Corona in high voltage rotating machine windings

An understanding is provided of the phenomena that take place in the windings of turbine generators, water wheel generators, and large motors. The steps that are normally taken by a manufacturer to alleviate this type of electrical aging are reviewed     

振动分析在电力设备状态检测中的应用和发展

综述了振动分析技术在电力设备状态检测中的应用及其研究现状,包括发电机、感应电动机、变压器和断路器。评述了基于振动信号分析的电力设备状态检测、故障诊断的主要研究方法,同时指出小波理论和神经网络在发展新的状态检测技术中具有非常重要的作用。     

热缩材料在变电设备上的应用

电气设备运行中污闪、小动物、覆冰闪络、凝露闪络等事故产生的后果是非常严重的.随着城乡电网建设及改造的大幅度增加,探讨如何从技术上解决污闪、小动物、覆冰闪络、凝露闪络等事故是非常必要的.对于热缩材料在变电站电气设备上的应用,以及使用过程中出现的施工和运行上的问题进行了探讨.经过几年的实际运行,证明高分子热缩材料在变电设备上的应用大大减少了事故的发生.     

Motor Contribution During Three-Phase Short Circuit Fault

One of the major factors to be considered in selecting the ratings of electrical equipment (circuit breakers, bus bar bracing, etc.) is the level of three-phase short circuit current available at the equipment location in the system. The total three-phase short circuit current at a faulted point includes both the currents from the power source (such as electric utility company or in-plant generators) and contribution from electrical motors in the system. Presently, the calculation of three-phase fault current in a system is based on the method outlined in IEEE Standard 141-1976 in which the calculation of motor contribution within the system is defined. It will be pointed out that during a three-phase fault, only motors directly connected to the faulted bus or downstream buses will contribute fully to the fault. Other induction motors (with transformers connected between the motors and the fault) may or may not contribute current to the fault point. These motors will continue to receive power from the supply and act as motors. Therefore lower fault current values will be the result. This finding will have a significant bearing on borderline equipment selection with consequent savings in equipment cost. The conclusion is drawn that the calculated short circuit current based on IEEE Standard 141-1976, is higher than the actual value. This leads to unnecessarily high fuse and breaker interrupting ratings, bus bracing, etc. Computer studies and an analysis of this phenomenon are presented.     

Control strategy for an icebreaker propulsion system

The latest series of Canadian Coast Guard ice-breakers features a diesel electric propulsion system using synchronous motors and synchronous generators. The synchronous generators supply power to a constant-voltage 60 Hz bus that feeds the ship's hotel load and the propulsion system's cycloconverters. The cycloconverters convert 60 Hz AC power to variable frequency 0-18 Hz AC power for the synchronous propulsion motors. The propulsion motors are directly connected to the ship's propellers by means of shafting. This AC-AC propulsion system realizes the `power plant' concept, which optimizes the number of generators that are online in order to match the generated electrical power to the total electrical demand of the ship. The propulsion control system has two control loops that limit the power delivered by the propulsion motors to prevent the diesel engines, which drive the generators, from stalling during instantaneous or sustained overloads     

A Unique Solution to Improving Motor Winding Life in Medium-Voltage Motors

It has been recognized for years that electrical motors installed in petrochemical plants require protection from condensation. Papers have compared different methods of preventing condensation from collecting in 600-V motor windings. These papers covered the advantages of directly heating the motor windings by introducing a low-voltage ac or dc source to the windings when the motor is not running. Their conclusion was that low-voltage heating. is the most practical solution to motor moisture problems since the heat is evenly distributed throughout the stator windings and does not cause hot spots in the windings as conventional motor heaters can. Many installations in recent years have proven the reliability of this low-voltage application to windings. A case history is given of retrofitting a newly developed motor windings heater to an existing 5000- hp 2300-V synchronous motor that has had numerous winding failures due to moisture. The installation is at ARCO Chemical Company's Port Arthur, TX, plant.     

