外文翻譯---發(fā)電機(jī)和變壓器

1、<p><b>　　附錄一</b></p><p><b>　　英文原文</b></p><p>　　Generator And Transformer</p><p>　　The turbine turns the rotor of the electric generator in whose stator

2、are embedded three windings. In the process mechanical power from the turbine drive is converted to three phase alternating current at voltages in the range of 11kV to 30kV line to line at a frequency of 60 Hz in the Uni

3、ted States. The voltage is usually stepped up by transmission to remote load centers.</p><p>　　A generator (also called an alternator or synchronous generator)is shown in longitudinal cross section; the tran

4、sverse across section is approximately round. The roctoe is called round or cylindrical or smooth. We note that steam-driven turbine-generators are usually two-pole or four-pole, turning at 3600 rpm or 1800 rmp, espectiv

5、ely, corresponding to 60Hz.The high speeds are needed to achieve high steam turbine efficiencies. At these rotation rates, high centrifugal forces limit rotor diameters</p><p>　　The average power ratings of

6、the turbine-generator units we have been describing have been increasing,scince1960s, from about 300MW to about 600MW，with maximum sizes up to about 1300MW.Inceased ratings are accompained by increased rotor and stator s

7、ize, and with rotor diameters limited by centrifugal forces, the rotor lengths have been increasing. Thus in the larger sizes, the rotor lengths may be five to six times the diameters. These slender rotors resonate at cr

8、itical speeds below their rated</p><p>　　A Transformer is a device that changes ac electric energy at one voltage level into ac electric energy at another voltage level through the action of a magnetic field

9、. It consists of two or more coils of wire wrapped around a common ferro magnetic core. These coils are not directly connected. The only connection between the coils is the common magnetic flux present within the core.&l

10、t;/p><p>　　One of the transformer windings is connected to a source of ac electric power, and the second(and perhaps third)transformer winding supplies electric power to load. The transformer winding connected

11、to the power source is called the primary winding or input winding, and the winding connected to the power source is called the primary winding or output winding. If there is a third winding on the transformer, it is cal

12、led the tertiary winding.</p><p>　　Power transformer is constructed on one of two types of cores. One type of construction consists of a simple rectangular laminated piece of steel with the transformer windi

13、ngs wrapped around two sides of the rectangle. This type of construction is known as core form. The other type consists of a three-legged laminated core with the windings wrapped around the center leg. This type of const

14、ruction is known as shell form. In either case, the core is constructed of thin laminations electrically iso</p><p>　　The primary and secondary windings in a physical transformer are wrapped one on top of th

15、e other with low-voltage winding innermost. Such an arrangement serves two purpose: (1)It simplifies the problem of insulating the high-voltage winding from the core. (2)It results in much less leakAge flux than would be

16、 the two windings were separated by a distance on the core.</p><p>　　Power transformers are given a variety of different names, depending on there use in power systems. A transformer connected to the output

17、of a generator and used to step its voltage to transmission levels is sometimes called a unit transformer. The transformer at the other end of the transmission line, which steps the voltage down from transmission levels,

18、 is called a substation transformer. Finally, the transformer that takes his distribution levels, is called a distribution transformer. All th</p><p>　　In addition to the various power transformer, two-speci

19、al purpose transformers are used with electric machinery and power systems. The first of these special transformers is a device specially designed to sample a high voltage and produce a low secondary voltage directly pro

20、portional to it. Such a transformer is called a potential transformer. A power transformer also produces a secondary voltage directly proportional to its primary voltage; the different between a potential transformer and

21、 a po</p><p>　　Transformers 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 o

22、ne coil; most have two although they may have many more.</p><p>　　The usual purpose of transformers is to change the level of voltage. But sometimes they are used to isolate a load from the power source.<

23、/p><p>　　Standard power transformers have two oils. These coils are labeled PRIMARY and SECONDARY. The primary coil is the one connected to the source. The secondary is the one connected to the load .There is n

24、o electrical connection between the primary and secondary. The secondary gets its voltage by induction.</p><p>　　The only place where you will see a STEP-UP transformer is at the generating station. Typicall

25、y, electricity is generated at 13,800 volts. It is stepped up to 345,000 volts for transmission. The next stop is the substation where it is stepped down to distribution levels, around 15,000 volts. Large substation tran

