Effects of converter pulses on the electrical insulation in low and medium voltage motors

A new IEC test specification is under development for the insulation systems used in converter-driven machines with the aim of providing manufacturers with a reliable means to quality insulation systems for use in converter-fed machines and users with confidence that the machines they purchase contain insulation that is fit for their intended purposes. Much of the qualification testing for insulation systems subject to converter voltages may be undertaken with existing 50/60 Hz equipment. However, for testing of complete coils in low voltage machines, an impulse generator and an impulse PD test set are required. For large machines, which have stress-graded endwindings, it will be necessary for a source of converter voltage to be available.     

The use of doubly fed reluctance machines for large pumps and wind turbines

Brushless doubly fed induction machines (BDFIMs) have been extensively researched over because of the possibility of using a partially rated inverter in many applications with limited speed variations. However, the special cage rotor construction and substantial rotor losses is one of the key deficiencies of these machines. A similar and extremely interesting machine, the brushless doubly fed reluctance machine (BDFRM), has been largely ignored in comparison. This was mainly due to the fact that reluctance rotor designs were not capable of generating saliency ratios large enough to make the BDFRM competitive with other machines. However, developments in reluctance rotors, spurred on by research into synchronous reluctance machines, have resulted in high-saliency-ratio cageless rotors that are economical to build. This, together with the promise of higher efficiency and simpler control compared to the BDFIM, means that further investigation of the BDFRM is warranted. This paper presents a comparative theoretical analysis and aspects of practical implementation of the important control strategies and associated machine performance/inverter size tradeoffs for the BDFRM in the light of its most likely applications-large-pump-type adjustable-speed drives and variable-speed constant-frequency wind power generation systems.     

无刷双馈电机基于同步角的矢量解耦控制

无刷双馈电机(BDFM)特殊的结构特点,可以大大降低调速系统的容量,使其在调速系统中有着巨大的潜能.在同步参考系的矢量解耦数学模型基础上,分析研究了BDFM基于同步角的矢量解耦控制.采用这种控制方法,使BDFM的矢量控制变得与普通异步电机的矢量控制一样简单,能用于调速性能要求较高的调速系统.     

Now That's Smart!

This article describes the features and development of intelligent machines and concentrates on their information processing infrastructure. IEC 61499 function blocks have been used in these experiments as the driving vehicle to achieve important features of the intelligent machines such as reconfigurability. Information infrastructure of intelligent machines is based on the IEC 61499 architecture . The function block architecture of IEC 61499 provides a new degree of flexibility in managing embedded control and information processing systems through the lifetime of industrial automation products. The requirements of flexible manufacturing and material handling systems, such as rapid integration and reconfiguration, as well as the growing information intensity of the production environments imply that manufacturing equipment is becoming more autonomous and intelligent.     

Restructuring an electric Machinery course with an integrative approach and computer-assisted teaching methodology

The course of Electric Machinery has been one of the core courses in the Electrical Engineering (EE) curriculum at Texas A&M University-Kingsville (TAMUK). In the past, the course was designed to focus mainly on topics of transformers and electric machines and was typically presented under the assumption of steady-state conditions. Unfortunately, many students considered the course old-fashioned and unexciting, and this lack of interest, in turn, seriously limited their ability to understand and appreciate the wide-ranging applications of electric machines. More important, electric machines today have become widely integrated with power electronics, digital signal processing (DSP), and digital control technology. However, these technological changes were not adequately reflected in the traditional teaching structure of the course. This paper presents a new approach that, by integrating computer-assisted teaching methodology in classroom presentation, substantially restructures the course so that it provides a comprehensive treatment of electric-drive systems with discussions covering electric machines, power electronic converters, feedback controls, power supply systems, and mechanical systems.     

Assessing Test Data

Online partial discharge (PD) testing has been used for more than half a century to provide useful information for diagnosing and monitoring the integrity of stator winding insulation of large generators and motors. Interest in online PD detection and monitoring has as the technology, which was originally used on machines rated higher than 10,000 V, has expanded its application to the smaller, lower-voltage (e.g., 4,160 or 6,900 V) machines. However, questions remain on how to assess stator insulation problems using PD test data. This article documents the most recent developments in research and applicable guides and standards related to online PD monitoring on rotating machines.     