利用一次电流检验电流互感器二次回路的方法

利用一次电流检验电流互感器二次回路接线正确性,是新设备投入运行前必须进行的一项基础工作,应针对不同的元件采取不同的方法。结合现场试验实例,分别论述了发电机短路电流、小型电流发生器、外加电压、利用容性电流和负荷电流、大型电机启动电流和变压器的励磁涌流等一次电流检验电流互感器二次回路方法的特点及其适用范围,可供工程人员参考。     

Practical experiences of on-line partial discharge measurements ona variety of medium-voltage electrical equipment

In recent years, there has been a considerable amount of discussion concerning partial discharge (PD) measurements on medium-voltage motors and generators. If one considers the total plant electrical distribution system and production equipment, motors comprise only a small part of the plant electrical equipment. If a motor should fail, part of production will likely be shut down and there will be lost revenue. However, there is a wide variety of other equipment in a facility, besides a motor, that can fail and can have a much more devastating effect on the plant's production. Additional items to consider for PD monitoring are the plant incoming transformers (they may be owned by the plant if the plant is purchasing primary power), the incoming switchgear, cables, bus duct, other remote substation switchgear, and power center transformers. Methods have been developed to monitor PD in all types of medium-voltage equipment. This paper discusses application of sensors, methods of measurement and data interpretation and present several case studies     

Electric Drives (Boldea, I and Nasar, S.A.; 2006) [Book Review]

The new enlarged second edition of this excellent textbook presents the latest concepts and basic electrical drive technology including vector and direct torque control of ac motors and generators. Some of the topics covered in the book's 15 chapters include: energy conversion in electric drives; electric motors for drives; power electronic converters for drives; dc brush motor drives; controlled rectifier dc brush motor drives; synchronous motor for drives; PM and reluctance synchronous motor drives; switched reluctance motor (SRM) drives; practical issues with PWM converter motor drives, large power drives, and an entirely new chapter on control of electric generators. Each chapter is supplemented with adequate, well-selected examples, summary, problems, and selected references at the end. An important advantage is an attached CD that includes test browsing, PowerPoint slides, and Matlab-Simulink programs with eight selected dc and ac closed-loop drives. The book is recommended as a basic text to a wide audience of engineering educators, students, and engineers in industry.     

Partial discharge theory and technologies related to medium-voltageelectrical equipment

Partial discharge (PD) monitoring is an effective online predictive maintenance test for medium-voltage (MV) motors, MV generators, and MV switchgear at 4160 V and above, as well as other electrical distribution equipment. The benefits of online testing allow for equipment analysis and diagnostics during normal production. Corrective actions can be planned and implemented, resulting in reduced unscheduled downtime. An understanding of the theory related to PD, and the relationship to early detection of insulation deterioration is required to properly evaluate this predictive maintenance tool. This paper presents a theory to promote the understanding of PD technology, as well as various implementation and measurement techniques that have evolved in the industry. Data interpretation, corrective actions, and application to electrical distribution equipment is also reviewed     

Update: offshore electrical installation practices

As the search for oil and gas progressed, platforms were located further offshore in deeper waters. This necessitated the requirement for offshore living quarters located on the platforms. Thus, the generation of electricity became a natural part of the scene on most platforms as the requirements grew to include cooking, heating and air conditioning, and lighting requirements for living quarters. This article discusses the development of electricity systems for offshore platforms form the 1950s to the 1990s. The development of the American Petroleum Institute's recommended practices (API RP) to cope with the unique design and installation requirements of the electrical systems is discussed. Revisions to the API RP 14F in the areas of power generating stations, distribution systems, electric motors, lighting, battery powered DC systems, and special systems are also discussed     

Evaluating the Effects of Motor Starting on Industrial and Commercial Power Systems

The motors being applied on modern industrial systems are becoming increasingly large in size. Starting these large motors, especially across-the-line, will produce a transient voltage depression that can substantially reduce the motor output torque while severely influencing the operation of any locally connected load, as well as loads served by buses electrically remote from the point of motor starting. Motors with special starting characteristics and reduced voltage starting equipment may reduce motor inrush and the associated voltage dip, but the starting performance of the motor may be unacceptably altered. How computer aided studies are of benefit in exploring the problems associated with starting large motors on industrial systems is discussed. Several types of studies that are presently available are described, and the data or information required to perform these studies are reviewed. Finally the results that can be expected from a motor starting study effort are examined.     

