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The paper gives a comprehensive review of lightweight materials/design of permanent-magnet-synchronous-motors and different temperature-reducing (cooling) techniques. The paper discusses and compares various simulations and performance analyses of different practically implemented solutions. Temperature and performance analyses for cooling systems using phase-changing materials, cooling jackets, and other coolants are investigated, and the use of lightweight materials and composites is compared. A discussion on numerical methods and results (finite element method analysis), in order to get a more-precise thermal mapping model for different machine structures is presented. Finally, the best temperature-reducing-cooling systems methods along with the good lightweight designs which increase the overall efficiency of the motor are discussed and commented on. [ABSTRACT FROM AUTHOR]

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There is a trend to go towards low gear-ratio or even direct-drive actuators in novel robotic applications in which high-torque density electric motors are required. The Yokeless and Segmented Armature Axial Flux Permanent Magnet Synchronous Machine is therefore considered in this work. In these applications, the motors should be capable to deliver high torque at standstill for long periods of time. This can cause overheating of the motors due to a concentration of the losses in a single phase; hence, it becomes necessary to derate the motor torque. In this work the influence of the slot/pole combination, the addition of a thermal end-winding interconnection and the equivalent thermal conductivity of the winding body on the torque performance at standstill will be studied both experimentally via temperature measurements on a prototype stator, and via a calibrated 3D thermal Finite Element model. It was found that both a good choice of the slot/pole combination and the addition of a thermal end-winding interconnection have a significant influence on the torque performance at standstill, and allow up to 8% increase in torque at standstill in comparison to a reference design. [ABSTRACT FROM AUTHOR]

Abstract The bearing voltage brings premature failure of the motor bearings in the subway traction system, which is related to the stray capacitance of the motor. Therefore, the accurate calculation of stray capacitance parameters is of great significance for predicting bearing voltage. In previous studies, stray capacitances generally were acquired from simplified model of the motor. The effect of stator end‐winding and the bearing labyrinth seal on stray capacitance was usually ignored. In this study, the stray capacitance is analysed and the finite element calculation is carried out, and the improved finite element model of motor is proposed, which includes the end‐winding treatment and the bearing labyrinth seal. Then the feasibility of the improved model is verified by the measurement, and it is found that the accurate modelling of end windings has a great influence on the capacitance, and the bearing seal capacitance cannot be ignored while it is used in the motor. Finally, the influence of labyrinth seal parameters on the bearing voltage ratio of the motor is analysed, and it is concluded that the reduction of the radial gap width or the axial gap width of labyrinth seal can effectively reduce the risk of baring current.

This article presents a novel ring-shaped hybrid fractal antenna for detection of partial discharge (PD) in inverter-fed machines. PD is known as a source of degradation and lifetime reduction in the machines winding insulation. PD activity is becoming a major concern in high performance drives, especially due to the increased use of repetitive impulse voltage with short rise-time (high dv/dt) from pulsewidth modulation-controlled inverters. The proposed hybrid fractal antenna is designed and experimentally demonstrated to show a high sensitivity in the ultrahigh-frequency bandwidth of interest for PD detection as well as an ability to discriminate PD signals from other sources of high-frequency disturbances. Additionally, the proposed PD sensing solution features a unique ring-shape geometry that facilitates its physical integration into a live machine, making it suitable as a noninvasive solution for online condition monitoring and PD detection of any inverter-fed electrical machine. [ABSTRACT FROM AUTHOR]

To achieve a carbon-neutral sustainable future, the transportation sector is experiencing quick electrification, as more and more vehicles are driven by electric motors. Electric motors are designing more and more powerful and thus pose a great increasing challenge for thermal management. In this paper, an innovative experimental study on oil spray for end winding thermal management were presented. The experimental results indicated that the oil spray cooling significantly decrease the temperature of the winding. With higher oil temperature and flow rate, better cooling performance and better temperature uniformity were achieved both for teeth and slot winding. Meanwhile, a heat transfer performance prediction model based on a fully connected artificial neural network (ANN) was developed to correlate oil spray. The model used Reynolds number and Prandtl number as inputs, and the number of neurons in hidden layer was optimized to 8. The model accurately predicts the heat transfer performance of oil spray with a correlation coefficient of 0.93. The paper is expected to be a good reference for the oil spray engineering application in e-motor cooling.

