Selection criteria of induction machines for speed-sensorless drive applications

Induction motors, both three and single phase, are used extensively for adjustable-speed drives' applications. These machines are structurally very robust and are a primary source of motive power and speed control where DC machines cannot be used. For closed-loop control of these machines, sensorless speed estimation is usually preferred. Among the current estimation techniques available for speed-sensorless induction motor drives, speed measurement based on rotor-slot-related harmonic detection in machine line current happens to be a prominent one. While these harmonics can be strong in certain kinds of machines, some other machines may exhibit very weak rotor slot harmonics that can be obscured by noise. Skewing, slot shapes and types, structural unbalances, etc., also have a prominent effect on the detectability of these harmonics. This paper attempts to investigate this problem based on the interaction of pole pairs, number of rotor bars, and stator winding. Although the analysis and experimental results have been mainly provided for three-phase squirrel-cage induction motors, single-phase and slip-ring induction motors have also been addressed. Further, it has been shown that eccentricity-related fault detection could also be easily accommodated with this kind of speed detection technique at no or negligible extra cost when certain motors are selected.     

大线规发卡式漆包膜包线圈成型技术

发卡电机因槽满率高、散热好、体积小、性价比高等优势而广泛应用于新能源汽车领域,但发卡式线圈通常是小线规。与小线规电机相比,大线规电机功率更大。详细阐述了大线规发卡式漆包膜包线圈的结构及成型难点,以及针对冲压成型和挤压成型2种工艺方法在U形成型和端部成型试验验证过程中出现的问题进行了影响分析,并针对出现的导线破损等质量问题在工艺方法、模具、操作等方面进行了改善,最终得到了较满意的线圈成型效果。     

耐电晕特种绕组线的制造及应用

本文主要介绍了两种耐电晕性好,绝缘厚度薄,机电性能优良,而且导热、耐热性都很高的新型绕组线。一种是耐电晕薄膜绕组线,另一种是耐电晕特种漆包绕组成,可适用于牵引电机、变频电机以及高压电机等。     

双定子永磁电机内外定子绕组相轴相对位置确定方法

确定内外定子绕组相轴相对位置是双定子永磁电机设计安装过程中必须解决的问题.本文推导了永磁电机定子绕组相轴位置与电机设计参数关系的解析表达式,并分别以整数槽、分数槽绕组电机为例,将解析表达式求解结果与槽导体电势星形图分析结果进行对比;采用有限元方法分别计算了内外定子均为分数槽和内定子为整数槽外定子为分数槽两种情况下的双定子永磁电机电磁特性;最后测试了内外定子均为分数槽样机绕组的相电动势波形.研究结果表明:解析表达式分析结果与槽导体电势星形图分析结果完全一致,有限元分析结果与实验结果吻合很好,验证了理论分析的正确性.本文所得解析表达式能准确计算永磁电机定子绕组相轴位置,适用于三相60°相带分数槽双层分布式、集中式绕组电机及整数槽绕组电机.     

Improving motor efficiency levels globally

Today's premium efficiency motors motors for the North American market are the result of focused efforts over the last decade. The advantages of using premium efficiency motors have been discussed and well documented. The U.S. Energy Policy Act (EPAct) of 1992 legislation and the Canadian Energy Efficiency Act, along with the implementation of NEMA Premium efficiency levels, have led to North American leadership on motor energy conservation. The technical evaluation of extending these premium efficiencies to the International Electrotechnical Commission (IEC) 50-Hz motors is provided along with an analysis of energy savings if these motors were available and used. Many variables are considered when energyefficient motors are designed for the world market. The following factors should be considered: 1) motor performance requirements [e.g., torque and lockedrotor amps (LRAs)] 2) frequency 3) voltage 4) test methods for efficiency 5) allowed tolerances 6) application requirements 7) target efficiencies 8) energy costs. All these factors must be taken into account and evaluated individually to determine if it is possible to achieve the NEMA premium level of efficiency. Standardization would yield considerable benefits if the 50- Hz design is just a minor modification or rerate (as defined in the "Performance Differences Between 50- and 60-Hz Machines" section) of the 60-Hz design or vice versa. This article will review the different efficiency test methods seen in the IEEE and the IEC Standards, the different performance requirements, and how these may affect the design and possibly the efficiency. It will also show why 50-Hz machines tend to have lower efficiencies than 60-Hz machines. The current status of international efficiency standards as of May 2007 is reviewed, and then motor population data from a large chemical facility are used with these standards to quantify the potential savings available if premium efficiency motors were available worldwide.     

