外文翻譯--變壓器的類(lèi)型及結(jié)構(gòu)

1、<p>　　Types and Construction of Transformer</p><p>　　A Transformer is a device that changes ac electric energy at one voltage level into ac e1ectric energy at another vo1tage level through the action of

2、 a ma8netic field．It consists of two or more coil of wire wrapped around a common ferromagnetic core．These coils are (usually) not directly connected．The only connection between the coils is the common magnetic flux pres

3、ent within the core.</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 loads．The transf

4、ormer winding connected to the power source is called the primary winding or input winding，and the winding connected to the loads is called the secondary winding or output winding. If there is a third winding on the tran

5、sformer，it is called the tertiary winding．</p><p>　　Power transformer are constructed on one of two types of cores．One type of construction consists of a simple rectagu1arlaminated piece of steel with the tr

6、ansformer windings 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

7、 type of construction is known as shell form. In either case，the core is constructed of thin laminations electrically isolate</p><p>　　The primary and secondary windings in a physical transformer are wrapped

8、 one on top of the other with the low-voltage winding innermost．Such an arrangement serves two purposes：1.It simplifies the problem of insulating the high-voltage winding from the core．2.It results in much less leakage f

9、lux than would be the two windings were separated by a distance on the core．</p><p>　　Power transformers are given a variety of different names, depending on their use in power systems. A transformer connect

10、ed to the output of a generator and used to step its vo1tage up 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 tr

11、ansmission levels to distribution levels is called a substation transformer. Finally，the transformer that takes the distribution voltage and steps it down to t</p><p>　　In addition to the various power trans

12、formers，two special-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 vo1tage and produce a low secondary vo1t

13、age directly proportional to it. Such a transformer is called a potential transformer．A power transformer also produces a secondary vo1tage directly proportional to its primary voltage; the difference between a potential

14、 transformer and a pow</p><p>　　The Directional Protection Basis</p><p>　　Early attempts to improve power-service reliability to loads remote from generation led to the dual-1ine concept．Of cour

15、se，it is possible to build two 1ines to a load，and switch the load to whichever line remains energized after a di51urbance．But better service continuity will be available if both lines normally feed the load and only the

16、 faulted line is tripped when disturbances occur．Fig.1-l shows a sing1e-generator，two-1ine,single-load system with breakers properly arranged to supply the load</p><p>　　The magnitude of the fault current th

17、rough breakers B and D is the same，regardless of the location of the fault on the line terminal of breaker B or D．Therefore relay coordination must be based on characteristics other than a time delay that starts from th

18、e time of the fault. Observe that the direction of current flowing through either breaker B or D is a function of which line the fault is on. Thus for a fault on the line between A and B, the current flows out of the lo

19、ad bus through breaker </p><p>　　Relay coordination for the system shown in Fig．1-l can now be achieved by the installation of directional over current time delay relays on breakers B and D．Breakers A and C

20、can have non directional over current time delay relays．They may also now have instantaneous relays applied．The relays would be set as follows：The directional relays could be set with no intentional time delay. They will

21、 have inherent time delay．The time delay over current relays on breakers A and C would have current settin</p><p><b>　　Load</b></p><p><b>　　Fig.1-1</b></p><p&g

22、t;　　Direction of current flow on an a. c. system is determined by comparing the current vector with some other reference vector，such as a voltage vector．In the systems of Fig.1-1 the reference vo1tage vector would be der

23、ived from the voltages on the load bus．Direction of current or power flow cannot be determined instantaneously on a．c．systems whose lines and equipment contain reactance．This is apparent from the fact that when vo1tage e

24、xists, the lagging current can be plus or minus or zero，dependin</p><p><b>　　變壓器的類(lèi)型及結(jié)構(gòu)</b></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)繞在鐵氧體上的繞組構(gòu)成．通常，繞組之間不直接相連，它們是通過(guò)鐵芯內(nèi)部的主磁通相連接