The bearing voltage brings premature failure of the motor bearings in the subway traction system, which is related to the stray capacitance of the motor. Therefore, the accurate calculation of stray capacitance parameters is of great significance for predicting bearing voltage. In previous studies, stray capacitances generally were acquired from simplified model of the motor. The effect of stator end‐winding and the bearing labyrinth seal on stray capacitance was usually ignored. In this study, the stray capacitance is analysed and the finite element calculation is carried out, and the improved finite element model of motor is proposed, which includes the end‐winding treatment and the bearing labyrinth seal. Then the feasibility of the improved model is verified by the measurement, and it is found that the accurate modelling of end windings has a great influence on the capacitance, and the bearing seal capacitance cannot be ignored while it is used in the motor. Finally, the influence of labyrinth seal parameters on the bearing voltage ratio of the motor is analysed, and it is concluded that the reduction of the radial gap width or the axial gap width of labyrinth seal can effectively reduce the risk of baring current. [ABSTRACT FROM AUTHOR]

There is a trend to go towards low gear-ratio or even direct-drive actuators in novel robotic applications in which high-torque density electric motors are required. The Yokeless and Segmented Armature Axial Flux Permanent Magnet Synchronous Machine is therefore considered in this work. In these applications, the motors should be capable to deliver high torque at standstill for long periods of time. This can cause overheating of the motors due to a concentration of the losses in a single phase; hence, it becomes necessary to derate the motor torque. In this work the influence of the slot/pole combination, the addition of a thermal end-winding interconnection and the equivalent thermal conductivity of the winding body on the torque performance at standstill will be studied both experimentally via temperature measurements on a prototype stator, and via a calibrated 3D thermal Finite Element model. It was found that both a good choice of the slot/pole combination and the addition of a thermal end-winding interconnection have a significant influence on the torque performance at standstill, and allow up to 8% increase in torque at standstill in comparison to a reference design.

Designers of the synchronous machine are required to quickly and accurately predict its characteristics. 2-D finite-element analysis (FEA) is subject to error caused by neglecting the magnetic flux in the end region composed of the end winding and the space surrounding it. For accurate prediction using 2-D FEA, it is necessary to calculate the end inductance due to the magnetic flux of the end region and to correct the armature inductance. This article proposes a modeling method, which introduces the Neumann boundary to calculate the end inductance correctly by the partial 3-D FEA simulating only the end region, and a correction method for 2-D FEA using the end inductance. Comparison reveals that the calculated characteristics obtained from the corrected 2-D FEA are in good agreement with the measured characteristics. It is demonstrated that the end inductance given by the partial 3-D FEA has reliable accuracy and the corrected 2-D FEA can achieve the same level of accuracy as full 3-D FEA in a computation time less than 1/10. [ABSTRACT FROM AUTHOR]

The uneven distribution of renewable energy supply and demand promotes the development of high-voltage direct current transmission. As the critical reactive power compensation equipment for high voltage direct current transmission, the synchronous condenser must have a strong overload capability. One of the critical factors limiting the improvement of its overload capacity is the reliability of the end winding, which depends on the magnitude of the force on end windings during dynamic large reactive power output. Therefore, this paper proposes a coupling model of transient electromagnetic force for the high voltage direct current transmission system and the end zone of the synchronous condenser. The transient response of the synchronous condenser under different fault degrees is calculated, analyzed, and verified by experiments. Based on the current response of the synchronous condenser, the transient electromagnetic force on end windings is calculated. The distribution law of the force on end windings of the synchronous condenser under different degrees of dynamic reactive power compensation process is revealed. Further, the regions on end windings with larger force during strong overload are indicated. The optimizing fixation scheme for end windings is proposed according to the distribution features of the force, which can improve the operational reliability of end windings. • Force on end windings under dynamic large reactive power output is important. • Propose transient force coupling model of end winding under large reactive power. • Reveal the law of the force on end winding during dynamic reactive power process. • Indicate the regions with a larger force under large reactive power. • Propose an optimized fixing scheme to enhance the reliability of the end windings. [ABSTRACT FROM AUTHOR]

The objective of this study is to give an understanding of how the natural frequencies and modes of the end-winding components in high-power turbogenerators can be determined. Results from an analysis of various methods are presented, and the main factors that hamper the computation of the natural frequencies with accuracy required for practical purposes are identified. Finite-element 3D modeling was performed to determine the natural frequencies of the outputs and a part of the stator bus ring. It is shown that the calculated frequencies are strongly dependent on the accuracy of modeling the boundary conditions. To improve the accuracy of numerical modeling, it is necessary to use bench and full-scale test data. [ABSTRACT FROM AUTHOR]

