Stray load loss analysis of induction motor-comparison of measurement due to IEEE standard 112 and direct calculation by finite-element method

The purpose of this paper is to specify the main components of the stray load loss of induction motors from both results of measurement and analysis. The IEEE standard 112 Method B is applied to the cage induction motor for the measurement of the stray load loss. On the other hand, the losses generated at the stator core, the rotor core, and the rotor cage are calculated directly by the finite-element method considering the magnetic saturation and the harmonic fields, which vary due to the load condition. The measured and the calculated torque, losses, and efficiency agree well. It is clarified that the main parts of the stray load loss in the case of the analyzed motor are the increase of harmonic losses due to load, which are the harmonic Joule losses of the rotor cage and the harmonic core losses of the stator and the rotor. The relationships between the losses separated by the measurement and the losses calculated directly by the finite-element method are also clarified.     

Thermal effects of stray load losses in induction machines

Additional heat produced in induction machines due to stray load losses could influence the plant rating, winding insulation design, operating limit and the machine protection design. Quantifying this additional heat and stray load losses accurately and, hence, investigating the extent of some of these influences are the concerns of this paper. Two experimentally verified models, electrical and thermal, are presented. Results of a practical exercise on the measurement of stray load losses by different test methods are reported. The study, thereafter, gives insight into the relationship between stray load losses and the influences mentioned above and contribute results, which are useful to the design and operation of this machine and its protection     

When loads stray: Evaluation of Different Measurement Methods to Determine Stray Load Losses in Induction Machines

The efficiency data provided by manufacturers are measured or calculated according to different national and international standards. These standards use different means to incorporate the stray load losses; thus the efficiency values obtained from different testing standards can differ by several percent. This leads to problems in competition and to a potentially confusing situation for the manufacturers and customers. This paper evaluates different measurement methods to determine stray load losses in induction machines.     

异步电机高频杂耗的自适应时步法有限元计算

异步电机杂散损耗的准确计算是一个十分困难的问题。本文论述了对非斜槽异步电机高次谐波杂散损耗的计算方法。文中采用的数学模型把电磁场有限元方程与电路方程耦合在一起,当输入电压波形给定后,电机中的之流和磁密波形可通过时步法直接求得。根据计算所得的高次谐波电磁场,就可进一步计算出高次谐波杂散损耗。计算结果通过样机试验得到验证。在计算中采用了自适应时间步长的方法,并首次提出了一种估计局部截断误差简单实用的方法。     

异步电动机轻载调压节能技术研究

从电动机的损耗分析出发 ,详细研究了异步电动机轻载调压节能的原理、途径和负载系数的测定方法 ,并介绍了一种用单片机实现的三相异步电动机轻载调压节能和综合保护控制器 ,对电动机节能技术的推广应用有一定的指导意义。     

电动机损耗的比例变化规律及其对策

三相交流电动机的损耗可分为铜耗、铝耗、铁耗和杂散耗、风摩耗,前4种为发热损耗,其总和称为发热总损耗。阐述当功率从小到大变化时,铜耗、铝耗、铁耗、杂散耗对发热总损耗的比例变化。通过实例,铜耗和铝耗占发热总损耗的比例虽有波动,总体上由大变小,呈下降趋势。而铁耗杂散耗相反,虽有波动,总体上由小变大,呈上升趋势。功率足够大时,铁耗杂散耗超过了铜耗。有时杂散耗还超过了铜耗、铁耗,成为发热损耗的第一因素。再分析Y2电动机,以及观察各种损耗对总损耗的比例变化,揭示的规律类似。认识上述规律,得出不同功率电机降低温升和发热损耗的侧重点不同。对小电机,首先应降低铜耗;对中大功率电动机,应侧重降低铁耗杂散耗。认为"杂散耗比铜耗、铁耗要小得多"的观点是片面的。特别强调,电动机功率越大越要注意降低杂散损耗。中大容量电动机采用正弦绕组来降低谐波磁势及杂散耗,效果往往很好。而降低杂散损耗的各种措施,一般不需要增加有效材料。     

