外文翻译(交流电气化铁路牵引系统).docx

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1、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

2、 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. T

3、he 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

4、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 transform

5、ers, Railways, Traction第 7 页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-

6、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 bot

7、h 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, operat

8、ing 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 subur

9、ban, 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

10、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 desi

11、gn 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

12、 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

13、 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 t

14、ransformer 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

15、 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 over

16、head 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

17、 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.

18、 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 factors

19、3.1 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

20、 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 aspect

21、s 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 c

22、an 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 a

23、uthority 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, telecommun

24、ication 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, o

25、btained 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 var

26、ying 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 c

27、ycle 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

28、 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

29、 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 a

30、bsorb 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 Manc

31、hester 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. Transformer design General specificationThe traction-supply transformers are of core-type construction and are designed,

32、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 constructionT

33、he 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 advantag

34、es 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 constru

35、ction. 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

36、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-

37、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 coi

38、l 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 condu

39、ctors 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 th

40、e 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与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，机械与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与电压等级等的因素。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构造设计。本文特别介绍了在英国的25kV交流铁

41、路牵引系统中获得的工程实践与运营经历，但许多提到的系统与变压器的设计理念与运作经历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，委员会曾授权进展了一项比拟1500V直流电气化与25k V，50Hz单相交流电气化的本钱的研究,这项研究说明25k V，50Hz单相交流电气化系统在经济与技术先进方面都占优势，并做出了采用这种系统的决定

42、。由法国铁路当局从几年前在法国东北部建成的在一样的电压与频率运营的试验线获得成功的运作经历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，东欧与伦敦中部地区。25kV作为主线效劳的一般标准，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构造并不可行的区域主要是郊区，如隧道与高架桥梁，作为附属标准使用。作为一个运作经历的结果，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

43、路的单相牵引变压器的电气，机械与热特性及构造的。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、变压器的设计理念与上面提到的运营经历在世界的其他地方也适用。2系统数据对铁路轨道供电臂的供电大局部供给是132kV与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防止长馈线的缺点。在首次实现电气化的地区，电供给采取了一式两份的供给方式什么意思？，但最近在西北部与东部地区的扩展，单台变压器已在每个备用供给点被供给，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

44、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与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构造连接它，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给铁路局供电：(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) 起保护通信与监视作用的同心电缆。对母线重复供电被分段的常开开关隔离的，每个电路供给一个轨道的上下段。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

45、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在一年的任何时间，无论是夏季或冬季，因此，变压器热性能必须足够好以确保绕组与油温度不超过当时的环境下保证的最高温度。3 系统运行因素负载电流图2典型的25 kV，50Hz牵引电压，电流的一个周期图3典型的牵引负载电流的需求曲线现在牵引供电所用的牵引电流是高度波动且不是正弦波形的电流。目前的电流波动是随机的且非常严重，且电流的波动取决于每一个由变压器与处于运行模式的机车构成的牵引回路的区段的交通密度。当考虑变压器的电压等级时，这种类型的负载电流说明的及变

46、压器设计方面有很大的关系，主要是作用在绕组上的调控与机械力的影响。图3代表了一种典型的在变压器上获得的负载电流需求曲线。电流最大变化可以在零与两点五倍的满负荷额定值之间变化。电流在这种形式变化的变压器绕组产生的叠加在一起的热效应与上面提到的具有典型的非正弦波波形，是大于，这将是产生一个稳定的与波动电流的有效值相等的电流值，虽然它们都有一样的MW读数。在正常与应急供电操作下，测量获得的典型供电电流的需求曲线说明如果一个变压器是为了应付在最坏预期的负载条件下不超过温升限值，相当于电压等级是预期特定的操作系统的情况下每半小时的最大需求的到倍。负载电流的最大变化对变压器绕组的机械强度有影响。在工作中，

47、绕组受到类似脉动的力，在许多方面，由整流器与电弧炉供电的变压器已经经历了。这些力可以对工作中的绕组与设备的绝缘性能有有害影响，除非在变压器的设计与施工采取措施以确保它们能够承受这些有害影响。谐波与不平衡电流的影响在铁路单相牵引系统开展过程中，其中需要特别注意的主要特点之一是单相的不平衡负载问题与三相供电系统的谐波问题。作为安装在机车上整改设备的结果，谐波的影响出现了。从在这个系统做的许多调查说明电网供电系统在无明显干扰其他消费者或发电厂情况下面足够承受这些影响。然而我们知道早期开发的系统是在故障水平非常高的城市与工业区。在农村地区，如西曼彻斯特与格拉斯哥之间的低故障率的海岸深处地方，目前的谐波

48、过滤器供给已经取得了这些需求。4 变压器设计4.1 一般种类牵引供电变压器是核心构造，并按照BEB标准T2与CEGB标准RT1971BS171被设计、制造与测试，也可能是其他国家的相关标准。任何特殊要求在合同文件中被指定要求。考前须知影响变压器构造的选择本文概述了已普遍采用的不同施工方法，以满足为系统或测试考虑所产生的需求。鉴于最正确的整体经济与技术优势，这些设计被认为都是一样的优点，这在很大程度上被经历证实。在短路情况下，牵引变压器或其他应用设备往往需承受高度的固有机械强度，在这种情况下，构造的另一种形式，壳式建筑，被考虑。在这种构造模式下，h.v.与l.v.绕组在轴向分力方向设置，从而交织

49、防止径向力。由于绕组大局部包含在核心窗口内，负载对在轴向方向的运动。单从这方面，这个设计可以那些已经描述过的进展特殊考虑。然而，在其他方面，壳式变压器呈现出不经济的缺点。通过h.v.与l.v.绕组相互作用的原因，壳式变压器有一个固有的低电抗器且在以空间因素为代价来实现10的阻抗15MVA，绕组的几何形状将不得不进展调整，此外，由于两极同步脉冲测试的要求，由线圈堆栈中心到周围的核心的电气间隙高度将足够承受大约两倍脉冲测试时施加的电压。其他考前须知是需要采用具有低轴剖面导线与平行导体换位去尽量减少在绕组上的涡流损耗。设计研究说明，及核心型构造进展比拟时，这种构造形式不是经济可行的，特别是在电源电压为132kV及以上的情况下，及已经实现的设计相比，会产生更大的难以置信的花费。