直流發(fā)電機(jī)畢業(yè)設(shè)計(jì)外文翻譯

1、<p>　　附錄1 外文資料翻譯</p><p><b>　　A1.1 譯文</b></p><p><b>　　直流發(fā)電機(jī)</b></p><p><b>　　1.介紹</b></p><p>　　對于所有實(shí)際目的來說，直流發(fā)電機(jī)僅用于特殊場合和地方性發(fā)電廠。這個(gè)局

2、限性是由于換向器要把發(fā)電機(jī)內(nèi)部的電壓整流為直流電壓，因此使大規(guī)模直流發(fā)電不能實(shí)行。</p><p>　　結(jié)果，所有大規(guī)模生產(chǎn)的電能都以三相交流電的形式生產(chǎn)和分配。今天固態(tài)轉(zhuǎn)換器的應(yīng)用使交流變直流成為可能。而且，直流發(fā)電機(jī)的操作特性一直重要，因?yàn)榇蟛糠值睦碚撃鼙粦?yīng)用到所有其它機(jī)器上。

3、 </p><p><b>　　2.勵(lì)磁繞組連接</b></p><p>　　對于一個(gè)有四個(gè)電極的機(jī)器其電刷和勵(lì)磁繞組的一般布置如圖1所示。四個(gè)電刷安在換向器上，正極電刷和A1端子相連，負(fù)極電刷和A2端子相連。正如在草圖中所示，電刷被放置在電極下接近中間的位置，它們與線圈相接觸，這些線圈產(chǎn)生很少或不產(chǎn)生電動(dòng)勢，因?yàn)樗鼈冞叡话苍陔姌O之間。</p&g

4、t;<p>　　圖1 四極發(fā)電機(jī)模型</p><p>　　四個(gè)勵(lì)磁磁極通常串聯(lián)在一起，并且它們的末端與標(biāo)注F1和F2的端子相連。它們這樣連接是為了交替產(chǎn)生N,S極。</p><p>　　直流發(fā)電機(jī)的類型以勵(lì)磁繞組提供的方式來劃分。一般來說，用來連接勵(lì)磁繞組和電樞繞組的方式可歸結(jié)為以下幾組（看圖2）：</p><p>　　圖2 直流發(fā)電機(jī)勵(lì)磁連接：(a

5、)它勵(lì)發(fā)電機(jī)；(b)自勵(lì)，自并勵(lì)；(c)串勵(lì)發(fā)電機(jī)；(d)復(fù)勵(lì)發(fā)電機(jī)，短并勵(lì)連接；(e)復(fù)勵(lì)發(fā)電機(jī)，長并勵(lì)連接。</p><p>　　它勵(lì)發(fā)電機(jī)，勵(lì)磁繞組被連接到一個(gè)獨(dú)立的直流供電源上。</p><p>　　自勵(lì)發(fā)電機(jī)，它們可以進(jìn)一步劃分為：</p><p>　　并勵(lì)發(fā)電機(jī)，勵(lì)磁繞組和轉(zhuǎn)子端部相連。</p><p>　　串勵(lì)發(fā)電機(jī)，勵(lì)磁繞組以

6、串聯(lián)方式和轉(zhuǎn)子繞組相連。</p><p>　　復(fù)勵(lì)發(fā)電機(jī)，勵(lì)磁由一個(gè)并聯(lián)和串聯(lián)的復(fù)合繞組提供。</p><p>　　并聯(lián)繞組包括很多匝相對較細(xì)的細(xì)線，它們只能承載一個(gè)較小的電流，僅為額定電流的很小一個(gè)百分比。另一方面，串聯(lián)繞組有很少匝粗線，因?yàn)樗娃D(zhuǎn)子串聯(lián)，因而承載較重的電流。</p><p>　　在討論直流發(fā)電機(jī)端部特性之前，讓我們測試一下發(fā)電機(jī)在空載時(shí)的電壓和勵(lì)