26、sformers have cooling fins to keep them from overheating. Other transformers are located near points where the electric power is used.</p><p>　　The coils of transformer are electrically are electrically insu

27、lated from each other. There is a 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 curr

28、ent in both primary and secondary.</p><p>　　There are two main designs for cores:</p><p>　　1.The CORE type has the core inside the windings.</p><p>　　2.The SHELL type has the core o

29、utside.</p><p>　　Smaller power transformers are usually of the core type. The very large transformers are of the shell type. There is no different in their operation, however.</p><p>　　Coils are

30、 wound with copper wire. The resistance is kept as low as possible to keep losses low.</p><p>　　Transformers are very efficient. The losses are often less than 3 percent. This allows us to assume that they a

31、re perfect in many computations.</p><p>　　Perfect means that the wire has no resistance. It also means that there are no power losses in the core.</p><p>　　Further, we assume that there is no fl

32、ux leakAge. That is, all of the magnetic flux links all of the turns on each coil.</p><p>　　To get an idea of just how small the losses are ,we can take a look at the EXCITATION CURRENT. Assume that nothing

33、is connected to the secondary. If you apply rated voltage to the primary, a small current flows. Typically, this excitation current is less than 3 percent of rated current supplies the power lost in the core. Core losses

34、 are due to EDDY CURRENTS and HYSTERESIS.</p><p>　　Eddy currents circulating in the core result from induction .The core is, after all, a conductor within a changing magnetic field.</p><p>　　Hys

35、teresis 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.</p><p>　　The other part of the excitation c

36、urrent magnetizes the core. It is this magnetizing current that supplies the “shuttle power”. Shuttle power is power stored in the magnetic field and returned to the source twice each cycle. Magnetizing current is quadra

37、ture with the applied voltage.</p><p>　　Excitation current is made up of two parts. One part is in phase with the voltage. </p><p>　　The losses that occur in real transformers have to be account

38、ed for in any accurate model of transformer behavior. The major items to be considered in the construction shuttle such a model are.</p><p>　　(i)Copper losses. Copper losses are the resistive heating losses

39、in the primary and secondary windings of the transformer. They are proportional to there turn square of the current in the windings.</p><p>　　(ii)Eddy current losses. Eddyysteresis loss is current losses are

40、 resistive heating losses in the core of the transformer.</p><p>　　(iii)Hysteresis losses. These losses are associated with the rearrangement of the magnetic domains in the core during each half-cycle.</p

41、><p>　　(iv)LeakAge flux. The fluxes which escape the core and pass through only one of the transformer windings are leakAge fluxes. These escaped fluxes produce a self-inductance in the primary and secondary co

42、ils, and the effects of this inductance must be accounted for</p><p><b>　　英文譯文</b></p><p><b>　　發(fā)電機(jī)和變壓器</b></p><p>　　汽輪機(jī)驅(qū)動(dòng)發(fā)電機(jī)的轉(zhuǎn)子，通過(guò)嵌在其定子槽內(nèi)的三相繞組將輸入的機(jī)械能轉(zhuǎn)變?yōu)槿嘟涣麟?/p>

43、能。其額定電壓在美國(guó)從11kV到30kV不等，頻率為60 Hz。為了提高遠(yuǎn)距離輸電的效率，要用變壓器將電壓升高。</p><p>　　發(fā)電機(jī)（也一般稱(chēng)交流發(fā)電機(jī)或同步發(fā)電機(jī)）的縱向剖面圖，其橫斷面近似圓形，因此轉(zhuǎn)子也稱(chēng)為圓筒轉(zhuǎn)子。我們注意到汽輪發(fā)電機(jī)一般是兩極或四極的，轉(zhuǎn)速為3600r/min或1800r/min，分別與60Hz的頻率相對(duì)應(yīng)。為了獲得汽輪機(jī)的高效率，需要有很高的轉(zhuǎn)速，而由此產(chǎn)生的較高離心力又限制了

44、轉(zhuǎn)子的直徑，兩極的轉(zhuǎn)子直徑極限大約為3.5英尺，四極的大約為7英尺。</p><p>　　上述這種汽輪發(fā)電機(jī)組的平均額定自然功率自1960年以來(lái)一直在提高，從大約300MW到600MW，最大達(dá)1300MW，額定功率的增加要求轉(zhuǎn)子和定子的尺寸增大，而由于轉(zhuǎn)子 直徑受離心力的限制，其長(zhǎng)度必須增加，可能增至其直徑的5倍到6倍。這些細(xì)長(zhǎng)的轉(zhuǎn)子在低于其額定轉(zhuǎn)速的某個(gè)臨界速度下會(huì)發(fā)生諧振，因此操作中應(yīng)避免持續(xù)運(yùn)行在這種轉(zhuǎn)速下

