外文翻译-变压器

1、中英文对照翻译原文：TRANSFORMERTransformers come in many sizes. Some power transformers are as big as a house. Electronic transformers, on the other hand, can be as small as a cube of sugar. All transformers have at least one coil. Most have two although they may have many more.The usual purpose of transforme

2、rs is to change the level of voltage. But sometimes they are used to isolate a load from the power source.TYPES OF TRANSFORMERSStandard power transformers have two coils. These coils are labeled PRIMARY and SECONDARY. The primary coil is the one connected to the source. The secondary is the one conn

3、ected to the load. There is to no electrical connection between the primary and secondary. The secondary gets its voltage by induction.The only place where you will see a STEP-UP transformer is at the generating station. Typically, electricity is generated at 13,800 volts. It is stepped down to dist

4、ribution levels, around 15,000 volts. Large substation transformers have cooling fins to keep them from overheating. Other transformers are located near points where the electric power is used. TRANSFORMER CONSTRUCTIONThe coils of a transformer are electrically insulated from each other. There is a

5、magnetic link, however. The two coils are wound on the same core. Current in the primary magnetizes the core. This produces a magnetic field in the core. The core field then affects current in both primary and secondary.There are two main designs for cores:The CORE type has the core inside the windi

6、ngs.The SHELL type has the core outside.Smaller power transformers are usually of the core type. The very large transformers are of the shell type. There is no difference in their operation, however.Coils are wound with copper wire. The resistance is kept as low as possible keep losses low.IDEALIZED

7、 TRANSFORMERS Transformers are very efficient. The losses are often less than 3 percent. This allows us to assume that they are perfect in many computations.Perfect means that the wire has no resistance. It also means that there are no power losses in the core.Further, we assume that there is no flu

8、x leakage. That is, all of the magnetic flux links all of the turns on each coil.EXCITATION CURRENTTo get an idea of just how small the losses are, we can take a look at the EXCITATION CURRENT. Assume that nothing is connected to the secondary. If you apply rated voltage to the primary, a small curr

9、ent flows. Typically, this excitation current is less than 3 percent of rated current.Excitation current is made up of two part is in phase with the voltage. This is the current that supplies the power lost in the core. Core losses are due to EDDY CURRENTS and HYSTERESIS.Eddy currents circulating in

10、 the core result from induction. The core is, after all, a conductor within a changing magnetic field.Hysteresis loss is caused by the energy used in lining up magnetic domains in the core. The alignment goes on continuously, first in one direction, then in the other.The other part of the excitation

11、 current magnetizes the core. It is this magnetizing current that supplies the “shuttle power”. Shuttle power stored in the magnetic field and returned to the source twice each cycle. Magnetizing current is quadrature (90 degrees out of phase) with the applied voltage.1. INTRODUCTIONThe high-voltage

12、 transmission was need for the case electrical power is to be provided at considerable distance from a generating station. At some point this high voltage must be reduced, because ultimately is must supply a load. The transformer makes it possible for various parts of a power system to operate at di

13、fferent voltage levels. In this paper we discuss power transformer principles and applications.2. TOW-WINDING TRANSFORMERSA transformer in its simplest form consists of two stationary coils coupled by a mutual magnetic flux. The coils are said to be mutually coupled because they link a common flux.I

14、n power applications, laminated steel core transformers (to which this paper is restricted) are used. Transformers are efficient because the rotational losses normally associated with rotating machine are absent, so relatively little power is lost when transforming power from one voltage level to an

15、other. Typical efficiencies are in the range 92 to 99%, the higher values applying to the larger power transformers.The current flowing in the coil connected to the ac source is called the primary winding or simply the primary. It sets up the flux in the core, which varies periodically both in magni

16、tude and direction. The flux links the second coil, called the secondary winding or simply secondary. The flux is changing; therefore, it induces a voltage in the secondary by electromagnetic induction in accordance with Lenzs law. Thus the primary receives its power from the source while the second