基于二维解析法的光滑表面实心转子感应电机附加损耗的研究

在普通异步电机中，由于附加损耗数值较小，通常按总功率的5%粗略估算。在实心转子感应电机中，附加损耗中的表面涡流损耗数值远大于普通笼型感应电机，不但成为实心转子感应电机附加损耗的主要部分，而且是造成这种电机效率低、电机过热的重要原因，限制了该类电机的应用和发展。文中运用二维解析法及坡印亭定理对实心转子的表面涡流损耗进行了计算，与试验结果比较显示，理论计算在小转差范围(0~0.2)内取得了与实际较为一致的结果，并分析了大转差下产生偏差的原因。在小转差(s=0.107)运行状态，对定子槽口宽度变化和气隙长度变化对转子表面涡流损耗影响进行仿真计算。结果表明，改变槽口宽度对该种电机转子的表面涡流损耗影响不明显，随着气隙长度的增加，附加损耗曲线分为快速下降，缓慢下降两段。在曲线缓慢下降段综合考虑选取气隙长度是合适的。     

Stray losses due to inter-bar currents of skewed cage induction motors at no-load

Contents In accordance with present-day efforts to reduce power losses in electrical machines, an analytical approach to estimate the influence of contact resistances between the skewed rotor cage and its laminated iron core on the amount of stray losses of induction motors is made in this paper. Equations for calculation of resistances of the rotor iron core, with which the stray losses due to inter-bar currents are taken into account, are presented.

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übersicht In übereinstimmung mit neuzeitlichen Bemühungen, die Verluste von elektrischen Maschinen zu vermindern, ist in der vorliegenden Arbeit eine analytische L?sung zur Bewertung des Einflusses der Kontaktwiderst?nde zwischen dem geschr?gten K?fig und Blechpaket des Rotors auf die Zusatz und indirekt auf die Gesamtverluste von Asynchronmaschinen angegeben. Es werden die Gleichungen zur Berechnung des Blechpaket-Widerstandes des Rotors angegeben, mit denen man den Anteil der Zusatzverluste berechnet die, der von Querstr?men im Rotor verursacht wird.

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Received: 21 March 2000     

Assessing the impacts of rewind and repeated rewinds on induction motors: is an opportunity for Re-designing the machine being wasted?

This paper describes an extensive induction motor rewind study. The consequent effects during the rewind process on loss components and efficiency are investigated. All the tests are conducted in accordance with the IEEE 112-B method, and some results are justified by the calorimetric approach. The conclusions drawn from the study show a little impact of rewinding or repeated rewinding on the motor losses and efficiency if "good practice" is followed strictly. The efficiency results presented for most rewind studies apply for the full load condition. Changes in the balance between the load-independent losses and the load losses resulting from rewinding can, however, cause the maximum efficiency point to occur at a load, which differs from that of the original design. This may or may not be a disadvantage. Since few motors actually operate continuously at a full load, the comparisons of efficiency should really be made at the load point that applies specifically to the individual motor being rewound. The question that then arises is whether, there is a chance of improving the energy efficiency by modifying the motor design during rewinding, so that, a maximum efficiency occurs at the actual load point of the motor when used for its particular application.     

Symmetrization of an Induction Capacitor Motor by Methods of Mathematical Modeling

Reducing electrical losses and increasing energy performance are priorities when designing electrical machines. In addition, increasing initial costs related to electric machine manufacturing owing to an increase in the consumption of active materials are relatively quickly compensated by decreasing operating costs. For single-phase motors, in particular, the capacitor induction motors with electric and magnetic asymmetry, improving ways of reduce electric losses is a very important problem, to solve which it is necessary to study processes of their symmetrization. The design procedure of working and energy characteristics of induction capacitor motors based on the results of solution of electromagnetic equations is proposed. The parameters of phase-shifting capacitor and the motor transformation ratio are determined at which there is a circular magnetic field within the air gap. It is shown that the calculation results can be used for building the graph dependences of transformation coefficient, capacitor capacitance, and capacitor voltage on slip and subsequent analysis of these curves to obtain the most appropriate solutions.     

