Effect of internal capacitive compensation for reactive power in induction motor

The effect of the internal capacitive compensation for reactive power in an induction motor is examined. In this motor, the stator winding is a combination of two windings, which play a role of the operating winding of the motor and compensating windings when they are connected according to the circuit of a rotatable autotransformer to electric capacity. If the internal capacitive compensation for reactive power is used, the start-up and operation performances of an induction motor are increased and the engineering and economical performances of the induction motor are improved.     

Unusual PD pulse phase distributions in operating rotating machines

The position of partial discharges (PD) with respect to power frequency phase position has long been known to provide useful information on the nature of deterioration of electrical insulation. In the past, virtually all such data has been from PD tests performed in the laboratory on static models or equipment. Improvements in the past 15 years in noise elimination technology have made it possible to monitor the PD activity (number, magnitude and phase position) in the HV stator windings of operating motors and generators. Over a two year period, the PD activity was recorded on more than 100 motors, hydrogenerators and turbine generators, and the pulses analyzed with respect to the ac phase position, with a resolution of 3.6°. In the majority of stator windings, the PD pulses occurred in the expected portion of the ac phase, i.e. Between 0 and 90° as well as between 180 and 270°. However a significant number of instances were recorded where the pulses appeared to be shifted ~30°. This is probably due to the phase-to-phase electric stress which occurs in the endwinding portion of a three phase stator winding. In many other machines, the PO phase positions were very different from the expected patterns determined from static tests. In some of these cases, such results were obtained on machines with suspected loose stator windings. It seems reasonable to conclude that the unusual PD patterns may be due to the influence of moving stator coils on the PD patterns. Such an influence is not easy to simulate in static laboratory tests. PD pulse phase analysis is shown to be a useful means of helping to determine the main deterioration mechanisms of stator insulation systems of operating motors and generators     

Double Three-phase Induction Machine Modeling for Internal Faults Simulation

Multi-phase induction motors present excellent characteristics for faulty tolerant operation. Among them, six-phase induction motors, which are among the most used, exhibit two types of configuration: the double three-phase and the six-phase with single neutral. The double three-phase presents the advantage of reducing harmonics with its symmetric winding. This article presents a new modeling of the double three-phase induction machine for internal faults simulation. The developed model is composed by two sets of three-phase stator windings forming two stars. The model considers an arbitrary displacement (α) between stator stars, allowing the simulation of this type induction machines with different configurations, with 60° displacement used herein. The simulations of internal faults, such as stator windings or rotor faults, are both considered in the proposed model, allowing the machine study under abnormal conditions. The double three-phase induction machine model was fully implemented in real coordinates, making it possible to simulate stator and rotor faults without being necessary to change system equations coordinate. Several examples allow verifying the characteristics of the proposed model and its application for internal fault analysis. Experimental results are also presented to validate the obtained simulation results.     

Permanent magnet synchronous machines with concentrated coil armature windings: analysis and test validation of Single Stator–Double Rotor,axial flux machines

Some design and operation aspects of axial flux permanent magnet synchronous machines, employing armature windings with concentrated coils wound around the stator teeth, are presented. The e.m.f. control is based on the variation of the windings flux linkage, obtained by modifying the stator (or rotor) configuration. Thanks to the high number of poles and the excellent waveform quality, even with deep field weakening, these machines exhibit a satisfactory operation at low speed, both as generators and motors. In the paper, the main constructive machine features are discussed, together with some design and FEM results. A test on a prototype has also been carried out.     

大功率绕线式异步电机无功补偿装置的研究

阐述了绕线式异步电机的无功补偿原理;建立了d,q,0坐标系的数学模型.通过在绕线式电机转子回路上串接容性电压,以降低电机的无功功率,减小定子侧的电流,提高电机的效率及其过载能力.系统采用单相至三相交-交变频产生容性电压,简化了电路,大大减小了变压器的总容量;采用单片机作为控制核心,使系统具有过流、过温、转子缺相、主电机运行状态监控等保护功能.该系统可广泛用于建材、化工、化肥、造纸、制药、冶金等大中型绕线式异步电机中.     