17、ary supplies this power to the load. This action is known as transformer action.3. TRANSFORMER PRINCIPLESWhen a sinusoidal voltage Vp is applied to the primary with the secondary open-circuited, there will be no energy transfer. The impressed voltage causes a small current I to flow in the primary w

18、inding. This no-load current has two functions: (1) it produces the magnetic flux in the core, which varies sinusoidally between zero and m, where m is the maximum value of the core flux; and (2) it provides a component to account for the hysteresis and eddy current losses in the core. There combine

19、d losses are normally referred to as the core losses.The no-load current I is usually few percent of the rated full-load current of the transformer (about 2 to 5%). Since at no-load the primary winding acts as a large reactance due to the iron core, the no-load current will lag the primary voltage b

20、y nearly 90. It is readily seen that the current component Im= I0sin0, called the magnetizing current, is 90 in phase behind the primary voltage VP. It is this component that sets up the flux in the core; is therefore in phase with Im.The second component, Ie=I0sin0, is in phase with the primary vol

21、tage. It is the current component that supplies the core losses. The phasor sum of these two components represents the no-load current, orI0 = Im+ IeIt should be noted that the no-load current is distortes and nonsinusoidal. This is the result of the nonlinear behavior of the core material.If it is

22、assumed that there are no other losses in the transformer, the induced voltage In the primary, Ep and that in the secondary, Es can be shown. Since the magnetic flux set up by the primary winding，there will be an induced EMF E in the secondary winding in accordance with Faradays law, namely, E=N/t.

23、This same flux also links the primary itself, inducing in it an EMF, Ep. As discussed earlier, the induced voltage must lag the flux by 90, therefore, they are 180 out of phase with the applied voltage. Since no current flows in the secondary winding, Es=Vs. The no-load primary current I0 is small,

24、a few percent of full-load current. Thus the voltage in the primary is small and Vp is nearly equal to Ep. The primary voltage and the resulting flux are sinusoidal; thus the induced quantities Ep and Es vary as a sine function. The average value of the induced voltage given byEavg = turnswhich is F

25、aradays law applied to a finite time interval. It follows thatEavg = N = 4fNmwhich N is the number of turns on the winding. Form ac circuit theory, the effective or root-mean-square (rms) voltage for a sine wave is 1.11 times the average voltage; thusE = mSince the same flux links with the primary a

26、nd secondary windings, the voltage per turn in each winding is the same. HenceEp = pmandEs = smwhere Ep and Es are the number of turn on the primary and secondary windings, respectively. The ratio of primary to secondary induced voltage is called the transformation ratio. Denoting this ratio by a, i

27、t is seen thata = = Assume that the output power of a transformer equals its input power, not a bad sumption in practice considering the high efficiencies. What we really are saying is that we are dealing with an ideal transformer; that is, it has no losses. ThusPm = PoutorVpIp primary PF = VsIs sec

28、ondary PFwhere PF is the power factor. For the above-stated assumption it means that the power factor on primary and secondary sides are equal; thereforeVpIp = VsIsfrom which is obtained = aIt shows that as an approximation the terminal voltage ratio equals the turns ratio. The primary and secondary

29、 current, on the other hand, are inversely related to the turns ratio. The turns ratio gives a measure of how much the secondary voltage is raised or lowered in relation to the primary voltage. To calculate the voltage regulation, we need more information.The ratio of the terminal voltage varies som

30、ewhat depending on the load and its power factor. In practice, the transformation ratio is obtained from the nameplate data, which list the primary and secondary voltage under full-load condition.When the secondary voltage Vs is reduced compared to the primary voltage, the transformation is said to

31、be a step-down transformer: conversely, if this voltage is raised, it is called a step-up transformer. In a step-down transformer the transformation ratio a is greater than unity (a1.0), while for a step-up transformer it is smaller than unity (a1.0)，同样的，一个升压变压器的变比小于1(a1.0)。当a=1时，变压器的二次侧电压就等于起一次侧电压。

