Methods for the control of large medium-voltage motors: application considerations and guidelines

Starting and control methods available for medium-voltage (MV) induction motors (2.4-7.2 kV) in the petrochemical industry are continually changing in terms of application considerations due to the evolution of available products and changing characteristics of the machine and processes. This paper summarizes several common methods and provides application guidelines for proper choice selection considering the distribution system, driven equipment, speed-torque issues, process requirements, starter method limitations, and economics. Starting means reviewed include MV soft starters, variable-frequency drives, and autotransformer, capacitor, reactor, captive transformer, across-the-line controllers, as well as fluid couplers.     

Operating temperature considerations and performancecharacteristics for IEEE 841 motors

This paper reviews the operating temperature considerations and performance characteristics for totally enclosed fan-cooled motors as covered in the IEEE 841-2000 motor standard. NEMA MG-1-1998 motor standards are also included since they are embodied in the IEEE standard. Although the scope of product covered is for AC squirrel-cage induction motors through 500 hp, the material presented has application with many other sizes and types of motor. The paper reviews this standard as it applies to the motor operating temperature and various performance characteristics. The impact of temperature on the stator winding, rotor cage, bearings, lubrications, as well as the effects on motor efficiency and other applicable life factors, are considered     

Safety considerations for the application, installation, operation,and maintenance of industrial AC induction motors

Hazardous conditions that can cause serious damage to equipment and create unsafe conditions for personnel are identified. The study is limited to industrial AC induction motors, even though much of it is appropriate to other types of electric motors. The discussion covers: motor selection; hazardous locations; arctic duty motors; lifting means; lifting accessories; mechanical guarding; high-potential testing; non-explosion-proof terminal boxes; motor controls and electrical accessories; motor starting; shaft loading; torsional vibration and stress; transient torques; and transient voltages and currents     

Application considerations for class-1 div-2 inverter-fed motors

Application considerations for fixed-speed motors utilized in hazardous locations are not new to the electrical community and have been discussed previously and are relatively well known in the petroleum industry. Documented guidelines for these applications are currently established, are primarily centered on motor-temperature-rise limitations and the use of nonsparking fans in class-1 division-2/zone-2 locations. However, there are additional considerations when motors and their associated loads are on inverter supply. Items such as the effect on motor temperature rise when operating at reduced speeds for units without independently powered blowers, the effect of nonsinusoidal supply at the motor terminals on motor temperature rise as well as rotor voltage related phenomenon are relevant items. This paper identifies and provides guidelines particular to inverter-fed applications for class-1 division-2 installations.     

Design procedure for switched-reluctance motors

Some of the design aspects of the switched-reluctance motor for nonservo applications are considered. Towards this objective, a step-by-step procedure is developed for the design of switched-reluctance motors     

Some considerations on torque ripple suppression in reluctance motors

Although the reluctance motors are attractive from the standpoints of simple construction and drive electronics, the relatively high torque ripple and acoustic noise are major drawbacks. These drawbacks limit motor applications. In this paper, the torque ripple suppression of the reluctance motor under the sinusoidal current drive is examined. The analysis shows that the torque ripple is caused by the spatial harmonics of inductance. One approach is based on the compensation current generated with the spatial harmonics of inductance. Another is based on the modification of rotor tooth configuration to eliminate the spatial harmonics. According to the proposed strategies, torque ripple suppression characteristics can be evaluated at the design stage of the motor. Both approaches have been verified by experiments. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 118–128, 2000     

Improved designs of disk induction motors of block-module type for extreme environments

The construction of new disk induction motors of block-module type, which are a part of motor-transformer units (MTUs), are considered. The induction motors are intended for operation in hermetic objects under extreme conditions: a gas, steam-to-gas, and liquid environment at high pressures (up to 150MPa) and temperature (up to +600°C). The primary winding of the transformer part of the unit is connected to a three-phase network, and the secondary z-phase bar winding is located in Z grooves of the magnetic conductor of a transformer closed on one side by a short-circuited ring. The motor part of the unit contains an induction motor with a short-circuited rotor and stator with bar uninsulated winding connected to the transformer secondary winding; on the opposite side, it is closed by a short-circuited ring. The induction motor can be implemented with a disk short-circuited rotor located between two disk stators with bar windings. The bars of the transformer secondary winding are connected with Z bar-shaped hermetic lead-ins installed in a hermetic partition. Each bar-shaped hermetic lead-in is connected at the other end with n bars of the stator winding through intermediate conductive arc-shaped segments adjoining the stator. The operating principle and operation features of new disk induction motors of block-module type are considered.     

