外文翻译(交流电气化铁路牵引系统).doc

兰州交通大学毕业设计英文文献翻译（原文）AbstractIncreasing attention has been shown in recent years in the a.c. electrification of railway traction systems and a number of established systems now exist throughout the world. Where the traction system is supplied directly from a high-voltage national-grid network, a common component of such schemes is a step down transformer connection between the two systems. The electrical, mechanical and thermal design of these transformers is subject to a number of special considerations not normally encountered in the design of distribution-type transformers of similar rating and voltage class. The paper reviews the operating conditions peculiar to railway traction such as over voltages, short circuits, cyclic and peak loadings and discusses how these conditions influence the design and construction of single-phase transformers supplying power for traction purposes. The paper describes the engineering practice and operating experience obtained with the British 25 kV a.c. railway-traction system in particular, but much of the system and transformer-design philosophy and operational experience referred to applies to a.c. traction systems elsewhere in the world.Key Words: Power transformers, Railways, Traction- I -兰州交通大学毕业设计英文文献翻译（中文）1 IntroductionIn March 1956 the British Transport Commission announced their intention to adopt a 25 kV single-phase 50 Hz a.c. system as the standard for future electrification of British Railways in all Regions except the Southern, where extension of the existing third-rail system, which had been operating satisfactorily for some years, was considered to be the most satisfactory course to follow.The commission had earlier authorized a study to be made of the comparative costs of electrification at 1500 V d.c. and at 25 000 V single-phase 50 Hz a.c. This showed both economic and technical advantages in favor of the a.c. system, and the decision was taken to adopt it. Another decisive factor was the successful operational experience gained by the French Railway Authorities from an experimental line, installed a few years earlier in North Eastern France, operating at the same voltage and frequency.It was consequently decided to adopt a 50 Hz a.c system to introduce it on the Scottish, Eastern and London Midland Regions. 25 kV was chosen as the general standard for main-line services and 6-25 kV as a subsidiary standard for use in those areas, mainly suburban, where it was not practicable to modify existing structures, such as tunnels and overhead bridges, which at that time imposed restrictions on the electrical clearances to live conductors.As a result of operational experience, 625 kV systems are now being converted to 25 kV, and it is visualized that eventually this will be the operating voltage for all regions.This paper reviews the operating conditions peculiar to railway traction, resulting from over voltages, short circuits, cyclic and peak loading, and discusses how these conditions influence the electrical, mechanical and thermal design and construction of the single-phase transformers supplying power for traction from the National Grid system to British Rail at 25 kV 50 Hz a.c. Although the paper describes British practice in particular, much of the system and transformer design philosophy and operational experience referred to is applicable to systems elsewhere in the world.2 System data2.1 Supply to the railway-track feeder stationsBulk supplies are taken from the 132 kV and 275 kV grid systems via single-phase traction-supply transformers and fed to the feeder stations at 25 kV. The feeder stations are located adjacent to the rail tracks at 40 or 50 km intervals, and wherever possible in close proximity to grid substations to avoid the disadvantage of long feeders. On the first Regions to be electrified, supplies were taken in duplicate, but on recent extensions to the North Western and Eastern Regions a single transformer has been provided at every alternate supply point, and the possibility of installing only one transformer in future at each substation is now being considered.A typical two-transformer installation is illustrated in Fig. 1. The 25 kV traction supply is taken to the feeder-station bus bars either by concentric 2-core oil-filled underground cables or by single-circuit wood-pole overhead lines. One feeder-station bus bar supplies current to the overhead-contact system and a separately