32、这是一种特殊类型的变压器，可被应用于当一次侧和二次侧需要相互绝缘以维持相同的电压等级的状况下。因此，我们把这种类型的变压器称为绝缘型变压器。显然，铁芯中的电磁通形成了连接原边和副边的回路。在第四部分我们会了解到当变压器带负荷运行时一次侧绕组电流是如何随着二次侧负荷电流变化而变化的。从电源侧来看变压器，其阻抗可认为等于。从等式 = a中我们可知= a并且=。根据和，可得和的比例是 = = 但是Vs / Is 负荷阻抗ZL，因此我们可以这样表示Zm (primary) = 这个等式表明二次侧连接的阻抗折算到电源侧，其值为原来的倍。我们把这种折算方式称为负载阻抗向一次侧的折算。这个公式应用于变压器的

33、阻抗匹配。4. 有载情况下的变压器一次侧电压和二次侧电压有着相同的极性，一般习惯上用点记号表示。如果点号同在线圈的上端，就意味着它们的极性相同。因此当二次侧连接着一个负载时，在瞬间就有一个负荷电流沿着这个方向产生。换句话说，极性的标注可以表明当电流流过两侧的线圈时，线圈中的磁动势会增加。因为二次侧电压的大小取决于铁芯磁通大小，所以很显然当正常情况下负载电势没有变化时，二次侧电压也不会有明显的变化。当变压器带负荷运行时，将有电流流过二次侧，因为Es产生的感应电动势相当于一个电压源。二次侧电流产生的磁动势会产生一个励磁。这个磁通的方向在任何一个时刻都和主磁通反向。当然，这是楞次定律的体现。因此，所

34、产生的磁动势会使主磁通减小。这意味着一次侧线圈中的磁通减少，因而它的电压将会增大。感应电压的减小将使外施电压和感应电动势之间的差值更大，它将使初级线圈中流过更大的电流。初级线圈中的电流的增大，意味着前面所说明的两个条件都满足：（1）输出功率将随着输出功率的增加而增加（2）初级线圈中的磁动势将增加，以此来抵消二次侧中的磁动势减小磁通的趋势。总的来说，变压器为了保持磁通是常数，对磁通变化的响应是瞬时的。更重要的是，在空载和满载时，主磁通的降落是很少的（一般在）1至3%。其需要的条件是E降落很多来使电流增加。在一次侧，电流在一次侧流过以平衡产生的影响。它的磁动势只停留在一次侧。因为铁芯的磁通保持不变

35、，变压器空载时空载电流必定会为其提供能量。故一次侧电流是电流与的和。因为空载电流相对较小，那么一次侧的安匝数与二次侧的安匝数相等的假设是成立的。因为在这种状况下铁芯的磁通是恒定的。因此我们仍旧可以认定空载电流相对于满载电流是极其小的。当一个电流流过二次侧绕组，它的磁动势（）将产生一个磁通，于空载电流产生的磁通0不同，它只停留在二次侧绕组中。因为这个磁通不流过一次侧绕组，所以它不是一个公共磁通。另外，流过一次侧绕组的负载电流只在一次侧绕组中产生磁通，这个磁通被称为一次侧的漏磁。二次侧漏磁将使电压增大以保持两侧电压的平衡。一次侧漏磁也一样。因此，这两个增大的电压具有电压降的性质，总称为漏电抗电压降

36、。另外，两侧绕组同样具有阻抗，这也将产生一个电阻压降。把这些附加的电压降也考虑在内，这样一个实际的变压器的等值电路图就完成了。由于分支励磁体现在电流里，为了分析我们可以将它忽略。这就符我们前面计算中可以忽略空载电流的假设。这证明了它对我们分析变压器时所产生的影响微乎其微。因为电压降与负载电流成比例关系，这就意味着空载情况下一次侧和二次侧绕组的电压降都为零。电力变压器是电力系统的主要组成部分，它可以实现高效率、低电压损耗的电能传输。由于功率与电压和电流的乘积成正比，所以，在恒定的功率下，（由于低功率损耗和低电压降）提高电压，可以保持低电流水平。电力变压器用于对电能的生产、传输、分配和利用中将交流

