Harmonics in the Squirrel Cage Induction Motor Analytic Calculation Part III: Influence on the Torque-speed Characteristic

The harmonics that appear in the squirrel cage asynchronous machine have been discussed in great detail in the literature for a long time. However, the systematization of the phenomenon is still pending, so we made an attempt to fill this gap in the previous parts of our study by elaborating formulas for calculation of parasitic torques. It was a general demand among those who work in this field towards the author to verify his formulas with measurements. In the literature, it seems,only one detailed, purposeful series of measurements has been published so far, the purpose of which was to investigate the effect of the number of rotor slots on the torque-speed characteristic curve of the machine. The main goal of this study is to verify the correctness of the formulas by comparing them with the referred series of measurements. Relying on this, the expected synchronous parasitic torques were developed for the frequently used rotor slot numbers-as a design guide for the engineer.Thus, together with our complete table for radial magnetic pull published in our previous work, the designer has all the principles, data and formulas available for the right number of rotor slots for his given machine and for the drive system. This brings this series of papers to an end.

Harmonics in the Squirrel Cage Induction Motor,Analytic Calculation Part Ⅱ:Synchronous Parasitic Torques,Radial Magnetic Forces

The magnetic field generated in the air gap of the cage asynchronous machine and the harmonics of the magnetomotive forces creating that magnetic field,as well as the synchronous parasitic torques,radial magnetic forces have been discussed in great detail in the literature,but always separately,for a long time.However,systematization of the phenomenon still awaits.Therefore,it is worth summarizing the completeness of the phenomena in a single study–with a new approach at the same time-in order to reveal the relationships between them.The role of rotor slot number is emphasized much more than before.New formulas derived for both synchronous torques and radial magnetic forces are used for further investigation.It will be shown that both phenomena in subject must be treated together.Formulas will be provided to take into account attenuation.Design guide will be provided to avoid dangerous rotor slot numbers.It will be shown that the generation of synchronous torques and radial magnetic forces do not depend–in this new approach-on the slot combination,but on the rotor slot number itself.

Harmonics in the Squirrel Cage Induction Motor Analytic Calculation-Part Ⅰ: Differential Leakage, Attenuation, Asynchronous Parasitic Torques

The magnetic field generated in the air gap of the cage asynchronous machine and the harmonics of the magnetomotive forces creating that magnetic field, as well as the related differential leakage, attenuation, asynchronous parasitic torques have been discussed in great detail in the literature, but always separately, for a long time. However, systematization of the phenomenon still awaits. Therefore, it is worth summarizing the completeness of the phenomena in a single study – with a new approach at the same time-in order to reveal the relationships between them. The role of rotor slot number is emphasized much more than before. An existing, commonly used, but still impractical basic figure has been modified to more clearly demonstrate the response of the rotor for the harmonics of the stator. The need to treat differential leakage, asynchronous parasitic torques and attenuation together will be demonstrated: new formula for asynchronous parasitic torque is derived;the long-used characteristic curves for differential leakage and attenuation used separately so far was merged into one, correct curve in order to provide a correct design guide for the engineers.

Intelligence Based Soft Starting Scheme for the Three Phase Squirrel Cage Induction Motor with Extinction Angle AC Voltage Controller

Whenever a squirrel cage induction motor is started, notable electromechanical torque and current pulsations occur. The adverse effects of starting torque pulsations and high inrush current in induction motor are eliminated using digital power electronic soft starting schemes that guarantee higher degrees of compliance of the requirements of an ideal soft starter for the induction motor. Soft starters are cheap, simple, reliable and occupy less volume. In this paper, an experimental setup of soft starting technique with extinction angle AC voltage controller and a speed and stator current based closed loop scheme is demonstrated using Artificial Neural Network (ANN) and Fuzzy Logic Control (FLC) by the way of MATLAB/SIMULINK based simulation. The ANN based soft starting scheme produces best results in terms of smooth starting torque and least inrush current. The results thus obtained were satisfactory and promising.

CALCULATION OF SATURABLE LEAKAGE REACTANCES OF SQUIRREL CAGE ASYNCHRONOUS MOTORS

A general method of calculating the saturable leakage reactances of squirrelcage asynchronous motors is presented.The method synthesized the variety of effectswhich affect the saturation of leakage magnetic circuit.And the saturable reactances canbe precisely evaluated in any running condition.The computation results of Y-series mo-tors are in good agreement with the test ones.