定子双绕组电机槽漏感计算与绕组分布关系的研究

对于定子双绕组电机,两套定子绕组共存于同一槽中,存在互漏感磁链耦合,槽漏感的计算与绕组节距、两套绕组夹角及绕组在槽中的分布有一定的关系,其计算不能套用现有的计算公式,需要进一步地研究。本文主要采用解析法研究不同绕组分布形式下的定子双绕组电机槽漏感的计算问题,导出了相同匝数两套绕组槽自漏感、互漏感与节距之间的关系式。     

Increased Efficiency Versus Increased Reliability

The vast majority of totally enclosed fan cooled (TEFC) squirrel cage induction motors in the 1-to 20-hp range installed in the petroleum and chemical industries are National Electrical Manufacturers Association (NEMA) "T" frames built prior to 1992, NEMA "T" frames built in accordance with the Energy Policy Act of 1992 (commonly referred to as EPAct motors), and the NEMA Premium motors, introduced after the year 2000, that exceed the EPAct efficiency standards. All three types are available in accordance with the IEEE 841 recommended practice and standards. The most obvious difference in these three generations of motors is their efficiency levels. There has been some concern expressed by the users of these motors that to achieve the premium levels of efficiency it was necessary to compromise other performance characteristics and the motor reliability. This article addresses these claims and shows that they are without basis.     

Effect of surge voltage risetime on the insulation of low-voltagemachines fed by PWM converters

This paper investigates the repetitive surge-voltage withstand of low-voltage mush-wound machines operated on adjustable-speed drives (ASDs) using insulated gate bipolar transistor (IGBT) semiconductor technology. Historical work on surge testing of motor insulation has focused on one or more of the following aspects: (1) large horsepower motors; (2) medium-voltage form-wound motors; (3) single-shot impulse-type transients; or (4) low-voltage machines with surge risetimes >200 ns. IGBT drives can have risetimes of 50-200 ns. Thus, a new study on electrical stress of insulation systems due to the nonlinear voltage distribution of mush-wound motors when subjected to repetitive steep dV/dt square-pulse waveforms (rather than impulse wave testing) is presented. Magnitude and risetime of the repetitive ASD surge-voltage transient induced on the machine terminals is reviewed first. Next, surge propagation into the winding was investigated to identify maximum voltage stress points on the conductor insulation. Potential failure mechanisms observed at these points are then discussed. The significance of decreasing surge risetime and increasing cable lengths on internal nonlinear voltage distribution is studied with experimental results from a 7.5-hp motor with a tapped stator winding     

Analysis of armature reaction and winding inductances of permanent magnet brushless DC motor with deep slot concentrated coils

Based on the configuration of deep slot concentrated coils, an analytical model is developed for predicting the armature reaction field produced by the 3-phase stator windings of permanent magnet brushless DC motors with concentrated coils by using the image method and the analytical functions of the armature reaction and winding inductances are proposed accounting for the influence of stator slotting. This approach is different from the method of equivalent distributed current sheet and more suitable for electric machines, which have concentrated coils and deeper slots. Under different control mode, the different analytical functions are presented. This will be helpful when further analyzing the performance of the motor. The results agree with the experiment very well. __________ Translated from Proceedings of the Chinese Society for Electrical Engineering, 2005, 25(12): 127–132 (in Chinese)     

特殊电机用漆包线的发展

本文以 8 0～ 90年代部分特殊电机用漆包线的国内外发展情况回顾我国绕组线的发展概况 ,并展望今后的发展动向和市场前景。指出 ,目前我国已经是世界上绕组线的生产大国 ,但要真正成为一个高技术的绕组线生产大国 ,还必须脚踏实地的努力于基础工作     

不等齿顶宽间隔绕组对直接驱动转台电机转矩特性的影响

为了满足直接驱动数控转台对低速大转矩电机的要求,研究并设计了一种基于极槽数相近结构的不等齿顶宽间隔绕组多极永磁同步电机。多极电机保证了转台具有较低的额定转速。极槽数相近结构不仅可以提高绕组短距系数,更能有效地降低电机的齿槽转矩波动。间隔绕组和不等齿顶宽结构的配合设计最大化了定子齿磁链和绕组系数,从而有效地提高了电机的转矩密度。另外,还采用解析计算方法分析了不等齿顶宽结构对齿槽转矩波动和谐波绕组系数的影响。从有限元软件ANSYS计算结果和实验结果可以看出,样机的齿槽转矩波动小于额定转矩的1%;与等齿宽电机相比,不等齿顶宽结构有效地提高了电机的平均转矩,证明了所提出设计方法的正确性和有效性。     

YKS710-2A型异步电动机的改造

广东粤阳发电有限公司YKS710-2A型6kV给水泵异步电动机自投入运行以来,电动机线圈的温度一直偏高,并出现磁性槽楔脱落的现象。在对线圈温度升高的原因进行分析的基础上,提出了降低绕组热负荷和加强散热的电动机改造方案。通过减少绕制线圈时并绕导线的数目,使导线截面积增大,减小热负荷;在定子铁心项部增加挡板,提高了绕组的冷却效果;此外,采用模压工艺绕制线圈以提高主绝缘的可靠性,以普通槽楔代替磁性槽楔,避免槽楔脱落。改造后的线圈样品试验和运行情况表明,线圈的耐冲击水平较高,运行温度明显降低。     