45、。</p><p>　　變壓器是通過(guò)磁場(chǎng)作用將交流電從某一電壓等級(jí)轉(zhuǎn)換至另一電壓等級(jí)的設(shè)備。它由兩個(gè)或多個(gè)繞在鐵體上的繞組構(gòu)成。通常，繞組之間不直接相連，他們是通過(guò)鐵芯內(nèi)部的主磁通相連接的。</p><p>　　變壓器的一個(gè)繞組與交流電源連接，第二個(gè)繞組（也許第三個(gè)繞組）為負(fù)載提供電功率。與電源連接的繞組稱(chēng)為一次繞組或輸入繞組。與負(fù)載連接的繞組稱(chēng)為二次繞組或輸出繞組。如果有第三個(gè)繞組，稱(chēng)之

46、為第三繞組。</p><p>　　變壓器的鐵芯分為兩類(lèi)。一類(lèi)是由繞組纏繞在一個(gè)簡(jiǎn)單的矩形鋼片疊成的鐵芯兩邊而構(gòu)成。此類(lèi)結(jié)構(gòu)的繞組稱(chēng)為鐵芯式結(jié)構(gòu)。另一類(lèi)是由三個(gè)分支的鋼片疊成，繞組繞在中間的一個(gè)分支上。此類(lèi)結(jié)構(gòu)稱(chēng)為框式結(jié)構(gòu)。鐵芯不論是芯式還是框式，都是由薄薄的鐵芯片做成的。鐵心片之間相互絕緣，以最大限度的降低渦流。</p><p>　　實(shí)際的變壓器中，一次繞組和二次繞組一個(gè)在另一個(gè)的外面，低

47、壓繞組在最里面。此類(lèi)結(jié)構(gòu)安排有兩個(gè)目的：（1）使高壓繞組與鐵芯之間相互絕緣；（2）使漏磁通較二個(gè)繞組相互隔開(kāi)時(shí)少的多。</p><p>　　在電力系統(tǒng)中，根據(jù)不同的用途，電力變壓器有許多種不同的名稱(chēng)。與發(fā)電機(jī)連接并將其電壓提高到電網(wǎng)電壓的變壓器被稱(chēng)為升壓變壓器。在輸電線另一端，將電網(wǎng)電壓降至配電電壓的變壓器稱(chēng)為降壓變壓器。最后，把電壓降低到能實(shí)際應(yīng)用量級(jí)的變壓器稱(chēng)為配電變壓器。以上變壓器的結(jié)構(gòu)基本相同，唯一的區(qū)別

48、在于各自的實(shí)際用途不同。</p><p>　　除了上述多種變壓器之外，在電機(jī)與電力系統(tǒng)中還使用兩種特殊用途的變壓器。第一種專(zhuān)門(mén)設(shè)計(jì)的變壓器是用來(lái)采樣電壓，并產(chǎn)生一個(gè)低的二次電壓，該電壓與所采樣的電壓成正比。此類(lèi)變壓器稱(chēng)為電壓互感器。功率變壓器中產(chǎn)生的二次側(cè)的電壓也與一次側(cè)的電壓成正比。但電壓互感器與電力變壓器的不同在于電壓互感器設(shè)計(jì)為僅處理較小的電流。第二種專(zhuān)門(mén)設(shè)計(jì)的變壓器設(shè)計(jì)成為用來(lái)提供比一次側(cè)的電流要小的多的

49、二次側(cè)電流，且使二次側(cè)的電流與一次側(cè)的電流成正比。此類(lèi)裝置稱(chēng)為電流互感器。</p><p>　　變壓器的大小不一，有的變壓器像房子一樣大，而電子變壓器可能小如糖塊。所有的變壓器至少有一只線圈，大多數(shù)變壓器具有兩個(gè)或兩個(gè)以上的線圈。</p><p>　　通常使用變壓器的目的是改變電壓等級(jí)，但有時(shí)也用于隔離電源和負(fù)荷。 </p><p>　　標(biāo)準(zhǔn)電力變壓器有兩只線圈，這