Time-stepping finite element analysis on the influence of skewed rotors and different skew angles on the losses of squirrel cage asynchronous motors

To study the influence of skewed rotors and different skew angles on the losses of squirrel cage asynchronous motors,a 5.5-kW motor was taken as an example and the multi-sliced field-circuit coupled time stepping finite element method(T-S FEM)was used to analyze the axially non-uniform fundamental and harmonic field distribution characteristics at typical locations in the stator and rotor cores.The major conclusions are:firstly the skewed rotor exhibits a decrease in the harmonic copper losses caused by slot harmonic currents in the stator winding and rotor bars.Secondly,the skewed rotor shifts the non-uniform distribution of field in the axial direction,which leads to more severe saturation and an increase in iron losses.The heavier the load,the more pronounced the increase in iron losses.Furthermore,the influences of different skew angles on motor losses are studied systematically,with skew angles from 0.5 to 1.5 stator tooth pitch.It is found that the lowest total loss occurs at 0.8 stator tooth pitch,and the slot harmonics can be decreased effectively.

三相鼠笼异步电动机无传感器转速检测技术及其适应性

针对三相鼠笼异步电机无位置传感器快速傅立叶变换(fast Fourier transformation,FFT)测速方法需要预先知道转子槽数,且测试精度易受噪声干扰和采集时长等因素的影响,提出一种基于奇异值分解-Prony(singular value decomposition-Prony,SVD-Prony)算法的无位置传感器高精度转速测量技术。运用电机学相关理论,研究转子槽谐波测速机理,并给出整数倍率转子槽数的计算方法。在分析并明确定子电流噪声影响和FFT法存在检测精度受采样时长限制等问题的基础上,研究基于奇异值增长率的SVD滤波方法和用于辨识转子槽谐波的Prony算法,并以Y160M-4型电机为研究对象,在不同运行状态下对该技术的适应性进行分析。在此基础上,构建相关物理测试平台,对YE90S-2型电机进行实测。结果表明,在相同采集情况下,所提方法测试绝对误差仅为FFT测速方法的几分之一,检测精度大幅提高。

鼠笼式电机转子钎焊模卡导条拉脱原因分析及解决措施

某型机车牵引电机鼠笼式转子端环与导条模卡钎焊外观检查合格后进行拉伸试验,部分端环-导条钎焊接头的导条从焊缝位置拉脱,不能满足抗拉强度要求。为解决该问题,通过渗透探伤和宏观检测发现端环内侧与导条的钎缝界面存在微裂纹、钎料填充不致密和分层等缺欠。端环-导条结构设计不合理以及钎焊高温持续时间不足是导致拉脱问题的主要因素。针对这两个因素提出了改进方案:端环槽深由6 mm改为4 mm、增加端环槽内侧45°倒角,冬季钎焊时450℃保温时间延长为90 s。改进后经拉伸试验验证,成功解决了导条拉脱的问题,保障了产品质量。

鼠笼转子端部扭振特性研究及其对结构可靠性影响

针对变频器驱动下牵引电机受到谐波转矩的影响,分析了谐波转矩对铜条式鼠笼转子结构的作用机理。采用试验与仿真相结合的方法识别鼠笼转子端部特性。首先,通过模态分析,获取了鼠笼转子的模态参数;然后,建立了基于模态试验的转子等效有限元模型,分析了其在12倍频特征电磁激励下的静强度及谐响应。最后,基于导条振动测试平台,研究了鼠笼转子端部扭振特性,并对载荷放大效应进行了验证,为提升铜条式鼠笼转子端部结构的可靠性提供了一定的理论支撑。

机车牵引电机转子模态试验及仿真优化研究

牵引电机转子作为电机旋转的核心,转子的固有频率应避开实际的工作频率、工作转速。基于软件的有限元分析法是目前在设计阶段应用最广泛的固有频率计算方法,而影响计算结果准确性包括材料参数、各部件间的实际接触状态等。通过LMS公司的采集系统进行实际模态测试,并采用Ansys的有限元分析法,考虑导条和端环、导条和铁心、铁心和转轴实际接触状态计算转子的固有频率。根据实际模态测试结果,以验证Ansys计算结果的实效性,为进一步提高牵引电机转子模态仿真精度提供有益参考,也为进一步改进转子结构,保证转子在实际运行中不会发生共振提供依据。