7、磁電流之間的關(guān)系。發(fā)電機(jī)電動(dòng)勢和每個(gè)電極的磁通及發(fā)電機(jī)給定的轉(zhuǎn)速成正比，即，EG=knφ,通過控制讓轉(zhuǎn)速為定值，可以顯示出電勢EG直接依賴于磁通，在實(shí)際的發(fā)電機(jī)上測試這種依賴關(guān)系并不是非常實(shí)際的，因?yàn)樗獱可娴酱磐ǖ臏y量。磁通由勵(lì)磁線圈的安培匝數(shù)產(chǎn)生；磁通必需依賴于勵(lì)磁電流的大小，因?yàn)閯?lì)磁線圈的匝數(shù)是恒定的。這種關(guān)系并不是線性的，因?yàn)樵趧?lì)磁電流達(dá)到某一個(gè)值后將出現(xiàn)磁飽和，EG對勵(lì)磁電流If的變化關(guān)系可以磁化曲線或開路特性曲線來表示，對于

8、這臺給定以恒速運(yùn)轉(zhuǎn)的發(fā)電機(jī)，沒有帶負(fù)載電流，并且它的勵(lì)磁是它勵(lì)方式。</p><p>　　If從0逐漸增大到一個(gè)適宜的值，使發(fā)電機(jī)機(jī)端電壓達(dá)到額定電壓以上，并測量相對應(yīng)If的每個(gè)機(jī)端電壓EG的值，產(chǎn)生的曲線入圖3所示，當(dāng)If=0時(shí)，即勵(lì)磁回路為開路，由于剩磁，測量到一個(gè)很小的電壓Er，隨著勵(lì)磁電流的增大，產(chǎn)生的電動(dòng)勢線性地增大到磁化曲線的拐點(diǎn)處，過了這個(gè)點(diǎn)以后，增大勵(lì)磁電流逐漸引起磁路飽和。</p>

9、<p>　　圖3 它勵(lì)支直流發(fā)電機(jī)的磁化曲線或開路特性曲線</p><p>　　這意味著使電壓達(dá)到一定值時(shí)需要一個(gè)更大的勵(lì)磁電流。</p><p>　　因?yàn)楫a(chǎn)生的電壓EG也直接與轉(zhuǎn)速成比例，因此一旦這條曲線確定，對于任何其它速度，這條磁化曲線能被描出來，這僅僅要求依照</p><p>　　EG‘=EG*n’/n</p><p>　

10、　在這條曲線上所有點(diǎn)進(jìn)行調(diào)整。</p><p><b>　　3.電壓調(diào)整</b></p><p>　　讓我們進(jìn)一步考慮在發(fā)電機(jī)上增加一個(gè)負(fù)載的情況。因?yàn)殡姌欣@組上有電阻，所以機(jī)端電壓將要下降，除非采取一些措施保持它恒定，顯示機(jī)端電壓隨負(fù)載電流變化關(guān)系的曲線被叫做負(fù)載特性曲線或外特性曲線。</p><p>　　圖4 （a）直流它勵(lì)發(fā)電機(jī)負(fù)載特性；

11、(b)電路圖</p><p>　　圖4顯示了它勵(lì)發(fā)電機(jī)的外特性，機(jī)端電壓下降主要是因?yàn)殡姌须娮鑂A,即Vt=EG-IARA</p><p>　　此處Vt是機(jī)端電壓，IA是發(fā)電機(jī)帶負(fù)載時(shí)的電樞電流（或負(fù)載電流）。</p><p>　　另一個(gè)導(dǎo)致機(jī)端電壓下降的因素是由于電樞反應(yīng)而導(dǎo)致磁通的減少。電樞電流建立一個(gè)磁動(dòng)勢，這個(gè)磁動(dòng)勢使主磁通發(fā)生畸變，導(dǎo)致弱磁效應(yīng)，這種情況尤

12、其在無附加磁極機(jī)器上表現(xiàn)更為突出，這種效應(yīng)叫做電樞反應(yīng)。正如圖4所示，因?yàn)殍F心的非線形，機(jī)端電壓對于負(fù)載電流并沒有成線形下降。由于電樞反應(yīng)依賴于電樞電流，使得曲線呈下傾特性。</p><p><b>　　四.并勵(lì)或自并勵(lì)</b></p><p>　　并勵(lì)發(fā)電機(jī)的并勵(lì)勵(lì)磁繞組電樞繞組平行連接，以便機(jī)器本身提供它的自己的勵(lì)磁，正如圖5所示。</p><