电励磁同步电机无源性控制系统研究

无源性控制是基于能量观点的一种全局定义且全局稳定的控制策略,对参数变化及外来扰动有较强的鲁棒性,是一种本质上的非线性控制.本文建立了同步电动机基于欧拉—拉格朗日方程的机电统一数学模型,在模型中分离出不影响稳定性的无功力,并在此基础上设计无源性控制器.这种控制器不仅形式简单、无奇异点,而且无需转子阻尼绕组电流观测器.仿真和实验验证了无源性控制器能够很好地实现期望的跟踪控制目标,证明了该控制策略的有效性.     

基于无源性的感应电机控制系统设计

感应电机的无源性控制方法从能量的角度分析电机控制系统,具有形式简单、无奇异点、鲁棒性好等特点.本文给出了感应电机的欧拉方程并将感应电机系统分解为电气和机械两个无源子系统的反馈并联,从而说明在设计控制器时只需要考虑电气子系统,简化了控制算法.在此基础上,利用无源性控制原理,设计了电机的转矩和转速控制器.该控制算法具有全局稳定,系统鲁棒性较好的特点.仿真和实验结果均证明了用此算法构成的感应电机控制系统能很好地跟踪速度给定,具有较好的动静态响应能力.     

高压电机用新型玻璃粉云母带性能及应用的研究

为了满足高压大型发电机定子线棒主绝缘发展的要求，研制了特5440-1桐马环氧玻璃粉云母带，经检测该粉云母带的性能、线棒电气性能以及试样线圈常态耐久性试验全部合格；经用户应用试验表明：将特5440-1粉云母带用于高压电机其质量指标达到JB56082-1996部颁质量分等优等品标准要求。     

Transformer design and application considerations for nonsinusoidalload currents

The use of adjustable-speed drives requires transformers capable of withstanding high levels of harmonic currents under normal operating conditions. Experience has been that overheating problems are much more common with dry-type transformers than with liquid-filled transformers. Transformer insulation life is determined by the hot spot temperature but confirmation of hot spot temperature rise is one performance characteristic which is ignored in industry standards. This is especially important for transformers rated for nonsinusoidal load currents. The design of transformers for nonsinusoidal load currents should include an analysis of the eddy loss distribution in the windings and calculation of the hot spot temperature rise. Calculations and thermal tests giving only average winding temperature rises are not sufficient. Thermal tests with nonsinusoidal currents and measurements of hot spot temperature rises are extremely difficult on large transformers. The combination of testing and analysis may be the only economically practical approach. Analysis indicates that the dry type transformer hot spot temperature is very sensitive to the eddy loss magnitude and distribution. The Underwriters Laboratories Inc. (UL) K-factor rated dry type transformer and the recommended practices given in ANSI/IEEE C57.110 are reviewed. When purchasing transformers subject to nonsinusoidal load currents, considerations should be given to the manufacturer's development program and capability to calculate the eddy loss distribution and hot spot temperatures     

Design techniques for reducing the cogging torque in surface-mounted PM motors

Several techniques may be adopted in designing surface-mounted permanent-magnet motors in order to reduce the cogging torque. This paper describes various classical and innovative techniques, giving a theoretical justification for each of them. To this aim, a simple original model of the cogging torque mechanism and a Fourier analysis are introduced. As a result, it is highlighted that some techniques are not always utilizable, and some of them may even be deprecatory when not used correctly. In addition, effects of cogging torque elimination on back electromotive force are discussed.     