鼠笼弹性支承刚度的数值仿真及影响因素研究

为了能准确获得鼠笼弹性支承的刚度特性,对鼠笼刚度进行了理论分析、数值仿真和试验测试研究。首先,对鼠笼进行了网格无关性检验,研究表明,鼠笼条网格和鼠笼条根部圆倒角网格对鼠笼刚度计算结果影响明显。其次,研究了外力加载方式对鼠笼刚度的影响,研究表明,在不考虑轴承建模时,不同的外力加载方式会使得鼠笼承力端产生不同程度的形变而影响鼠笼的刚度;考虑轴承建模时,外力加载方式对鼠笼刚度的影响减小,且数值仿真结果趋近于通过刚性域加载得到的鼠笼刚度。最后,设计并搭建了鼠笼刚度试验测试平台,得到了鼠笼刚度的试验值,验证了数值仿真的正确性及合理性。

6kV浆液循环泵电机定子绕组接地故障分析及预控

某600 MW火电机组6 kV脱硫浆液循环泵电机在机组降负荷后短时升负荷时,带载热态启动过程中出现速断保护动作现象,测量电机绝缘电阻为零,更换备用电机运行。通过对电机解体,发现转子鼠笼端环焊块脱落、定子绕组外绝缘破损严重,确定绕组接地造成保护跳闸,从保护定值、运行操作、规程要求、检修维护多方面分析根本原因,提出工作票及运行规程优化建议,为预控此类故障提供参考思路。

工况对鼠笼式电装的影响性分析

核电用某型闸阀在进行无介质、有介质、蒸汽介质3种不同工况下的动作性能检查时,在无介质、蒸汽介质工况下执行开启动作至开阀灯亮后阀门出现明显撞击声,执行关闭动作瞬时断电后阀门自由下行至关阀灯亮等异常现象。经过数据分析后得出阀门采用的鼠笼式电装在无介质、蒸汽介质工况下运行惯量、断电后转动力矩过大,导致位置信号失去作用,引发阀门出现过开、过关等异常现象,严重损伤了阀门机械部分零件的使用寿命。经过调整阀门用鼠笼式电装后在无介质、有介质、蒸汽介质3种不同工况下进行动作性能试验,均未出现阀门过开、过关等异常现象。本文对鼠笼式电装存在的表观现象进行汇总、分析。

基于永磁辅助转子和改进磁障的笼型感应电机的研究

为了有效提高笼型感应电机的功率因数,通过对传统三相四极笼型感应电机的转子结构进行改造,提出了一种基于永磁辅助转子和改进磁障的新型笼型感应电机。采用二维瞬态有限元分析方法,对比和分析了所提新型感应电机和传统感应电机在磁路分布、磁通密度、功率因数和效率方面的性能差异。结果表明,相比于传统感应电机,所提出的新型感应电机可将功率因数提升至0.86~0.98,效率最高可达到95.5%,新型感应电机能够在优化的功率因数下更加高效地运行。

鼠笼异步电机多故障智能诊断基本研究

围绕鼠笼式异步电动机的结构、工作原理及其多故障智能诊断技术进行了深入研究。介绍了鼠笼电机的构造和基本工作原理,包括其定子和转子的主要组成部分,以及电机的起动和运行机制。分析了鼠笼电机可能出现的机械和电气性质故障,如转子断条和轴承故障,并推导了相应的故障特征频率分量,阐述了其在故障诊断中的作用。指出了鼠笼电机故障诊断的难点和现有技术的局限性,并提出了基于参数测定和机器学习技术的智能诊断方法。强调了智能故障诊断技术在保障工业生产连续性和安全性方面的重要性,并展望了未来的研究方向和技术发展。