13、p>　　電壓的建立正如所說的，在勵(lì)磁磁極中要有剩磁。通常，假如發(fā)電機(jī)以前已經(jīng)用過，將會有剩磁存在。我們已經(jīng)在第三部分中看到假如勵(lì)磁沒連上的話如果發(fā)電機(jī)已經(jīng)以某速度運(yùn)轉(zhuǎn)，因?yàn)橛惺４艑⒁行〉碾妷篍r產(chǎn)生，這個(gè)小的電壓將提供給并勵(lì)繞組并驅(qū)動(dòng)一個(gè)小的電流從勵(lì)磁回路中流過，假如在并勵(lì)繞組中的這個(gè)小的電流的方向正好使剩磁減弱，則這個(gè)電壓將接近于零，機(jī)端電壓不能建立。這種情況下這個(gè)弱化主磁極的磁通與剩磁抵消。</p><p

14、>　　圖5 并勵(lì)發(fā)電機(jī)：（a）電路；(b)負(fù)載特性</p><p>　　假如關(guān)系是這樣：弱化主磁極的磁通助增了剩磁通，導(dǎo)致電壓變的更大，這反過來意味著更大的電壓提供給了主勵(lì)磁，機(jī)端電壓快速增大一個(gè)常值，這個(gè)建立的過程易看成是漸增的，然后更大的增大了勵(lì)磁電流，它反過來又增大了電壓，等。這個(gè)過程終止于一個(gè)有限的電壓值的原因是磁路的非線性。</p><p>　　這個(gè)電路僅有直流電流，以致勵(lì)

15、磁電流僅依賴于勵(lì)磁回路的電阻Rf,這可能由勵(lì)磁繞組電阻加上與它相串聯(lián)的可變電阻Rin組成。對于一給定值的勵(lì)磁回路電阻Rf ，按照歐姆定律，勵(lì)磁電流依賴于所產(chǎn)生的電壓。</p><p>　　應(yīng)該是明顯的，在一臺新機(jī)器上或一臺閑置了很常時(shí)間已經(jīng)失去剩磁的機(jī)器上，必須要建立磁場，通常做法是通過連接勵(lì)磁繞組到一獨(dú)立直流電源上幾秒鐘，這個(gè)過程正是快速建立勵(lì)磁。</p><p>　　總之，阻止電壓建立

16、有四種條件，發(fā)電機(jī)電壓極性取決于轉(zhuǎn)動(dòng)的方向，假如一臺發(fā)電機(jī)在其它條件都滿的情況下不能建立電壓，那肯定是電刷的極性反了，可以通過顛倒轉(zhuǎn)動(dòng)方向來解決 ，顛倒方向后關(guān)于剩磁通的主磁極性也將顛倒，假如現(xiàn)在電壓還不能建立，它意味著主勵(lì)磁和剩磁是對立的。</p><p><b>　　串勵(lì)發(fā)電機(jī)</b></p><p>　　正如前面提到的，串勵(lì)發(fā)電機(jī)的勵(lì)磁繞組和電樞繞組串聯(lián)因?yàn)樗?/p>

17、載負(fù)荷電流，因此勵(lì)磁線圈僅由幾匝細(xì)導(dǎo)線?？蛰d時(shí)，僅有剩磁，機(jī)端電壓小，當(dāng)加上負(fù)載時(shí)，磁通增加，機(jī)端電壓也增加，圖7顯示了串勵(lì)發(fā)電機(jī)在某轉(zhuǎn)速運(yùn)轉(zhuǎn)時(shí)的負(fù)載特性，虛線指示同臺機(jī)器電樞開路且它勵(lì)情況下所產(chǎn)生的電動(dòng)勢，這兩條曲線的差值簡直就是在串勵(lì)繞組和電樞繞組上的IR的壓降，例如，</p><p>　　Vt=EG-IA(RA+RS)</p><p>　　此處，RS是串勵(lì)繞組電阻</p>