三相无刷直流电动机分数槽集中绕组槽极数组合规律研究(连载之五)降低永磁无刷直流电动机齿槽转矩的设计措施

降低齿槽转矩通常是永磁电机设计的主要目标之一.综述了永磁无刷直流电动机齿槽转矩的主要设计措施,包括采用分数槽绕组、优化磁极极弧宽和槽口宽、不等气隙、斜极和斜槽、磁极分段错位、磁极偏移、齿顶开辅助凹槽等,可供设计者参考.     

Design considerations for Arctic grounding systems

Grounding information and design guides are presented for use in Arctic design which will comply with the intent and letter of the National Electrical Code (NEC), be economic, and will not result in excessively conservative designs. It is concluded that the proposed grounding practice without a widespread conventional ground grid appears to be adequate and in compliance with the NEC. This method is also cost-effective, resulting in significant savings. Where step and touch potentials are a likely problem, ground planes in the form of grids or platforms are still recommended. A high-resistance ground system is desirable from the point of view of reduced step and touch potentials     

Design of low-torque-ripple synchronous reluctance motors

A design approach oriented to the minimization of torque ripple is presented for synchronous reluctance motors of the transverse-laminated type. First, the possible types of rotors are classified and the more suited rotor structure is evidenced, to be matched to a given stator. Then, the inner rotor design is described, pointing out the low-ripple measures. Lastly, experimental results are given from three different rotors; they confirm the validity of the proposed approach     

Proper application of motors operated on adjustable frequencycontrol

Most high-efficiency motors can withstand the rigors of adjustable speed drive (ASD) operation. However, there are significant differences between applications of motors operated on sinewave power and motors operated on adjustable frequency controls (AFCs). This is an ongoing subject, rapidly changing due to advances in the technology of the AFCs. Subsequently, many of the older problems associated with the application of motors on AFCs have been solved, while at the same time, new problems were introduced. In many cases, high-efficiency, low-voltage motors can be applied on AFCs with no or little modification. In order to do this successfully, however, basic motor operating principles and the affect of applying a motor on an AFC need to be understood. The proper application of a motor for use on an ASD is dependent on an understanding of: thermal motor limitation-from AFC harmonics and reduced-speed operation at constant load (i.e., constant torque); and upper-speed limitation (beyond base speed)-constant power electrical limitation and mechanical upper-speed limitation. This article targets the application of motors not specifically designed for AFC operation. Generally, NEMA motors (i.e., motors up to the 440 frame) are more apt to be indiscriminately applied on AFCs than above-NEMA (ANEMA) motors (i.e., motors larger than the NEMA frame sizes). The concepts/guidelines presented here are equally applicable to both NEMA and ANEMA motors     

Design considerations for the switched reluctance motor

Analytical design equations are developed to predict the performance and to guide the design of the switched reluctance motor (SRM). The use of these analytical equations to trade-off different SRM attributes is discussed. The various approximations and simplifications used in the development of the analytical design equations are justified using results obtained from a detailed computer model of the SRM and by using experimental results from a high power density SRM designed for an aircraft engine fuel pumping application. Comparisons of predicted and measured machine performance parameters for this 90 kW 25000 r/min machine, such as flux linkage curves, back EMF, electromechanical power converted, and inverter voltampere requirements are presented. It is also shown that there exists a fundamental maximum torque density that is attainable with the SRM and an estimate of this maximum torque density limit is given. The power factor for an SRM is defined and the machine parameters that determine its value are presented. This power factor is compared to the similarly defined power factor for an AC machine and found to be smaller     

Design considerations for high-frequency coaxial winding powertransformers

The use of coaxial windings to create low-loss, low-leakage-reactance, power transformers for use in high-frequency soft-switched DC/DC and resonant converters has been demonstrated by M.H. Kheraluwalest al. (1990). Some of the important loss aspects of the design of coaxial winding transformers are examined, including the influence of the skin effect on winding resistance, the variation of core loss caused by nonuniform core flux density, and the choice of the principle dimensions and aspect ratios for maximum efficiency. Experimental measurements on a 50 kVA, 50 kHz unit are included to confirm portions of the analytical results and suggested design procedures