mounted bus bar is connected by sheathed cable to the track running rail, which, by virtue of the overhead line supporting structure bonded to it, is well earthed.The duplicate supplies to the bus bars are separated by a section switch which is normally open, and each circuit supplies an up and down section of the track. When outages are necessary, for maintenance or emergency operation, the section switch at the supply point is closed. The remaining transformer must be capable of feeding the whole length of the section of the track normally fed by two transformers. The designed rating of the transformer must therefore be adequate to cater for the maximum demand under this emergency condition. This demand may occur at any time of the year, in either summer or winter conditions, therefore the thermal rating of the transformers must be adequate to ensure winding and oil temperatures do not exceed the guaranteed maximum under the prevailing ambient temperature. 3. System operational factors3.1 Load currentThe load-current demand on a traction-supply point installation is of a highly fluctuating pattern and is no sinusoidal in waveform. The current fluctuations are random in time and magnitude and depend upon the density of traffic within the section of traction circuit supplied by the transformers and upon the mode of operating the locomotives. The no sinusoidal current, Fig. 2, is of approximately square waveform and occurs by reason of the harmonics generated by the rectifier equipment on the locomotives.The significance of this type of load-current duty upon the design aspects of the transformer is of particular relevance when considering the rating of the transformer, the effect upon regulation and the mechanical forces acting on the windings.Fig. 3 represents a typical load-current-demand curve obtained on a supply-point transformer. The maximum variation of current can be between zero and two and a half times the full-load rated value. The combined heating effect on the transformer windings of a current varying in this manner, and having the typical no sinusoidal waveform referred to, is greater Fig.1Typical 25 kV 2-transformer power-supply installationSupply authority supply railway authority supply:(a) 132/33kV 3-phase area-board transformers (b) 132/25kV single-phase railway-supply transformers (c) Supply-authority circuit breakers (d) Railway-authority circuit breakers (e) Concentric cables or overhead lines (f) Pilot cables for protection, telecommunication and supervisory duties .than that which would be produced by a steady current having a value equal to mean value of the fluctuating current, although both would indicate equal MW readings on the half-hour integrated maximum-demand meters.Correlation of typical supply-current-demand curves, obtained during measurements under both normal and emergency supply-point operation, indicates that if a transformer is to cater for the worst expected load condition without exceeding temperature-rise limits, the equivalent rating has to be some 1 -2 to 1 -3 times the expected circumstances. The varying magnitude of the load current also has an effect upon the integrated half hourly maximum demand for the particular operating mechanical strengths of the transformer windings. In service, the windings are subjected to pulsating forces similar, in many respects, to those experienced by Fig.2One cycle of typical 25 kV and 50 Hz traction voltage and currentrectifier and arc-furnace-supply transformers. These forces can have deleterious effects on the performance of the windings and associated insulation in service, unless measures are taken in the design and construction of the transformer to ensure that they can be withstood.Fig.3Typical traction load-current-demand curve3.2 Harmonics and unbalanced current effectsDuring the development of the railway single-phase traction system, one of the main characteristics, to which particular attention was given, was the question of single-phase unbalanced loads and harmonics imposed on the 3-phase supply system. The harmonic effects arise as a result of the rectification equipment installed on the locomotives. 