18、<p>　　圖7 串勵(lì)發(fā)電機(jī)：（a）電路圖；（b）負(fù)載特性</p><p><b>　　復(fù)勵(lì)發(fā)電機(jī)</b></p><p>　　復(fù)勵(lì)發(fā)電機(jī)有一個(gè)并勵(lì)和一個(gè)串勵(lì)勵(lì)磁繞組，后者在并勵(lì)繞組的頂部，圖8顯示了這個(gè)電路圖，這兩個(gè)繞組通常這樣連接是為了使它們的安培匝數(shù)在相同方向，正因?yàn)槿绱?，這種發(fā)電機(jī)被稱作積復(fù)勵(lì)。</p><p>　　圖8的

19、并聯(lián)連接被稱作長復(fù)勵(lì)。假如并勵(lì)繞組直接和電樞端部連接在一塊，這種連接被稱作短復(fù)勵(lì)，實(shí)際中這種連接很少應(yīng)用，因?yàn)楹蜐M負(fù)荷電流相比，并勵(lì)繞組承載的電流小，此外串勵(lì)繞組匝數(shù)少，這意味著它的電阻也小，在滿負(fù)荷時(shí)在它上面所對應(yīng)的電壓降是最小的。</p><p>　　圖9曲線僅僅反映了并勵(lì)繞組外特性，正如所示隨著一個(gè)小串勵(lì)繞組的增加，機(jī)端壓降隨負(fù)荷增加而減小，這樣的發(fā)電機(jī)被稱作欠復(fù)勵(lì)，通過增加串勵(lì)匝數(shù)，空載和滿載時(shí)機(jī)端電壓能

20、夠相等，這種發(fā)電機(jī)被稱作平復(fù)勵(lì)。假如串勵(lì)匝數(shù)比需要的多些以補(bǔ)償電壓降，這種發(fā)電機(jī)被稱作過復(fù)勵(lì)，在這種情況下，滿載電壓比空載時(shí)還高。</p><p>　　圖8復(fù)勵(lì)發(fā)電機(jī) 圖9復(fù)勵(lì)發(fā)電機(jī)外特性與并勵(lì)發(fā)電機(jī)外特性比較</p><p>　　過復(fù)勵(lì)可能被用于負(fù)荷與發(fā)電機(jī)存在一定距離的場合，在饋電線上的電壓降隨著負(fù)載增加而得到補(bǔ)償。顛倒和并勵(lì)相對應(yīng)的串勵(lì)繞組的極性時(shí)，勵(lì)磁

21、將彼此抵消，且隨著負(fù)荷電流的增加而尤為突出，這樣的發(fā)電機(jī)被稱作差復(fù)勵(lì)，它被用于負(fù)荷可能發(fā)生或接近短路的場合，例如，饋電線可能斷線或短接發(fā)電機(jī)，不過短路電流仍被限制在一個(gè)安全的值，這種類型的發(fā)電機(jī)的外特性也顯示在圖9中。因?yàn)閺?fù)勵(lì)發(fā)電機(jī)的外特性能被設(shè)計(jì)的有很廣的變化范圍，故這種發(fā)電機(jī)比其他類型的有更廣的用途。</p><p>　　正如插圖中所示，在復(fù)勵(lì)合適的角度下，滿載時(shí)機(jī)端電壓能被保持在空載時(shí)的值上。電壓控制的其他

22、方法是可變電阻的使用，。例如，裝在勵(lì)磁回路上。不過，隨著負(fù)荷的變化，要求恒定調(diào)節(jié)可變電阻來保持電壓。</p><p>　　一個(gè)更有用的現(xiàn)在普遍使用的東西是用一臺發(fā)電機(jī)電壓自動(dòng)調(diào)節(jié)裝置，在本質(zhì)上，電壓調(diào)節(jié)器是一個(gè)反饋控制系統(tǒng)，發(fā)電機(jī)輸出的電壓能夠被感知并于一個(gè)固定的參考電壓相比較，任何輸出電壓只要偏離參考電壓，就將發(fā)出一誤差信號，并送入功率放大器，而這個(gè)功率放大器提供勵(lì)磁電流，假如誤差信號為正，例如，輸出電壓大于設(shè)

23、定電壓，則功率放大器蔣減小它的電流驅(qū)動(dòng)，如此，直到偏差信號減小為零。</p><p>　　譯自<< College English Reading For Students Of Electric Reading>></p><p><b>　　A1.2 原文</b></p><p>　　DC GENENRATORS&l