Generally, an electrical submersible motor generates a current with high magnitude and long interval during starting transient operation. This paper aims to analyze the electromagnetic forces on the stator end windings of an electrical submersible motor during the starting transient operation by a 3-D finite element method (FEM). A 3-D model was conducted and some complex support structures in the end regions were simplified. Then we analyzed the electromagnetic field in the end region according to the governing equations and the boundary conditions. The analysis shows that the forces on the outer layer especially in 1st and 5th coil are larger than those on the other parts. Furthermore, the force distributions on the coils in the same phase belt are different and the force distribution in each segment varies with the position and the direction. Finally, the analysis of stresses indicates that the stresses in a coil end are not small but within the yield strength of the copper coils. [ABSTRACT FROM AUTHOR]

We conducted a 3-D electromagnetic analysis coupled with a 3-D mechanical analysis to analyze end-winding vibrations and deformation in an induction machine caused by steady-state magnetic forces on the end winding. Both the analyses were based on the finite-element method. The electromagnetic analysis was used to calculate magnetic forces. During the mechanical analysis, complex support structures in the end region were simplified. We first updated and validated the mechanical model according to a modal model obtained from a modal test, and afterward analyzed deformation, vibrations, and stresses. According to the analysis, the shape of the rotary dynamic deformation of the end winding caused by dynamic forces is similar to the most excitable mode shape though the natural frequency of that mode is much higher than the excitation frequency. The static deformation caused by static forces tends to expand the coil ends outward. Under both types of deformation, the nose portion of the coil ends experiences larger displacement, but von Mises stresses are larger mainly in the knuckle portion. [ABSTRACT FROM AUTHOR]

Most electromagnetic acoustic noise of induction motors is generated when the mechanical natural frequencies of the stator coincide with or are close to the frequencies of magneto-motive forces. In order to avoid this, it is necessary to determine the motor's mechanical natural frequencies by calculation or simulation. Variation of natural frequency from yoke steel ring to motor has been studied experimentally, analytically and by structural finite-element method analysis. It thus became clear that mechanical natural frequencies increased in number and natural frequencies gradually decreased from simple yoke steel ring to motor. [ABSTRACT FROM AUTHOR]

Computational fluid-dynamics modeling has been used to investigate the cooling of the end region of a two-pole strip-wound totally enclosed fan-cooled induction motor. The modeling is validated by experimental measurements. The changes in airflow and heat transfer that each configuration gives are discussed, and recommendations are made of features that can be used to achieve lower convective thermal resistance in the end region. [ABSTRACT FROM AUTHOR]

The article presents case studies of four partial discharge (PD) activity types in hydro generator stator windings, including measurements and data analysis. The PD pattern, polarity predominance, and pulse phase analysis (PPA) in correlation with visual inspections and high-voltage testing were considered for the PD analysis.

Vibration problems of a segment of winding between two clamping plates are studied when the clamping plates, which are used to fix stator end winding, are loose. First, magnetic induction expressions of the winding while the generator was running were given by using separation of variables method. Also, the expressions of the winding electromagnetic force and dry friction force between loosing clamping plates were gotten. Secondly, a mechanical model, which was used to study nonlinear vibration problem of the winding, was set up. Fundamental resonance was analyzed by using multiple scales method, and a resonance equation of amplitude and frequency in steady state was given. Then stability, bifurcation and singularity of the steady solution were studied. Criterions of stability and transition set of the bifurcation equation were obtained. At last, through numerical calculations, resonance curves were obtained. The results are helpful for analysis and protection of generator accidents. [ABSTRACT FROM AUTHOR]

Generally, a high voltage induction motor generates a current with high magnitude and long interval during starting transient operation. This starting current causes end windings to have excessive electromagnetic force on them. This force is the source of vibration and has a negative influence on the insulation stability of end windings. Therefore, end winding design with an appropriate support system is needed. In this paper, we analyzed the distribution of electromagnetic force on the end winding part by the three-dimensional finite element method (FEM), and verified the reliability of the support structure and insulation system of end windings by stress analysis using electromagnetic force distribution. [ABSTRACT FROM AUTHOR]