直流输电谐波不稳定抑制新方法

针对传统直流输电系统中谐波不稳定现象,研究了一种新型换流变压器及其滤波系统。其阀侧绕组采用延边三角形接线,为3倍数次谐波电流提供通路;通过匝比配合,实现12脉波换流;延边绕组与公共绕组构成自耦变压器接线,在公共绕组上连接滤波支路,并调至谐振点,配之以变压器零阻抗设计,在阀侧实现谐波抑制兼无功补偿功能。对拟建立的直流输电开发研究平台在设计参数的基础上,进行了计算机仿真研究,仿真结果表明:新型换流变压器及其滤波系统可大幅降低交流网侧中2、3次非特征谐波与11、13次特征谐波电流含量,很好地抑制直流输电系统的谐波不稳定,同时新系统中的滤波器阻抗在基频下呈容性,其对换流器可进行无功功率补偿,改善了系统的动态稳定性。     

Effect of stator chording and rotor skewing on performance ofreluctance synchronous machine

Low torque ripple in electrical machines is generally required to reduce acoustic noise and mechanical resonance vibration. To design for low torque ripple, however, affects the average torque and the power rating of the machine. In this paper, the effect of stator winding chording and rotor skewing on the average torque, power factor, and torque ripple of the normal laminated, internal flux barrier rotor reluctance synchronous machine is investigated. The two-dimensional finite-element time-step method together with the basic machine equations are used in the analysis. It is shown that to design, in general, for low torque ripple and minimal effect on torque rating of the reluctance synchronous machine, full-pitch stator windings must be used, the rotor must be skewed by a stator slot pitch, and a low number of stator slots must be avoided     

交直流混合供电的三/十二相电机定子漏电抗计算

交直流混合供电的三/十二相电机因其显著的优点将被广泛应用于独立供电系统中,该电机定子上有两套绕组,一套三相绕组提供交流电,另一套十二相绕组整流后提供直流电.该电机定子槽中放置了四层不同线圈的导体,并且多套三相绕组同时工作时的气隙磁势也比普通三相电机复杂得多.利用解析的方法分析了三/十二相电机定子漏电抗的计算,导出了相关的公式,并计算了某三/十二相电机的定子漏电抗参数,利用这些参数计算值,对三/十二相电机的突然短路进行了仿真研究,仿真结果较好地吻合了实际样机的试验结果,验证了所计算的参数值的正确性.     

Completely Superconducting Electric Machine with High Specific Power

The main tendency in transport development is a move toward electric or hybrid propulsion, which is due to the increased requirements relating to the ecological effects and efficiency of transport systems. A key parameter that determines the prospects of electric transport is the specific power of electric machines (generators and motors). Thus, e.g., electric machines with a specific power higher than 20 kW/kg are necessary to produce electrical aircraft. Studies have shown that, during long operation, such magnitudes of specific power can be achieved with the use of cryogenic cooling and modern high-temperature superconductors (HTSCs) in electric motors and generators. In addition, the critical properties of superconductors should be taken into account, which leads to scientific and engineering problems. In particular, the HTSC stator winding should be made of coils in the form of racetracks. This can be done in a machine with a number of grooves per pole and a phase less than unity. In this work, the circuit of such completely superconducting electric machine with high specific power has been considered. The analytical technique of calculations of the main parameters has been suggested. The obtained expressions allow one to analyze the influence of number of pole pairs, superconductor properties, and main dimensions of a machine on the specific power. The results of the finite-element modeling of a completely superconducting electric machine have been considered.     