24、t;/p><p>　　1. INTRODUCTION</p><p>　　For all practical purposes, the direct-current generator is only used for special applications and local dc power generation. This limitation is due to the commu

25、tator required to rectify the internal generated ac voltage, thereby making largescale dc power generators not feasible.</p><p>　　Consequently, all electrical energy produced commercially is generated and di

26、stributed in the form of three-phase ac power. The use of solid state converters nowadays makes conversion to dc economical. However, the operating characteristics of dc generators are still important, because most conce

27、pts can be applied to all other machines.</p><p>　　2. FIELD WINDING CONNECTIONS</p><p>　　The general arrangement of brushes and field winding for a four-pole machine is as shown in Fig.1. The fo

28、ur brushes ride on the commutator. The positive brusher are connected to terminal A1 while the negative brushes are connected to terminal A2 of the machine. As indicated in the sketch, the brushes are positioned approxim

29、ately midway under the poles. They make contact with coils that have little or no EMF induced in them, since their sides are situated between poles.</p><p>　　Figure 1 Sketch of four-pole dc matchine</p>

30、;<p>　　The four excitation or field poles are usually joined in series and their ends brought out to terminals marked F1 and F2. They are connected such that they produce north and south poles alternately.</p&g

31、t;<p>　　The type of dc generator is characterized by the manner in which the field excitation is provided. In general, the method employed to connect the field and armature windings falls into the following groups

32、 (see Fig.2):</p><p>　　Figure 2 Field connections for dc generators:(a)separately excited generator;(b)self-excited,shunt generator;(c)series generator;(d)compound generator;short-shunt connection;(e)compoun

33、d generator,long-shunt connection.</p><p>　　The shunt field contains many turns of relatively fine wire and carries a comparatively small current, only a few percent of rated current. The series field windin

34、g, on the other hand, has few turns of heavy wire since it is in series with the armature and therefore carries the load current.</p><p>　　Before discussing the dc generator terminal characteristics, let us

35、examine the relationship between the generated voltage and excitation current of a generator on no load. The generated EMF is proportional to both the flux per pole and the speed at which the generator is driven, EG=kn.

36、By holding the speed constant it can be shown the EG depends directly on the flux. To test this dependency on actual generators is not very practical, as it involves a magnetic flux measurement. The flux is produ</p&g

37、t;<p>　　The value of EG appearing at the machine terminals is measured as If is progressively increased from zero to a value well above rated voltage of that machine. The resulting curve is shown is Fig.3. When Ij

38、=0, that is, with the field circuit open circuited, a small voltage Et is measured, due to residual magnetism. As the field current increases, the generated EMF increases linearly up to the knee of the magnetization curv

39、e. Beyond this point, increasing the field current still further causes sat</p><p>　　Figure 3 Magnetization curve or open-circuit characteristic of a separately excited dc machine</p><p>　　The m

40、eans that a larger increase in field current is required to produce a given increase in voltage.</p><p>　　Since the generated voltage EG is also directly proportional to the speed, a magnetization curve can

41、be drawn for any other speed once the curve is determined. This merely requires an adjustment of all points on the curve according to</p><p>　　where the quantities values at the various speeds.</p>&l

42、t;p>　　3. VOLTAGE REGULATION</p><p>　　Let us next consider adding a load on generator. The terminal voltage will then decrease (because the armature winding ha resistance) unless some provision is made to

43、keep it constant. A curve that shows the value of terminal voltage for various load currents is called the load or characteristic of the generator.</p><p>　　Fig.4 shows the external characteristic of a separ

44、ately excited generator. The decrease in the terminal voltage is due mainly to the armature circuit resistance RA. In general, </p><p>　　where Vt is the terminal voltage and IA is the armature current (or lo

45、ad current IL) supplied by the generator to the load.</p><p>　　Another factor that contributes to the decrease in terminal voltage is the decrease in flux due to armature reaction. The armature current estab

46、lished an MMF that distorts the main flux, resulting in a weakened flux, especially in noninterpole machines. This effect is called armature reaction. As Fig.4 shows, the terminal voltage versus load current curve does n

47、ot drop off linearly since the iron behaves nonlinear. Because armature reaction depends on the armature current it gives the curve its </p><p>　　4. SHUNT OR SELF-EXCIITED GENRATORS</p><p>　　A s

