Saturation Effects on Unbalanced Magnetic Pull in a Hydroelectric Generator With an Eccentric Rotor

We report an investigation of saturation effects on the unbalanced magnetic pull in a hydroelectric generator with 20% static eccentricity. We determine the magnetic pull force by the finite-element method in parallel with a simple analytical model for various no-load voltages and loads. Saturation significantly affects the magnitude of the unbalanced magnetic pull for high voltages and large loads.     

Comparison of the Unbalanced Magnetic Pull Mitigation by the Parallel Paths in the Stator and Rotor Windings

An eccentric rotor creates an electromagnetic force between the rotor and stator of an electrical machine. This force tends to further increase the rotor eccentricity and may severely degrade the performance of the machine, causing acoustic noise, vibration, excessive wear of bearing, rotor and stator rubbing, and so forth. Parallel connections are known to be a simple yet effective remedy for the problems associated with rotor eccentricity. We have investigated two common types of electrical machines running with eccentric rotors. We examined operation over a wide whirling frequency range. We numerically evaluated and compared the effects of parallel connections in the stator and rotor windings on the eccentricity force. We found that the parallel stator windings can be more effective in mitigating the unbalanced magnetic pull than the rotor cage (or damper winding), which normally has many more parallel circuits.     

Optimal Slot Numbers for Magnetic Noise Reduction in Variable-Speed Induction Motors

Although many empirical rules have been established for correctly choosing the number of stator and rotor slots so as to limit the audible magnetic noise level radiated by induction machines, these rules never take into account the stator natural frequencies or the fact that the motor is run at variable speed. In this paper, we present a fast simulation tool for the variable-speed magnetic noise emitted by induction machines, based on fully analytical models. On the basis of these models, we derive and experimentally validate an analytical expression for magnetic vibrations due to slotting reluctance harmonics, confirming the prime importance of slot combination in magnetic noise radiation. We ran simulations on a 700-W squirrel-cage motor in order to quantify the noise emitted by all possible combinations of slot numbers in two- and three-pole pairs, including odd slot numbers. We thus obtained a database that efficiently replaces the old empirical rules for slot combination numbers and helps in designing quiet induction motors. Similar databases can be built for other power ranges.      

三轴承支撑不平衡转子非线性动力学研究

针对具有三个滑动轴承支撑的双跨弹性转子的非线性特点,建立了数学模型,用数值积分和庞加莱映射方法对采用短同承模型的该类转子系统动力学特性随某一参数变化时稳定性的改变进行了分析,计算结果表明,系统具有发生倍周期分叉、概周期的可能,用数值方法得到系统在某些域中的分叉图,直观显示了系统在某些参数域中的运行状态和轴承几何参数变化对系统动力特性的影响,数值分析结果为该类转子－－轴承系统的设计和运动状态控制提供了理论参考。     

具有初始弯曲的不平衡转子碰摩条件的研究

建立了一个具有初始弯曲的不平衡转子模型,通过d'Alembert原理推导了振动方程。通过解析方法,分析了此类转子转静件间发生碰摩的条件。引入并求解了判断碰摩发生的碰摩因子和碰摩起始转速,分析了质量偏心量、初始弯曲长度、转子阻尼系数,和质量偏心与初始弯曲之间相位角对碰摩因子和碰摩转速的影响。该研究对于防止或预测此类转子碰摩的发生和降低碰摩带来的损失具有重要的意义。     

A General Model for Investigating the Effects of the Frequency Converter on the Magnetic Iron Losses of a Squirrel-Cage Induction Motor

We present a comprehensive analysis of iron losses in an inverter-fed induction motor. We performed experimental and numerical investigations to assess the additional losses produced by a pulsewidth modulated (PWM) supply compared to a sinusoidal supply. We developed an iron-loss model, called the hybrid model, and incorporated it into a two-dimensional (2-D) finite-element method (FEM) to investigate the losses. The model predicts the $Bhbox{-}H$ loops and the ensuing iron losses. We also used a traditional iron-loss model based on the statistical theory for the sake of comparison. We solved the nonlinear dynamic equations of the FEM by the fixed-point method and the Crank-Nicolson time-stepping scheme. We found the hybrid model to be fairly accurate in reproducing the iron losses obtained experimentally on a squirrel-cage induction motor operated under several different conditions. The numerical analysis also provided interesting results regarding the role of the PWM supply in characterizing the behavior and distribution of iron losses in the geometry of the motor.      

Effect of Magnetic Saturation on Static and Mixed Eccentricity Fault Diagnosis in Induction Motor

We have investigated the effect of magnetic saturation of core materials on the diagnosis of static and mixed-eccentricity faults in induction motors. We modeled the faults by using a modified winding function (MWF) and time-stepping finite-element (TSFE) methods to compute the stator currents of both healthy and faulty motors for processing. We then analyzed the stator signal spectra of the motors by the MWF and TSFE methods and estimated the amplitudes of sideband components attributable to the faults. The results obtained by TSFE agreed well with experimental measurements. However, there was considerable discrepancy between the MWF results and the experimental measurements. We investigated the reason for the discrepancy by analyzing the air gap magnetic field distribution in both healthy and faulty induction motors in order to determine their linear and actual magnetization characteristics. We found that, in a faulty motor, for fixed permeability, the analytic method yields a much larger magnetic flux amplitude than is actually the case. At the same time, the distribution of magnetic flux in the air gap is more asymmetric than the actual case. Here, we present our experimental results and those obtained with the MWF method, using the finite-element analysis package Opera2d 10.5, for two three-phase, four-pole, 60-Hz, 3-hp motors having 36 stator slots and 44 and 28 rotor slots, respectively.      