变频牵引电机定子绕组绝缘老化特性研究

对比测量了不同运行年限的变频牵引电机的定子绕组绝缘诊断参数,包括绝缘电阻、介质损耗因数、局部放电起始电压(PDIV)、剩余击穿电压等特征参数,以及沿绕组不同部位的绝缘材料取样进行了热失重分析(TGA)来研究绝缘老化特征。介电性能测量结果表明,与新电机相比,运行后定子绕组的绝缘介电性能有不同程度的下降,出槽口附近绝缘的老化程度高于槽内。TGA分析结果表明,使用了长达10年的牵引电机定子绕组绝缘性能略有下降,且线圈下层边的绝缘老化比上层边明显。     

转子甲类波绕组排列方法的探讨

为方便绕线型异步电动机的设计和接线操作,明确转子波绕组一端接线法十分必要。从电角度的观点出发确定三相绕组首端引出线位置。根据波绕组的连接规律进行各相带的槽号分配,进而利用Excel公式法编排绕组表。这种方法不但易于掌握,而且通过绕组表可直观的确定上下层整距、短距、引线线圈所在槽号,为绘制转子接线图和设计转子线圈奠定了基础。     

电动嵌线器的设计原理与应用

设计了一种微型电动嵌线机,该电动嵌线器用一微型直流电动机作动力,可直接将漆包线绕到吊扇电动机定子槽中,省去了手工下线时的许多步骤。且绕线紧凑,比手工下线节省漆包线。     

Understanding surface partial discharges in HV coils and the role of semi-conductive protection

An electrical insulating system in high voltage rotating machines is subjected to several stresses that cause changes of material properties during its lifetime. This phenomenon reduces progressively ability of the insulation to withstand the service stresses. Internal partial discharges can be located inside the high voltage insulation and usually they are dangerous for life-cycle duration. Surface discharges are generated at the solid/air interface in the gaps of machine stator slots or at the slot exits. Surface discharges can cause more intensive deterioration of the insulation, accelerate aging processes and definitively take aim toward premature failure of the machine. The application of conductive or semi-conductive protection layer provides certain protection for solid insulation from these discharges. Semi-conductive corona protection tapes are used on the coils at the slot exit region to electrical field control and prevent surface discharges. Laboratory measurements of the surface partial discharge quantities in specimens of high voltage coils with mica insulation were performed. The aim of the paper is to describe theoretically the development of surface discharges in rotating machines and to present surface partial discharge development in HV motors when semi-conductive layer protection is missing. The results can be found useful to understand better the surface discharge development and importance of high-quality semi-conductive protection technology.     

Memory motors

A new class of permanent-magnet (PM) machines, named memory motors for their ability to change the intensity of magnetization and memorize the flux density level in rotor magnets is described in the article. A memory motor can be built either as a variable-flux or pole-changing machine. In both machine types, the magnetization of PMs can be simply varied by a short current pulse, with no need for permanent demagnetizing current as in conventional internal PM machines at flux-weakening mode. The demagnetizing current flows through stator winding(s) supplied from the same source as the stator current. Memory motors combine advantages of a wound-rotor machine (variable rotor flux) with those of a wide-speed machine (no excitation losses), resulting in a unique machine concept that has the potential to find numerous applications in electric drives.     

电机在制造过程中降低温升的对策

论述了电机制造阶段为降低运转时绕组的温升应密切关注绕组浸漆质量、电机散热的各大小环节,杜绝增加各种损耗的劣质冲片、铝水杂质、细条、断条等因素,电机制成后降低绕组温升的办法可车小转子外圆和换成磁性槽楔或磁性槽泥。这些都是降低温升,提高电动机品质的内在潜力。     

高压电机定子采用散绕组的绝缘结构分析

高压电机的定子通常采用成型绕组,同时需配套开口槽,导致电机成本增加、气隙磁场谐波含量增大、齿槽转矩增大等一系列问题。为了解决上述问题,可以采用散嵌圆铜线绕组。对于高压电机采用散绕组,绝缘问题是关注和研究的重点。以1台高压散绕组电机为例,利用有限元法分析了高压电机采用散绕组的绝缘结构可靠性,分别分析了匝间绝缘、主绝缘、层间绝缘和端部绝缘的绝缘情况以及主绝缘被冲片毛刺划伤情况下的电场强度分布,并根据分析结果针对电机槽内绝缘做出了优化,制造了1台样机并对样机进行了耐电压试验。验证了高压电机定子采用散绕组在一定程度上是可行的,为高压电机定子绝缘结构设计提供了参考。     

单绕组多速电动机的设计和探讨

单绕组双速异步电动机是变极电机中方法最简易、应用最广泛的一种变极调速方法。变极电机的设计中,花费时间最多的是研究绕组的排列。通过槽电流表和槽磁动势图定性地分析电机的谐波磁场对电机运行性能的影响,由此确定电机所选槽配合是否合适。在工厂中,通过对现有的单速电机进行绕组改绕来设计单绕组多速电机。改绕计算主要是计算电动机磁路各部分磁通密度数值,不使其过大而致铁心严重饱和。在设计与计算过程中需要综合考虑2种极数下电机性能的特点。