37、电压和电流转换成为电力所的适当水平。在1885年由William Stanley 改进的一台经济实用的变压器，使得交流电力系统比直流电力系统更加具吸引力。交流电力系统通过变压器克服了直流电力系统中诸如负载量和传输距离的增高得电压问题。如今的新式电力变压器，在其额定值达到以及超出1300MVA时，将近达到100的效率。本章我们将复习基本的变压器理论并详细阐述在正弦稳态条件下，实用变压器运行的等效电路。我们来看单相双绕组、三相双绕组和三相三绕组的变压器模型，还有自耦变压器和可调变压器。在变压器等效电路中通过略去理想变压器绕组来简化电力系统分析的子系统。在本章中也有介绍，且在剩余的文本中都有用到。电

38、力公司在购买变压器时如何辨别其质量因为变压器是由几个移动部分构成的无源装置，很难逐个地评价它们的质量。但如今，当变压器的使用成本损耗远远超过起初购买它的价格，且购买变压器的一个重要因素就是把那些不能用的元件给替换掉。电力公司需要一种机械装置来权衡不同的制造者所提供的电力变压器，而这些变压器在实际投产之前常常很好。电力和配电变压器，对以评价质量著称的购买工程师来说，提出了完全不同的问题。电力变压器一般是定做的，但如果它们经常和公司以前买的大不相同。电力变压器应该很宽范围的质量参数来评价，而且它们现在经常和公司以前所购买的大不相同。电力变压器应该根据很宽范围的质量参数来评价，而它们每一个都有不同的

39、重要性和重量，这取决于它们的购买效用。比较来说，配电变压器是成组购买的，由于保持了提供的详细的故障记录，可以从计算机统计程序中很容易地决定质量。低损耗意味者高质量工程师所赞同的一个观点是高质量的变压器也是低损耗的变压器。这就意味着，在变压器使用的前几年，高质量的变压器的成本是由损耗的降低来自动补偿的。这样就使如今变压器的使用年限远远长于几年前研制出来的变压器。损失可以分为负载损耗和空载损耗，可以用不同的公式或者计算程序来评估它们的使用响应。当各公司将他们所使用的变压器的成本因素输入到公式里时，所计算出的使用响应将大不相同。例如，估算出的空载和负载的损失比率可以由于一个因素的出现而存在10倍的差

40、别。相关的负载和空载的损失成本也可以因为管制的压力推动公司管理强调不同的需要而每年都有所不同。噪音成为在选择变压器时越来越重要的因素。当然这个因素因为公用程序的不同而变化很大。对一个的低噪音变压器的最大需要是在高度开发区那里子电站与居民区离得很近。变压器噪音有三个来源：（1）铁心的磁致伸缩变形，（2）由制冷器发出的空气动力噪音，（3）从油电路泵中发出的机械流动噪音。铁心发出的噪音，有120HZ的音调，是最难降低也是变电站附近居民抱怨最大的一种噪音。幸运的是，提高铁心建设技术和低损耗铁心钢铁都是为了降低变压器核心的噪音。需要进一步降低铁心噪音，只有通过提高铁心的交叉阶段区域来降低通量密度，这种设

41、计把提高变压器的建设成本转变为降低铁心的损失。然而，达到了降低转换点时增大铁心尺寸的成本，将会超过降低损失的节余。因为一个电力变压器一般必须在确保槽箱中没有油的情况下被拆卸运输，所以安装费是很重要的。如今，是制造商在指定的地点安装起来并填充满而不是留给电力公司。这就保证了变压器的正确安装，而且将失去的部份费用，误会等减到最少。制造设备为产品质量提供了一个关键的说明。大多数的电力公司把评估成套设备作为他们评价过程的第一步。设备更新应该包括制造商的质量保证工程，在职的和可靠性测试报告，合同管理和定单支持，还有技术力量。涂层系统，尤其是对装有缓冲器的变压器，由于变压器的油箱的使用寿命可能是变压器寿命