An Algorithm for Determining the Technical Condition of an Electric Machine

One of the main factors determining the efficiency of the operation of a modern vessel is the technical condition of electric machines used as drives for various mechanisms in the marine equipment. Evaluation of the current technical state of electric machines is a critical task in the general problem of process management in the system of marine-equipment maintenance and repair, the performance of which is connected with revealing partial malfunctions in the equipment and further operational failures. This article studies one of the algorithm options for processing the time series of the regulated parameters of the electric machines, which allows predicting the time frames for their maintenance according to their actual state in order to prevent a failure. The relevance of this approach is substantiated by the fact that switching to the technology of maintenance based on evaluation of the technical state of marine equipment, systematic observation, and operability prediction implemented using automated onboard measurement and regulation systems (among which are also diagnostic systems) is an efficient way of ensuring reliability of marine equipment.     

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.     

无刷双馈电机的一种矢量解耦控制

无刷双馈电机(BDFM)调速系统可以大大降低调速装置的容量,在大功率调速系统中有着广阔的应用前景,但由于缺乏有效的控制策略,阻碍了其应用和推广,因此迫切需要新型的控制策略来改善其性能,以扩大其应用范围。在同步参考系的矢量解耦数学模型基础上,利用同步角和转矩的关系,提出了一种简单实用的矢量解耦控制,采用这种控制方法,使BDFM的矢量控制变得与普通感应电机的矢量控制一样简单,能用于调速性能要求较高的调速系统。     

The effect of automatic voltage regulation on the bifurcationevolution in power systems

This paper discusses the relationships between types of bifurcations in power systems and their expected occurrence for voltage regulated and unregulated synchronous machines. A time-scale decomposition is performed to identify critical dynamics in the slow and fast subsystems. For single machine systems, the existence of an unstable limit cycle prior to Hopf bifurcation is analysed in the context of the region of attraction     

Decentralized two-level excitation control of multimachine power systems

A two-level decentralized scheme for the excitation control of multimachine power systems is presented. The control strategy is based on decomposing the control signal for each machine into two components generated by controllers at two different levels. At the first level, controllers are designed to optimize the performance of each generating unit, totally ignoring the couplings among the machines. The second control components are chosen to reduce the machine performance degradations due to the presence of interactions. With the developed two-level control scheme each machine is controlled entirely from its own state. The effectiveness of the proposed approach is illustrated by a numerical example involving a four-generator system.     

MICROPROCESSOR BASED NONLINEAR EXCITATION CONTROLLER FOR SYNCHRONOUS MACHINES

ABSTRACT

The synchronous machines in power systems have the excitation systems of field winding to improve the transient stability of power systems. The synchronous machines are nonlinear systems, however, the excitation systems have been designed based on linearized systems, because the stability analysis of nonlinear systems is difficult and the generalized control method of nonlinear systems has not been developed yet.

This paper proposes a nonlinear excitation controller for synchronous machines in power systems. For the sake of simplification of the nonlinear state feedback control, this paper considers both the transient stability and the suppression of the rotor swings in transient conditions. The effect of the automatic voltage regulator (AVR) for the synchronous generator is not discussed here. This controller is designed based on Lyapunov's direct method that can directly judge the stability of nonlinear systems. The usefulness and validity of the proposed excitation controller are confirmed by numerical simulations and experiments. The microprocessor based generator excitation system that consists of a nonlinear controller, state variable detector, and PWM inverter, is constructed. The nonlinear excitation controller can improve the transient stability of synchronous machines.     