123 From the many investigations which have been made on the system, it has been shown the grid-supply system is large enough to absorb these effects without significant interference to other consumers or generating plant. It will be remembered, however, that the early development of the system was in urban and industrial areas where the fault levels were very high. In rural areas, such as the west coast extension between Manchester and Glasgow, and where lower fault levels prevail, conditions are marginal and provision for the later addition of harmonic filters has been made should these be required.4.1 Transformer design General specificationThe traction-supply transformers are of core-type construction and are designed, manufactured and tested in accordance with BEB Specification T2 and CEGB Specification RT (1971), BS171 and other national specifications which may be relevant. Any special requirements are specified in pertinent contract documents.4.5 Considerations affecting the choice of transformer constructionThe paper has outlined the different methods of construction which have been generally adopted to meet the requirements determined by factors arising from consideration of the system or test. It is believed these designs are of equal merit in providing the best overall economic and technical advantages and this has largely been confirmed by experience.An alternative form of construction, often considered in the context of railway transformers or other applications where a high degree of inherent mechanical strength is required to withstand short-circuit forces, is that of the shell-type construction. In this method of construction, the h.v. and l.v. windings are interleaved axially, thereby avoiding radial forces, the only force component being in the axial direction. As the windings are largely contained within the core window, the core yokes provide solid points from which to brace the windings against movement in the axial direction. From this aspect alone, the design could be considered superior to those already described.In other aspects, however, the shell-type transformer presents decidedly uneconomic disadvantages. By reason of interleaving the h.v. and l.v. windings, shell-type transformers have an inherently low reactance and the geometry of the windings would have to be adjusted at the expense of space factor to achieve an impedance of 10% on 15 MVA. Also, because of the 2-pole simultaneous-impulse-test requirement, the electrical clearances at the centre of the coil stack height to the surrounding core would have to be adequate to withstand approximately twice the applied impulse-test voltage. Other considerations are the need to minimize eddy-current losses in the windings, by means of conductors having a low axial profile, and the transposition of the conductors if wound in parallel in the axial direction. Design studies have shown this form of construction is not economically viable when compared with the core-type construction, particularly at supply voltages of 132 kV and above, and the greater expense involved is not believed to be justified in the light of what has been achieved with the existing designs.摘 要近年来，对交流电气化铁路牵引系统和现在它在全世界存在数量的关注已越来越多。直接由国家高压电网为牵引系统供电的关键一步是一个连接两个系统之间降压变压器。这样的变压器在设计时旨在考虑一些电气，机械和热特性等一些特殊的因素，而不是通常所说的在分布式变压器的设计中所考虑的类似电流等级和电压等级等的因素。本文阐述了铁路牵引运营过程中出现的如过压，短路，周期性出现的过负荷等特有的现象并讨论这些现象将如何影响为牵引而供电的单相牵引变压器的结构设计。本文特别介绍了在英国的25kV交流铁路牵引系统中获得的工程实践和运营经验，但许多提到的系统和变压器的设计理念和运作经验适用于世界其他地方的交流牵引系统。关键词：电力变压器，铁路，牵引- VII -兰州交通大学毕业设计英文文献翻译（原文）1引言英国运输委员会在1956年3月宣布他们的打算，就是采用25kV，50Hz的单相交流系统作为英国所有地区未来的英国铁路电气化标，除南方，因为南方延用了当时现有的铁路系统并已令人满意的经营了好多年，被认为最好的铁路系统是沿用当时的铁路系统。早些时候，委员会曾授权进行了一项比较1500V直流电气化和25k V，50Hz单相交流电气化的成本的研究,这项研究表明25k V，50Hz单相交流电气化系统在经济和技术先进方面都占优势，并做出了采用这种系统的决定。由法国铁路当局从几年前在法国东北部建成的在相同的电压和频率运营的试验线获得成功的运作经验是另一个决定性因素。因此决定采用50Hz的单相交流系统，并引进到苏格兰，东欧和伦敦中部地区。25kV作为主线服务的一般标准，6-25kV在这些由于当时带电导体的电气间隙的强制限制导致的修改现有的结构并不可行的区域（主要是郊区），如隧道和高架桥梁，作为附属标准使用。作为一个运作经验的结果，6-25kV系统被转换为25 kV作为所有地区的工作电压是可以实现的。本文综述铁路牵引由于过压，短路电流，周期性出现的过负荷造成的特有的运营条件，并讨论这些条件将如何影响由英国国家电网的以25kV，50Hz交流电源供电的英国铁路的单相牵引变压器的电气，机械和热特性及结构的。虽然本文特别介绍了英国的实践，但是这个系统的很多东西、变压器的设计理念和上面提到的运营经验在世界的其他地方也适用。2系统数据2.1对铁路轨道供电臂的供电大部分供应是132kV和275kV电网通过单相牵引变压器向25kV的供电臂供电。馈电所设置在离钢轨40或50公里的地方，并尽可能接近电网变电站以避免长馈线的缺点。在首次实现电气化的地区，电供应采取了一式两份的供应方式（什么意思？），但最近在西北部和东部地区的扩展，单台变压器已在每个备用供应点被供应，并且在以后每个变电站只安装一个变压器的可能性正在被考虑。一种典型的双变压器安装说明如图1所示，这种25kV的牵引供电通过同心充油式两芯地下电缆或单回路木杆式架空线路传送到馈电所母线。一个馈电所母线提供电流到架空的接触网和一个单独安装的母线通过铠装电缆连接到工作的轨道上，如果通过架空线支持结构连接它，它会更好的接地。图1典型的25千伏变压器安装电源供电局供应铁路局供电：(a) 132/33 kV 三相变压器；(b) 132/25 kV单相变压器；(c)供电局的断路器；(d) 铁路局的断路器；(e) 连接导线或者架空线；(f) 起保护通信和监督作用的同心电缆。对母线重复供电被分段的常开开关隔离的，每个电路供应一个轨道的上下段。当为了维修或紧急的操作而需要断电时，在这个供电点的分段开关闭合。余下的变压器必须有能力为这个区段整个长度的通常是通过双变压器供电的钢轨供电。因此，变压器的设计等级必须能足够应付这种紧急情况下的最大需求条件。这种需求可能会出现