非晶合金永磁电机负载损耗及效率特性分析

为了研究采用非晶合金材料代替硅钢片材料制作铁心后,永磁电机在负载运行时的损耗与效率的变化规律,研制了两台相同结构尺寸参数的非晶合金永磁电机和硅钢片永磁电机。利用实验方法测试了两台电机在相同运行工况下的损耗与效率特性,并借助有限元方法对两台电机不同负载率时的损耗进行了对比分析。结果显示,轻载时,非晶合金永磁电机定子铁心损耗低于硅钢片电机,效率优势明显;但随着负载率的增加,非晶合金电机定子铁心饱和严重,导致绕组磁动势波形畸变,由绕组磁动势谐波引起的损耗高于硅钢片电机,非晶合金电机效率优势随负载率的增加逐渐减小。     

Modeling of iron losses of permanent-magnet synchronous motors

Permanent-magnet (PM) motors offer potential energy savings as compared with induction motors because of the virtual elimination of rotor loss and the reduction of stator loss from operation near unity power factor. In PM machines, iron losses form a significant fraction of the total loss partly due to the nonsinusoidal flux density distribution. Design optimization therefore requires good means of predicting these iron losses. Finite-element analysis can be employed but this approach is cumbersome and costly when used in the many iterations needed in optimizing the design. This paper presents a set of improved approximate models for the prediction of iron loss. They can be used in design optimization programs and, since they are directly related to machine dimensions and material properties, they also provide quick insight into the effects of design changes. A time-stepped finite-element method is employed to evaluate the iron losses in a range of typical PM machines and the results are used to evaluate the adequacy of the models. The predictions of overall iron losses are then compared with measurements made on two PM motors.     

永磁同步电动机空载铁耗研究

从产生根源出发,对永磁同步电动机空载铁耗进行细致分类。在此基础上,利用有限元法和Bertotti铁耗计算模型,以一台5 k W、3 000 r/min永磁同步电机为例,对正弦波供电永磁同步电动机的空载铁耗分布特性进行分析计算,得到基本铁耗与空载杂散损耗的比例关系以及不同因素所引起的空载杂散损耗分布规律。进而,研究了变频器供电空载电流时间谐波引起的谐波损耗,分析了不同极槽配合对变频器供电永磁同步电机的谐波损耗影响规律。最后,通过多台样机的空载铁耗试验,验证了计算的正确性。     

杂散损耗分离技术用于永磁同步电机高效设计

随着超高性能磁性材料的广泛应用,空调压缩机用变频永磁同步电机的能效已达极致,进一步提升异常困难。目前,电机结构参数优化仍是能效提升的重要技术手段,各项损耗的准确估算及规律的探究则是能效进一步提升的关键。本文针对变频永磁同步电机,系统分析了损耗的分类,提出了损耗配比系数K的概念,用以评价电机电磁设计额定点的效率是否最优;基于K值概念,用FEM法对一款变频永磁同步电动机的结构参数进行了电磁方案再优化,以提升电机能效;设计了基于线性回归的杂散损耗实验分离方法,并对优化前后的样机进行了损耗分离、效率和损耗配比系数的计算,结果表明优化后的电磁方案在额定工况点的损耗配比系数K更接近于1、效率提升显著。     

DETERMINATION OF IRON AND STRAY LOAD LOSSES IN INDUCTION MOTORS USING A THERMOMETRIC METHOD

Abstract

In an induction motor, losses in the magnetic materials account for 10% to 20% of total losses. The iron loss effectively reduces both the output capability and possibly the life span of the machine. To limit these undesirable effects a prior requirement is to accurately assess the iron losses, and understand their nature and, ideally, their spatial location. An experimental method for determining the iron and stray load losses is presented. The test motor is a 3 phase, 4 pole, 4 KW induction motor which was heavily instrumented with thermocouples to map the loss distribution.     

Experimental verification of stray losses in cage induction motors under no-load,full-load and reverse rotation test conditions

Contents The stray load losses of polyphase squirrel-cage induction motors have hitherto rarely been measured at rated voltage and full-load, owing to the great difficulties in achieving the required measuring accuracy; instead, mostly the reverse rotation test is used. This paper primarily deals with the question whether the reverse rotation test yields representative results. It is also examined to what extent it is possible to predetermine the stray losses by means of a series of new investigations on space harmonics of flux density and harmonics of rotor current. For this purpose the stray losses of a four-pole 11 kW polyphase induction machine with semi-closed and open stator slots as well as rotors with a varying number of unskewed and skewed slots are measured under no-load and full-load conditions and in the reverse rotation test and computed for machines with unskewed slots.