DEVELOPMENT OF A STATOR-CONTROLLED BRUSHLESS INDUCTION MACHINE WITH LEADING VAR CAPABILITY

ABSTRACT

The use of the DC-component of rotor current to continuously generate large amounts of reactive kVA from the stator of cage-rotor induction machines in which the total line current may be at a leading power factor, has been recently discussed [ 1-3 ] with initial test results from a 35 H.P. unit. The only constructional difference between these space-transient machines and conventional rotary motors is in the stator MMF layout which includes mixing of two wavelengths in operation simultaneously. The rotor current distribution is no longer sinusoidal but contains a series of harmonics similar to those present in a sheet-secondary linear induction motor with a pronounced longitudinal exit-edge effect at high speed. The development of the 35 and 150 H.P. machines which operate at unity power factor on 50?Hz is presented in light of the work performed earlier[4]to neutralize the exit-edge effect in a 17?kW LIM which attained an 80% terminal power factor at 50?Hz by the use of an asynchronous condenser winding of a second pole-pitch smaller than the main stator pole-pitch     

Preservation of large motors and generators from weather onoffshore platforms

The problems encountered with moisture condensation in the bearing cavities and internal windings of large motors and generators when proper equipment storage procedures are not practiced are outlined. The moisture condensation problems associated with the operation and shutdown of large motors and generators due to weather conditions at the site location of the offshore platforms are also discussed. The particular platforms discussed are located on the outer continent shelf in the Santa Barbara Channel off the coast of California. On-site modification of the generator housing and the electrical module was necessary to preserve the electrical equipment from the effects of the weather. The recommended method of preservation and the necessary precautions before the startup of the electrical machines are presented     

电机定子结构及其绝缘介电常数的频率特性对定子绕组电容值的影响

确定电机定子线棒的高频参数对于研究局部放电信号在电机绕组中的传播特性及研究PWM逆变器驱动的交流电机的定子绕组电压分布有重要意义。文中对大型汽轮发电机定子线棒的电容做了比较详细的研究，内容包括：对电机定子线棒复合绝缘等值介电常数的频率特性的测试研究、采用数值计算方法计算出用铝箔纸裹住的电机定子线棒的多导体传输线模型的单位长度电容、线棒股线间薄绝缘对电容的影响、对铁心硅钢片叠片间隙对电容的影响等。其数值计算结果与之前测量得到的电容值比较吻合，这也证明了通过测量开路阻抗、短路阻抗来得到电机定子线棒分布参数的试验方法是有效的。     

含风电场电力系统动态优化潮流的混合蛙跳算法

根据无功补偿就近的原则,风电场尽量不从系统吸收无功,风电场所需无功主要由风电场无功补偿装置提供。考虑发电机的阀点效应和异步风力发电机组无功补偿装置投切的离散性,含风电场的电力系统动态优化潮流属于复杂的多约束混合整数非凸非线性规划问题。计及各个时间断面的耦合性,将所有时段统一进行优化,以整个时段所有常规机组费用最小为目标函数,建立了含风电场电力系统动态优化潮流的数学模型。提出将混合蛙跳（SFL）算法应用到统一考虑所有时段的动态优化潮流计算中,给出了具体实现方法。在改进的IEEE 30节点系统中分别采用SFL算法和粒子群优化算法进行了仿真计算,结果表明所提出的方法是有效的。     

双功率异步电动机节能控制与保护器设计

设计了一种双功率异步电动机的节能控制与保护器.该控制器通过检测负载电流大小来控制电机的两个定子绕组的通断,以提高其负荷率,实现节能;同时对电机进行多种保护,具有操作简单、性能稳定、节能明显等优点.     

Analysis and investigation of size spectrum of synchronous machines operating as wind-power-generators in the range of rotation frequencies of 75–300 rpm

The modern design tendencies of wind power generators based on synchronous machines with permanent magnets have been analyzed. It is shown that it is possible to create a spectrum of wind power generators with tangential magnetic flux and stator concentric windings in the range of rotation frequencies of 75–300 rpm. Some parameters of the developed generators are presented.     

An Energy-Efficient Induction Motor with an Unconventional Electromagnetic Core

In modern power setups of autonomous objects, electromechanical converters with good mass and volume performances are used. However, the problem of lowering the specific energy parameters of electric machines remains important. This article presents new technical solutions and calculation methods for unconventional energy-saving machines with improved mass and volume performances. The electromagnetic core of machines includes a stator winding with active and front conductors of rectangular cross section. The cross section of the jumpers for connections of active and front conductors is reduced. The front conductors of the stator winding do not intersect. These measures make it possible to reduce the consumption of copper, achieving a decrease of the length of the electromagnetic core while maintaining high efficiency. It has been shown that manufacturing such multilayer wavelike windings is promising. The design of the an induction motor with a stator winding of this type has been considered. The technical features in designing electrical machines with a new stator winding are discussed. A detailed end-face scheme of the stator winding and a scheme of the sequence of conductor commutation of this winding are presented. Expressions for calculating the overhang parts of the winding are given. Results of comparison new and serial motors with a power of 75 kW are given.     