48、hunt generator has its shunt field winding connected in parallel with the armature so that the machine provides its own excitation, as indicated in Fig.5. The question arises whether the machine will generate a voltage a

49、nd what determines the voltage.</p><p>　　For voltage to “build up” as it is called, there must be some remanent magnetism in the field poles. Ordinarily, if the generator has been used previously, there will

50、 be some remanent magnetism. We have seen in Section 3 that if the field would be disconnected, there will be small voltage Ef generated due to this remanent magnetism, provided that the generator is driven at some speed

51、. Connecting the field for self-excitation, this small voltage will be applied to the shunts field and drive a sma</p><p>　　Figure 5 Shunt generator:(a)circuit;(b)load characteristic</p><p>　　If

52、 the connection is such that the weak main pole flux aids the residual flux, the induced voltage increases rapidly to a large, constant value. The build-up process is readily seen to be cumulanve. That is, more voltage i

53、ncreases the field current, which in turn increases the voltage, and so on. The fact that this process terminates at a finite voltage is due to the nonlinear behavior of the magnctic circuit. In steady state the generate

54、d voltage is causes a field current to flow that is just s</p><p>　　The circuit carries only dc current, so that the field current depends only on the field circuit resistance, Rf. This may consist of the fi

55、eld circuit resistance Rf, the field current depends on the generated voltage in accordance with Ohm’s law.</p><p>　　It should be evident that on a new machine or one that has lost its residual flux because

56、of a long idle period, some magnetism must be created. This is usually done by connecting the field winding only to a separate dc source for a few seconds. This procedure is generally known as flashing the field.</p&g

57、t;<p>　　Series Generators</p><p>　　As mentioned previously, the field winding of a series generator is in series with the armature. Since it carries the load current the series field winding consists

58、of only a few turns of thick wire. At no load, the generated voltage is small due to residual field flux only. When a load is added, the flux increases, and so does the generated voltage. Fig.7 shows the load characteris

59、tic of a series generator driven at a certain speed. The dashed line indicates the generated EMF of the same machin</p><p>　　where RS is the series field winding resistance.</p><p>　　Figure 7 Se

60、ries generator: (a)circuit diagram;(b)load characteristics</p><p>　　Compound Generators</p><p>　　The compound generator has both a shunt and a series field winding, the latter winding wound on t

61、op of the shunt winding. Fig.8 shows the circuit diagram. The two windings are usually connected such that their ampere-turns act in the same direction. As such the generator is said to be cumulatively compounded.</p&

62、gt;<p>　　The shunt connection illustrated in Fig.8 is called a long shunt connection. If the shunt field winding is directly connected across the armature terminals, the connection is referred to as a short shunt.

63、 In practice the connection used is of little consequence, since the shunt field winding carries a small current compared to the full-load current. Furthermore, the number of turns on the series field winding. This impli

64、es it has a low resistance value and the corresponding voltage drop across i</p><p>　　Curves in Fig.9 represents the terminal characteristic of the shunt field winding alone. By the addition of a small serie

65、s field winding the drop in terminal voltage with increased loading is reduced as indicated. Such a generator is said to be undercompounded. By increasing the number of series turns, the no-load and full-load terminal vo

66、ltage can be made equal; the generator is then said to be flatcompounded. If the number of series turns is more than necessary to compensate for the voltage dr</p><p>　　Figure 9 Terminal characteristics of c

67、ompound generators compared with that of the shunt generator</p><p>　　The overcompounded generator may be used in instances where the load is at some distance from the generator. The voltage drops in the fee

68、der lines are the compensated for with increased loading. Reversing the polarity of the series field in relation to the shunt field, the fields will oppose each other more and more as the load current increase. Such a ge

69、nerator is said to be differentially compounded. It is used in applications where feeder lines could occur approaching those of a short circuit</p><p>　　As illustrated, the full-load terminal voltage can be

70、maintained at the no-load value by the proper degree of compounding. Other methods of voltage control are the use of rheostats, for instance, in the field circuit. However, with changing loads it requires a constant adju

71、stment of the field rheostat to maintain the voltage. A more useful arrangement, which is now common practice, is to use an automatic voltage regulator with the generator. In essence, the voltage regulator is a feedback