Effects of Armature Reaction on the Performance of a Claw Pole Motor With Soft Magnetic Composite Stator by Finite-Element Analysis

We investigated the effects of armature reaction on the performance of a three-phase three-stack claw pole motor with soft magnetic composite stator core by using three-dimensional finite-element analysis (FEA), which is an effective approach to accurately compute the parameters and performance such as the back electromotive force (EMF), core losses, and winding inductance at various saturation levels. The motor is rated as 500 W at 1800 rpm when the stator current is 4.1 A, driven by a sensorless brushless DC scheme. Because of the armature reaction, the back EMF produced by the rotor permanent magnets and the developed torque is reduced by about 3.3% at the rated load, and the core losses increase drastically by 41% from no-load to full-load. The winding inductance is computed with different loads at different rotor angles     

Development of a Spherical Induction Motor With Two Degrees of Freedom

This paper reports on the development of a spherical actuator with two actuated degrees of freedom (DOFs). The electromechanical conversion principle is that of an induction motor. The paper first discusses possibilities of adapting the actuator to a spherical rotor actuated with an unlimited angular range along two DOFs. These concepts are then characterized and compared by analytical and numerical modeling, and the final shape of the actuator, composed of a two-layer rotor with teeth surrounded by five inductors, is described. A prototype has been built, and its performance, in terms of characteristic torque-speed and efficiency, has been measured.     

Representing Elongated Magnetic Sources by Prolate Spheroidal Harmonics Developed on an Optimized Coordinate System

A method is suggested for obtaining a compact and accurate representation of elongated magnetic sources by a series expansion of prolate spheroidal harmonics. While the general solution involves an infinite series of harmonics, practical measurement grids only support discrimination of a limited number of harmonics. In this paper, we present a method for minimizing the errors introduced when terminating the series expansion. In short, the coordinate system on which the harmonics are developed, is optimized for representing the main features of the source by the first few terms of the series expansion. This allows for an early termination of the series with minimal truncation errors. The improved source representation is demonstrated for both simulated and measured sources.      

转子与定子几何不对中引起的碰摩分析

研究一类与定子几何不对中的转子的碰摩模型。通过碰摩映射的建立，将非光滑运动的研究转化为该映射的动力学研究。从几何角度分析了转子碰摩的机理，并通过数值模拟发现该类转子碰摩具有非线性系统特有的分岔和混沌等现象。     

Availability Characteristics of an Unbalanced Buffered Series Production System With Repair Priority

The steady state availability and average production rate of a single-buffer series system are obtained for a production system whose machines do not index on a common cycle and have the ability to operate at different rates. In the model which is formulated, the machines preceding the buffer are represented as a single subsystem, the input device, and the machines following the buffer are represented as a single subsystem, the output device. Simultaneous repairs are not possible and so repair priority is given to that device, input or output, with the slowest production rate. Tractable results are obtained for systems having exponential uptimes and arbitrary downtimes. These results are of use in the design of new production systems or the modification of existing ones.     

A New Sensorless Technique for the Speed Detection of an Induction Motor

1IntroductionSpeeddetechonofmotorsplaysanincreasinglyilnPortantpartinmodemmotorapplications.Amongavarietyoftechniquesareavailable,sensoriesstechniquehasbeenfollowedwithgreatinterestformanyresearherssinceitwaspresentedatthelniddleofl98o's.Inthistechl1ique,themotorisregardednotonlyasadriveInotortoprovidemechanicalenergytothelnotorsysteln,butalsoisregardedasasellsorfromwhichthespeedinformahoncanbeobtained,noadditiOna1transducerorsensorrequired.Voltage-basedlnethodalldcurrent-basedlnethodhavebee…     

非平衡磁控溅射二维磁场分布模拟计算

磁场结构在磁控溅射技术中起着重要的作用。本文利用ANSYS软件模拟计算磁场的磁感应强度及其分布,并分析、比较不同方案中的磁场分布变化规律。计算结果与实测值吻合,并且显示随着与靶面距离的增加磁感应强度减弱的特征,其中在双靶磁场并顶部磁场只有S极的结构中,磁场中磁感应强度最强。     

层状薄膜开槽波导中表面静磁波的传播特性

理论分析了传播在层状磁性薄膜开槽波导中的表面静磁波,具体计算了具有不同饱和磁化情况下,表面静磁波传播在开槽波导中的磁场分布和能量分布。     

Determining the Induction Motor Degradation State Based on Rundown Characteristics

Measurement Techniques - This paper proposes the criteria for estimating the operational condition of an induction motor, determining a degree of its degradation wear, and predicting a failure-free...     

Attenuation of Harmonic Rotor Vibration in a Cage Rotor Induction Machine by a Self-Bearing Force Actuator

In this paper, attenuation of flexural rotor vibration in electrical machines is considered. In order to generate force on the machine rotor, an electromagnetic actuator based on self-bearing machine working principle is examined. A control method for attenuating harmonic rotor vibration components is applied in a 30 kW two-pole cage induction machine. The machine is equipped with a four-pole supplementary winding for generation of lateral force on the rotor. Experimental results for the two-pole induction motor are presented. The main contribution of this paper is to apply a control method, specially designed for compensating harmonic excitations, by using a built-in electromagnetic actuator in an induction machine.      

磁悬浮转子径向位置精度的实验研究

以实际涡轮膨胀机为对象，研究了径向控制电流、工作载荷、轴承及转子的温度变化、磁场干扰等因素与转子径向位置精度的关系。提出了估计转子实际静态工作点变化的方法。实验数据表明，估计结果符合实际情况。采用该方法可监测磁悬浮轴承转子系统长期运行的安全性。