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Experimentelle Überprüfung der Zusatzverluste von Käfigläufermotoren im Leerlauf, unter Last und im Reverse Rotation Test

Übersicht Wegen der beträchtlichen meßtechnischen Schwierigkeiten sind die Zusatzverluste von Drehstromasynchronmotoren mit Käfigläufern bisher nur selten bei Nennspannung und Nennlast gemessen worden; statt dessen verwendet man weithin den Reverse Rotation Test. Die vorliegende Arbeit befaßt sich in erster Linie mit der Frage, inwieweit es möglich ist, die Zusatzverluste mit Hilfe einer Reihe neuer Untersuchungen der Oberfelder und Läuferoberströme vorauszuberechnen. Außerdem wird die Gültigkeit des Reverse Rotation Test untersucht. Zu diesem Zweck werden die Zusatzverluste einer vierpoligen 11 kW-Drehstromasynchronmaschine mit halbgeschlossenen und offenen Ständernuten sowie Läufern mit ungeschrägten und geschrägten Nuten unterschiedlicher Nutenzahl im Leerlauf, unter Nennlast und im Reverse Rotation Test gemessen und für Maschinen mit ungeschrägten Nuten berechnet.

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List of symbols B magnetic flux density - f frequency - g order of rotor slot harmonics - I, I ₀,I _n stator current, at no load, at rated load - I _vr harmonics of rotor current - N number of slots - P power - P _Cu fundamentalI ² R losses - P _Fe iron losses at no-load test - P _Fe50 iron losses due to 50 Hz flux density - P _f friction and windage losses - P _gap airgap power - P _m mechanical power output - P _rrt stray load losses at reverse rotation test - P _s electrical power input at stator - P _stray stray losses - P _strayn stray load losses at rated load - P _{stray 0} stray losses at no-load - p number of pairs of poles - q slots per pole and phase - s slip - T torque - U voltage - order of rotor harmonic pairs of poles - order of stator harmonic pairs of poles - supply angular frequency Principal subcripts n at rated load - r rotor - s stator     

A new separate‐identification method of two stator equivalent core‐loss resistances corresponding to hysteresis and eddy‐current losses for parallel‐type mathematical models of AC motors

This paper proposes a new unified method for identifying equivalent stator core‐loss resistance of AC motors, which can be applied to both induction and synchronous motors. In order to realize AC motors that exhibit high performance such as precise torque generation and/or efficient energy transmission, stator core loss cannot be neglected in designing vector control systems. It is common to model stator core loss in magnetic circuits as loss caused by equivalent resistance in electrical circuit. One of the best mathematical models for controlling AC motors with core loss is a kind of parallel‐type model that succeeds in modeling both eddy‐current and hysteresis losses. The newly proposed method succeeds in identifying separately and simultaneously two kinds of equivalent core‐loss resistances on the model corresponding to eddy‐current and hysteresis losses. The practical usefulness of the method is evaluated and confirmed through experiments using two induction motors of 5.5 and 2.0 kW having relatively high core losses and a permanent magnet synchronous motor of 750 W having relatively low core losses. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(4): 50–63, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10152     

Leakage magnetic flux density in the vicinity of induction motor during operation

In this work, the low frequency electromagnetic flux density around induction motors is studied; the main objective is to provide safety regions for humans in the vicinity of these motors, especially in electrical vehicles, where high currents and hence high flux density emissions are expected. A new equivalent magnetic circuit which accounts for stray magnetic fields is developed. The analysis shows that the emission of the stray field in the radial directions depends on the permeability of the stator body as well as the ampere turn of the stator winding. Small values of stator body permeability may result in very high stray flux emissions at levels that may require shielding to protect passengers just above the motor. Relatively far away from the stator (e.g., 50 cm for the tested motors), the flux is normally of low level and may not represent an exposure threat.     

浅谈EH-STAR方法测试附加损耗的实验室应用

世界各国都在致力高效电机的开发,IEC新版标准IEC60034-2-1《确定效率和损耗的试验方法》已获通过,明确取消了按输入功率的0.5%来假定附加损耗的老方法,而使用EH-STAR作为附加损耗的最新测试方法。笔者在该方面首先提出了自己的经验。     

The variation of cage motor losses with skew

A study on the effect of skew on the losses in three different induction motors is presented in this paper. It is shown that skew alters the balance of losses in the motor and that, in larger machines, this can result in an increase in the total losses in the motor.