Comparative performance of open and totally enclosed machines

Continuous improvements in insulating materials, manufacturing consistencies in sealed windings and extensive laboratory testing of various systems show that synchronous machines with NEMA II construction can replace totally enclosed machines. Tests on windings in corrosive atmospheres show that sealed insulation systems are impervious to the environment. Standard maintenance ensures that incendive arcing will not be generated in potentially hazardous environments. When compared to totally enclosed machines, the NEMA II-type construction is lighter, more efficient, has lower short-circuit current and associated torques and is easier to maintain     

Progress in roller press design technology

Since the introduction of roller press technology to the cement industry in the mid eighties, its range of application and the capacity of the machines used has increased significantly. Roller presses are now being supplied with throughput capacities of over 1000 mtph for clinker and cement raw material processing with drive capacities of 3000 kW. As roller press technology continues to gain acceptance for the closed circuit finish grinding of cement processes and products, this trend will undoubtedly continue. Realizing this need, several significant design changes and developments have taken place to allow the construction of larger, more reliable machines. These developments were essential if the machine was to be able to meet the ever-increasing process demands being made upon it. This paper discusses the most significant of these advancements for large roller press design, and in particular discuss the state of the art design for the following major components: roller design, new autogenous wear surface; bearing design; bearing housing/roller alignment; bearing oil lubrication; and the hydro-pneumatic system. The paper concludes by briefly discussing how these design advancements will influence future roller press application possibilities as related to the US cement industry     

The Potential for High Temperature Superconducting AC and DC Motors

ABSTRACT

The prospect of using superconductivity (SC) to power electrical machines has been a tantalizing but elusive goal ever since its discovery by Onnes in 1911. However, recent developments which have raised the critical temperature above liquid nitrogen (77K) has removed the major obstacle to practical application of SC to rotating machinery, namely the liquid helium refrigerant system. This paper addresses the potential for utilizing high temperature superconductivity (HTSC) in rotating (as opposed to linear) electrical motors and discusses several approaches to their implementation. Although SC at liquid nitrogen temperature is assumed, the implications of SC at room temperature is not considered in this paper.     

The improvement of the electrical insulation of high voltage electrical machines

Comparative parameters are presented for the electrical insulation systems of high voltage electric machines. Composite insulation materials produced by different manufacturers are studied. The influence of the structure and composition of electrical insulation materials on the main operation parameters (electric strength, dielectric losses, the mechanical characteristics, and resistance to thermal cycling) of the insulation systems of electric machines is shown.     

Corona deterioration reduction in large electrical machineinsulation

Partial discharge or corona activity in the insulation system of large electric machine stators has caused deterioration of these machines, and in some cases resulted in premature failures. Development work is being done to better understand the cause and effects of this corona activity. Efforts are centering around the increased use of corona-resistant material, and the reduced use of corona-sensitive materials. Some of the developments are described in this paper     

电力系统小干扰稳定性研究的新进展

叙述了电力系统小干扰稳定性分析和控制方面已有的研究成果和新进展,评述了它们的机理和适用性。结合我国电力系统结构和运行特点,提出了小干扰稳定性分析和控制研究需进一步开展的工作。     

Analysis of terminal voltage waveform of AC exciting synchronous generators

Recently, adjustable speed hydroelectric power systems have been developed. In those power systems, ac exciting synchronous generators are used instead of the ordinary salient-pole-type synchronous machines. However, some higher harmonic sequences are included in the distribution of air-gap magnetic flux density and in the terminal voltage waveform of the ac exciting synchronous machines because these machines have open winding slots. To develop better machines without terminal voltage waveform distortions, an evaluation method of the terminal voltage harmonics has been needed. This paper describes the mechanism of higher harmonics generation qualitatively and proposes an analytical method of no-load terminal voltage waveforms on the basis of two-dimensional magnetic field analysis considering movement of the rotor for quantitative higher harmonics analysis. The analytical results of higher harmonics show good agreement with the experimental ones.     

无刷双馈电机的矢量解耦控制方法

无刷双馈电机(BDFM)特殊的结构特点,可以大大降低调速系统的容量,使其在调速系统中有着巨大的潜能.在国内外对BDFM研究的基础上,分析了目前在BDFM的闭环控制中基于同步参考系数学模型的矢量控制策略的实现.尽管标量控制可以用于低性能的调速系统,但迫切需要新型的控制策略来改善其动态性能,以扩大其应用范围.采用矢量解耦控制是一种有效可行的方法.