异步电动机的转子断条问题研究

讨论了异步电动机转子断条故障的特征机理,介绍了通过定子电流监测进行故障诊断的方法。概述了鼠笼式异步电动机转子断条故障可能由机械应力、过载电流和设计缺陷等因素引起,并强调了这种故障对电机性能的负面影响,包括转速异常、噪声增大和潜在的安全风险。提出了通过监测气隙磁场变化和定子电流频谱分析来诊断故障的方法。在正常情况下,电机磁动势平衡对称,而转子断条破坏了这种对称性,导致转矩波动和平均转矩下降。通过对定子电流进行频谱分析,检测到特定的谐波分量。提出结论,尽管传统理论侧重于基波的影响,实际上其他定子电流成分也参与了谐波的生成,并且可以通过监测特定频率的谐波分量来判断转子是否存在断条故障。

STATCOM/VRB改善笼型风电机组性能的控制策略

为了提供笼型机组发电时所需无功功率并平滑笼型机组有功功率的波动,将无功功率补偿装置STATCOM与VRB储能系统合二为一构成STATCOM/VRB装置,用以改善笼型风电机组性能。首先构建了STATCOM/VRB数学模型;然后研究系统各部分的控制策略,通过在STATCOM/VRB装置的DC/DC变换器处加装模糊控制器,并提出一种基于模糊自适应的STATCOM/VRB控制策略;最后在MATLAB/Simulink环境下进行仿真研究,结果表明在风速骤升和骤降两种情况下该控制策略依然可以有效平抑风电功率波动并维持储能系统工作在合理状态,有效提升电网安全运行水平。

Dynamic stiffness characteristics of aero-engine elastic support structure and its effects on rotor systems:mechanism and numerical and experimental studies

The support structure of a rotor system is subject to vibration excitation,which results in the stiffness of the support structure varying with the excitation frequency(i.e.,the dynamic stiffness).However,the dynamic stiffness and its effect mechanism have been rarely incorporated in open studies of the rotor system.Therefore,this study theoretically reveals the effect mechanism of dynamic stiffness on the rotor system.Then,the numerical study and experimental verification are conducted on the dynamic stiffness characteristics of a squirrel cage,which is a common support structure for aero-engine.Moreover,the static stiffness experiment is also performed for comparison.Finally,a rotor system model considering the dynamic stiffness of the support structure is presented.The presented rotor model is used to validate the results of the theoretical analysis.The results illustrate that the dynamic stiffness reduces the critical speed of the rotor system and may lead to a new resonance.

免耕播种机鼠笼型地轮参数优化

地轮是免耕播种机的主要工作部件,可为播种机提供播种和施肥动力,地轮的结构与参数影响着播种机的作业质量。为降低滑移率,减少漏播、空穴和施肥量不足等问题,以鼠笼型地轮为研究对象,通过选取地轮直径、地轮轮宽与垂直载荷为试验因素,采用单因素及三因素三水平正交试验设计方法,进行单间试验及方差分析。研究结果表明:影响滑移率和地轮摩擦力主次因素为垂直载荷>地轮直径>地轮轮宽;确定最佳因素组合为垂直载荷350N、地轮直径610mm、地轮轮宽126mm。此时,地轮滑移率值为1.93%,地轮摩擦力值为330N。

鼠笼弹性支承干摩擦减振试验研究和参数识别

针对鼠笼弹性支承干摩擦阻尼器减振机理和摩擦参数不确定问题,提出了基于双线性梁单元简化模型的两步参数识别方法。基于梁单元弯曲理论和有限元分析,开展刚度分析并提出鼠笼弯曲刚度经验计算公式,相比传统理论公式误差更小,为参数识别提供初值条件。建立了鼠笼弹性支承干摩擦试验台,改变鼠笼端面接触压力,开展了鼠笼弹性支承扫频试验,得到了表征界面能量耗散特性的黏滞-滑移特性曲线和最佳正压力。基于鼠笼弹性支承黏滞-滑移曲线,采用遗传算法开展了梁单元与双线性弹簧单元两步参数识别,开展了参数识别结果验证和误差分析。试验结果表明,双线性梁单元简化模型迟滞曲线面积误差在10%以内,相比三维有限元模型,计算时间缩短了92.34%。该模型可为鼠笼弹性支承干摩擦减振设计提供一种高效的简化计算模型。