42、的限制性因素。在不同的制造商之间评价和比较装有缓冲器的变压器的涂层系统的问题随着ANSI 标准的引进而减少。这是一个不支配那些制造商该怎样涂层变压器的机能标准，但是它限制了一系列的测试，以使涂层必须经得起那几个标准。伴随电线杆式变压器标准正在发展中。标准设置的测试包括：刮掉仅有的金属，向其上面喷射盐长达1500个小时，刮掉穿过影线来检查其附着性，在113下暴光的湿度，用没有油漆的碎片、油、紫外电阻及3000圈的磨损电阻来冲击160 in-lb。为了响应这个标准，许多制造商已经修改或改造了它们的油漆过程从表面的准备工作到雷管的运用，到完成涂料方式。现在大多数前进中的油漆过程都采用了电解积贮金属的

43、方法，不论是伸出过程或是用油漆作为一个干能灌，这些过程不仅保证了变压器油箱的每一部分有相同的涂料方式，而且，因为它们淘汰了传统的溶剂油漆，也比较容易满足1990年修改的干净空气的决议。硬件评价因素已经记载到购买者的技术说明书中，该说明书是最初的文件以保证供应商品都能满足一个最低标准。技术说明书一般包括有载重量和无载重量损失的公式、价格、噪音水平和支付日期。在设施期间的技术帮助、担保帮助和担保范围则是而外的硬件的评价因素。软件因素没有一个精确的货币价值，但在供应商的标准中也是一个很重要的比较因素。以下的列表列出了一些购买者在决定购买变压器时应该考虑的软件因素。因为它们没有直接标明价格，指定一个固

44、定的价格或是这些因素在标价中的比重对比较供应商的标价来说是很有价值的。一份良好的规范说明将所有潜在的供应商都放在了平等的位置上。应该会影响供应商的选择的软件因素设计的广泛选择;计算机援助的设计过程;R&D在产品改进中的指示;通过工业组参加长期的R&D工程;组合设备的干净工作时间;可以利用和可以替代部分;广泛的领域服务范围;帮助或协助说明;与用户的不断沟通;Tony Hartfield, ABB T&D电力公司, 电力变压器部门, 圣路易斯 , 密苏里认为在一个标准的标价被争论之前与可能的供应商来更新详细的技术规格是很重要的：“我们试图解决一些诸如内容丰富、持久耐用、胜任的的暧昧术语，并且用一些

45、可以清楚限定且应该提供的功能要求来代替它们。”“很多时候，往规范里加入一些词条来避免已经出现的问题再次发生。这样可能产生相反的结果，尤其是当今技术进步到产生问题的渊泉已经消失了。”重要的善行服勤中的记录配电变压器是在竞争激烈的情况下大批量的购买的，这时候很小幅度的单一价格变化都可以影响供应商的选择。因此，引导购买政策的最好的程序是基于职业性的单元统计记录。一个有关系统的故障分析程序的例子是由Wisconsin公共服务公司提出的。（电气世界，1991年9月，73页）。从80年代中期电力公司购买的所有变压器和所有变压器的故障记录都进入了计算机化的记录保存系统中。故障率和等价成本在4年一次的滚动信息窗中为每一个制造商都计算了出来。依照资深的标准高级工程师麦可，系统实际上降低了故障率，提高了与变压器买主的沟通，降低了成本和损耗。系统甚至帮助一些制造商来降低故障率。乔治电力公司的卖主估计这个程序已经实施存在了5年。该程序把供应商和产品分开来看，根据预先存在的标准来分别评价。权衡每一个标准下的分数，所有计算得来的数字相乘，可用于最初的标价。David