50、些線圈標(biāo)記為一次繞組和二次繞組，一次繞組連接電源，二次繞組連接負(fù)荷，在一次繞組和二次繞組之間沒(méi)有電的連接，二次繞組通過(guò)感應(yīng)獲得電源。</p><p>　　大概只有發(fā)電廠才能見(jiàn)到升壓變壓器。典型的發(fā)電機(jī)出口電壓為13800V，升壓至35000V用來(lái)傳輸。下一站是變電所，把電壓降到配電電壓等級(jí)，約15000V。大型的變電所變壓器具有冷卻葉片，以防止變壓器過(guò)熱，有的變壓器安裝的位置靠近用戶。</p>&l

51、t;p>　　變壓器的線圈之間是絕緣的，但存在磁聯(lián)系。兩只線圈繞在同一個(gè)鐵芯上。一次繞組電流使鐵芯磁化，并在鐵芯中產(chǎn)生磁場(chǎng)。鐵芯磁場(chǎng)影響一次和二次繞組的電流。</p><p>　　鐵芯主要有兩種型式：</p><p>　　1.心型。鐵芯在線圈內(nèi)部。</p><p>　　2.殼型。鐵芯在線圈外部。</p><p>　　小型電力變壓器通常為心

52、型。特大型變壓器為殼型，但是在運(yùn)行時(shí)二者并無(wú)區(qū)別。</p><p>　　線圈用銅線繞成。電阻應(yīng)盡量小，從而保持低損耗。</p><p>　　變壓器效率很高，損耗統(tǒng)常低于3%,因此這使我們假定它在計(jì)算時(shí)是無(wú)損耗的。無(wú)損耗意味著線圈沒(méi)有電阻，并且鐵芯中沒(méi)有能量損耗。進(jìn)一步可以假定沒(méi)有漏磁，即所有的磁力線穿過(guò)線圈的每一匝。</p><p>　　欲知損耗的大小，可以看一下勵(lì)

53、磁電流。假定二次繞組空載，在一次繞組施加額定電壓之后會(huì)產(chǎn)生一較小的電流。典型情況是該勵(lì)磁電流小于額定電流的3%。勵(lì)磁電流由兩部分組成，一部分與電壓同相，該電流供給鐵芯中的能量損耗。鐵芯損耗的原因是渦流電流和磁滯。流電流在鐵芯中旋轉(zhuǎn)，產(chǎn)生感應(yīng)現(xiàn)象，因?yàn)殍F芯畢竟是變化磁場(chǎng)的導(dǎo)體。</p><p>　　磁滯損耗是由于用來(lái)排列鐵芯中的磁疇需要能量。這種排列調(diào)整是連續(xù)不斷的，開(kāi)始是一個(gè)方向，然后是另一個(gè)方向。另一部分勵(lì)磁電

54、流磁化鐵芯。磁化電流供給“往復(fù)能量”，往復(fù)能量就是儲(chǔ)存在磁場(chǎng)中的能量，并在每個(gè)周期內(nèi)返回電源兩次。磁化電流與所加電壓正交。</p><p>　　在任何精確的變壓器模型中，均應(yīng)考慮變壓器在工作間的實(shí)際損耗，在這些模型中，主要考慮一些內(nèi)容：</p><p>　　1）銅損：在變壓器一次繞組和二次繞組上，由電阻產(chǎn)生的熱損耗稱(chēng)為銅損。銅損與繞組內(nèi)通過(guò)電流的平方成正比。</p><

55、p>　　2）渦流損耗：渦流損耗是在變壓器的鐵芯中由于電阻而產(chǎn)生的熱損耗。</p><p>　　3）磁滯損耗：這些損耗是鐵芯中的磁疇在每半周期內(nèi)重新排列而造成的損耗。</p><p>　　4）漏磁通：漏磁通指從鐵芯中泄露出來(lái)以至于僅通過(guò)變壓器的一個(gè)繞組的磁通。這些漏磁會(huì)在一次繞組和二次繞組中產(chǎn)生自感，因此必須考慮自感所帶來(lái)的影響。在變壓器實(shí)際應(yīng)用中，將上述損耗全部考慮在內(nèi)，構(gòu)成一個(gè)等效