A brushless electric motor with a transverse magnetic flux and disk rotor

Brushless permanent magnet machines (BPMMs) have a greater efficiency and smaller overall dimensions than do other types of machines and are widely used in electric drives for various purposes. Two types of BPMMs are used in practice: BPMMs with a classical double-layer-distributed stator winding and BPMMs with a toothed-step stator winding. There exists another type of BPMM with a transverse magnetic flux (transverse flux motors, TFMs) which is being actively studied. In TFM electric motors, the magnetic lines of fluxes of the poles of rotor end perpendicular to the direction of rotor rotation. Stator windings in these machines are fabricated as rings coaxial with rotor, and the magnetic circuit of stator consists of separate fragments. Specialists assert electric TFMs have a higher specific power—the ratio between the output power and the mass of the machine—than the electric motors of other type. They are of interest, first and foremost, for electric drives without reducing gears. In most TFM, only a half of the poles of rotor are magnetically connected with circular phases of stator. In this work, the TFM design with disk rotor is described, in which the magnetic flux of all poles of rotor is coupled to the circular phases of stator. The stator magnetic circuit in this machine consists of P-like elements, and alternation of polarity of these elements is provided due to the change of their position. As a result, the magnetic flux coupled to the circular phase increases doubles, as do the machine torque and power. Some results of modeling of a three-phase electric motor are presented. The results were obtained using the Ansys Maxwell computer code, including a graph of the change of torque on the shaft of a machine under rotation of the rotor under conditions of sinusoidal currents in phases.     

变频调速下异步电机的一种运行效率优化方法

针对异步电机效率优化问题,得出了合理调节电机中的有功功率和无功功率的比例可以使电机的运行效率最大的结论,并探讨了在有功无功功率合理匹配比下的变频调速系统的控制特性,同时指出了功率合理匹配原理与常见的"铜耗等于铁耗,电机效率最大"原理的本质区别.     

Characteristics of a permanent magnet type bearingless motor

Super high-speed and high-power electric machines are required for turbomolecular pumps and spindle drives. High rotational speed and high power drives can be achieved with bearingless motors. In this paper, a bearingless motor with the principles of permanent magnet type synchronous motors is proposed. High power factor and high efficiency can be expected in permanent magnet type bearingless motors. The proposed bearingless motor is a 4 pole permanent magnet synchronous motor, in which additional 2-pole windings are wound together with 4-pole motor windings in stator slots. With currents of 2-pole windings, radial magnetic forces are produced to support a rotor shaft. Principles of radial force production of surface-mounted permanent magnet bearingless motors are analyzed mathematically. It was found that radial forces are efficiently produced by employing thin permanent magnets on the surface of rotor iron core. A test machine was built in order to measure inductance functions as well as relationships between voltages and currents     

隐极同步发电机励磁绕组匝间短路的多回路电感参数计算

为了对故障中各种电气量进行准确仿真分析以揭示隐极同步发电机励磁绕组匝间短路的故障机理,需要准确计算电机的各种参数,尤其是与发生匝间短路的励磁绕组有关的电感参数.从隐极同步电机分布式励磁绕组在各极下的单个同心式线圈出发,应用气隙磁导的概念和谐波分析的方法计算与单个励磁线圈有关的电感参数,并按照故障的励磁绕组的实际连接情况进行叠加,得到了与励磁绕组各回路有关的多回路参数模型.该模型考虑了励磁绕组故障回路产生的各种谐波磁场的作用,并通过具体算例间接说明了其合理性.将该参数模型用于励磁绕组匝间短路故障的多回路计算,计算结果与样机实验吻合,验证了参数模型的准确性.