces will cause radial movement/vibration of winding at double frequency, causing rapid abrasive wear between winding insulation and stator core laminations. If corrective measures are not implemented, rapid insulation failure will result. The slot support systems consisting of slot wedging system, radial slot strips and slot section side packing are designed to prevent in-slot winding vibrations, and to ensure positive slot section grounding for prevention of in-slot partial discharges.

High frequency electromagnetic emissions of cylindrical laminated cores

PurposeThis paper aims to propose a high‐frequency (HF) model able to compute the flux density in the vicinity of the laminated stator core of an AC machine.Design/methodology/approachExperiments form the main approach. Analytical results previously obtained with a simplified rectangular laminated structure are confirmed with a standard cylindrical magnetic core.FindingsThree frequency domains are defined, depending on the skin depth relative to the thickness of the magnetic sheets. A methodological approach is proposed for each domain. For higher frequencies, the magnetic core can be considered as transparent for external field computation.Research limitations/implicationsThe HF model is valid for skin depths much lower than the thickness of the magnetic sheets.Practical implicationsThe proposed HF model provides a link between the weak field measured in the natural void existing between the stator core and the housing of large electrical machines. With such a link, it is possible to develop a new monitoring system able to detect and to localize the partial discharges in the stator winding of a large machine.Originality/valueThe low‐frequency limit of the model has been measured. It corresponds to a ratio of 1/40 between the skin depth and the magnetic sheet thickness. Therefore this model offers a new perspective for maintenance applications.

Three-dimensional analysis of tubular permanent magnet machines

This paper presents results from a three-dimensional finite element analysis of a tubular permanent magnet machine, and quantifies the influence of the laminated modules from which the stator core is assembled on the flux linkage and thrust force capability as well as on the self- and mutual inductances. The three-dimensional finite element (FE) model accounts for the nonlinear, anisotropic magnetization characteristic of the laminated stator structure, and for the voids which exist between the laminated modules. Predicted results are compared with those deduced from an axisymmetric FE model. It is shown that the emf and thrust force deduced from the three-dimensional model are significantly lower than those which are predicted from an axisymmetric field analysis, primarily as a consequence of the teeth and yoke being more highly saturated due to the presence of the voids in the laminated stator core.