Analogs and characteristics of compensated asynchronous machines with different numbers of phases

The disadvantages of three-phase asynchronous motors with short-circuited rotors, which are widely used in practice, are discussed. It is determined that the most significant disadvantage is consumption of two types of electric energy from a network: active energy for conversion into mechanical energy accompanied by inevitable heat losses and reactive energy that is not converted into other types of energy, but is expended on generation of the magnetic field required for electromechanical conversion of energy in an electrical machine. It is suggested to use internal capacitive compensation of reactive power to improve the technical and economic indices of asynchronous machines of both motors and generators. In addition, each phase winding of the asynchronous machine stator is divided into two parts equal in number of turns spatially shifted between each other in the core slots by an angle of 30°. These parts are connected according to the scheme of the rotary autotransformer to the electrical capacity at its output. The change of the spatial position of the stator windings leads to a change in time of the action of the phase angles of their electromotive force and, therefore, of currents and voltages without changing the introduced reactive impedances. Thus, the spatial coordinate of the electrical value is converted into the time coordinate in the electromagnetic circuit with a rotating magnetic field. The combination of this property of the stator windings in accordance with the rotary autotransformer with the action of the electrical capacity at its output creates the effect of internal capacitive compensation of reactive power in an asynchronous machine. The ability to use internal capacitive compensation of reactive power in single-phase asynchronous machines is considered. A method of calculation of the characteristics of compensated asynchronous machines taking into account the change of the magnetizing contour resistance is presented. The advantages of compensated asynchronous motors and compensated asynchronous generators are determined. Recommendations as to their effective practical use are given.     

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.     

What's the real cost of higher efficiency? [electrical energy efficiency]

The problems that California had with electrical energy have only emphasized the need to look at the true cost of high-efficiency energy devices used by cement plants since electrical energy is among the top expenses in producing cement. This article focuses on low-voltage induction motors and lighting systems. Low-voltage induction motors generally account for about 30% of the electrical energy consumed by a cement plant. Lighting systems generally account for about 3-5% of the electrical energy consumed by a cement plant, but it is a fixed load that does not directly contribute to production. Life-cycle cost analysis is used to determine the true costs of this equipment. True equipment cost is defined as the total of the initial capital expenditures plus the operating costs, which include energy and maintenance. Even though the foremost requirement for a piece of equipment is its performance in the production chain, the justification for selecting one piece over another should be based upon the initial capital cost plus operating expenses. A review is given of two selected areas of electrical equipment to test their cost of ownership.     

High-speed electrical machines for power engineering: Current state and development trends

The current state of high-speed electrical machines with shaft rotation velocity within the range of 10 000 to 50 000 rpm is considered and the development trends are analyzed. The analysis includes recent publications and the results of the authors’ studies. Data of the developed motors and generators are presented. Forecasts regarding directions in the development of high-speed electrical machines are made.     

Harmonic filtering for the offshore industry

The application of a large number of adjustable speed drives (ASDs) operating electric submersible pumps (ESPs) on two separate offshore platforms, connected to a limited electrical power system on a tanker feeding power to the platforms via subsea power cables, presents technical problems involving high levels of harmonic distortions that experience shows can impact the overall system reliability. Such a system is described and discussed in detail and practical solutions to the problems are illustrated. The design of the harmonic filters are shown to have a major impact on the overall operation of the power system     

人工智能技术在交流异步电机故障诊断中的应用

电机是实现电能转换的核心设备,用于驱动各种生产设备,其连续安全运行直接影响着国民经济及社会发展。异步电机应用广泛,运行工况多样,其故障诊断备受关注。对异步电机故障诊断的重要性以及存在的主要问题进行了分析,总结研究了近年来人工智能技术应用于该领域的最新进展,并提出了后续关注的重点方向和工作。     

DETERMINATION OF HEAT STATE OF NORMAL LOAD INDUCTION MOTORS BY A NO–LOAD TEST RUN

ABSTRACT

Determining the nominal thermal conditions of Induction Motors (IM) experimentally requires the appropriate equipment for loading the motor, expending the electrical energy and an enormous amount of time, The difficulties of these tests increase with the size of the motors and when it is necessary to perform the tests at the place of installation. This paper discusses the heating process of induction motors in a no–load test run under normal and over–voltage conditions. The method of prediction and recounting the results of a no–load test of IM on a full load run is proposed. The theoretical research of heat processes into IM is based on its thermal circuit and its electrical equivalent. Some of the parameters of the equivalent circuit were determined from the experiment. The influence of the technological uncertainties of manufacturing IM on their thermal parameters is also discussed.     

AC Induction Motor Torsional Vibration Consideration?A Case Study

Much has been written on the application of high-speed (3600 r/min) motors to pumps and compressors relative to vibration and lateral critical speeds. A reciprocating compressor coupled to an induction motor is a complex torsional system and can present a more complex set of problems to the equipment suppliers because of the wider range of forcing frequencies present. The problems encountered on a specific application with the objective of developing guidelines to be used to avoid similar system torsional problems on the application of induction motors to reciprocating equipment are discussed.