25、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。如有第三個(gè)繞組，稱(chēng)之為第三繞組。</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

26、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。鐵芯片之間相互絕緣，以最大限度地降低渦流。</p><p>　　在實(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，低壓繞組在最里面。此類(lèi)結(jié)構(gòu)安排有二個(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)少得多。</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

27、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。在輸電線(xiàn)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

28、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)的電流要小的多的二次側(cè)電流，且使二次側(cè)的電流與一次側(cè)的電流成比例。此類(lèi)裝置稱(chēng)為電流互感器。</p><p><b>　　方向保護(hù)基礎(chǔ)</b></p><p>　　早期

29、，對(duì)于遠(yuǎn)離發(fā)電站的用戶(hù)，為改善其供電可靠性提出了雙回線(xiàn)供電的設(shè)想。當(dāng)然，也可以架設(shè)不同的兩回線(xiàn)給用戶(hù)供電。在系統(tǒng)發(fā)生故障后，把用戶(hù)切換至任一條正常的線(xiàn)路。但更好的連續(xù)供電方式是正常以雙回線(xiàn)同時(shí)供電。當(dāng)發(fā)生故障時(shí)，只斷開(kāi)故障線(xiàn)。圖1—1所示為一個(gè)單電源、單負(fù)載、雙回輸電線(xiàn)系統(tǒng)。對(duì)該系統(tǒng)配置合適的斷路器后，當(dāng)一回線(xiàn)發(fā)生故隨時(shí)，仍可對(duì)負(fù)載供電。為使這種供電方式更為有效，還需配置合適的繼電保護(hù)系統(tǒng)，否則，昂貴的電力設(shè)備不能發(fā)揮其預(yù)期的作用?？梢?/p>

30、考慮在四個(gè)斷路器上裝設(shè)瞬時(shí)和延時(shí)起動(dòng)繼電器。顯然，這種類(lèi)型的繼電器無(wú)法對(duì)所有線(xiàn)路故障進(jìn)行協(xié)調(diào)配合。例如，故障點(diǎn)在靠近斷路器D的線(xiàn)路端，D跳閘應(yīng)比B快，反之，B應(yīng)比D快。顯然，如果要想使繼電器配合協(xié)調(diào)，繼電保護(hù)工程師必須尋求除了延時(shí)以外的其他途徑。</p><p>　　無(wú)論故障點(diǎn)靠近斷路器B或D的哪一端，流過(guò)斷路器B和D的故障電流大小是相同的。因此繼電保護(hù)的配合必須以此為基礎(chǔ)，而不是放在從故障開(kāi)始啟動(dòng)的延時(shí)上。我們

31、觀(guān)察通過(guò)斷路器B或D的電流方向是隨故障點(diǎn)發(fā)生在哪一條線(xiàn)路上變化的。對(duì)于A和B之間的線(xiàn)路上的故障，通過(guò)斷路器B的電流方向?yàn)閺呢?fù)載母線(xiàn)流向故障點(diǎn)。對(duì)于斷路器D，電流通過(guò)斷路器流向負(fù)載母線(xiàn)。在這種情況下，斷路器B應(yīng)跳閘，D不應(yīng)跳閘。要達(dá)到這個(gè)目的，我們可在斷路器B和D上裝設(shè)方向繼電器，該方向繼電器的聯(lián)接應(yīng)保證只有當(dāng)通過(guò)它們的電流方向?yàn)殡x開(kāi)母線(xiàn)時(shí)才起動(dòng)。</p><p><b>　　圖1-1</b>

32、</p><p>　　對(duì)于圖14—1所示的系統(tǒng)，在斷路器B和D裝設(shè)了方向過(guò)流延時(shí)繼電器后，繼電器的配合才能實(shí)現(xiàn)。斷路器A和C裝設(shè)無(wú)方向的過(guò)流延時(shí)繼電器及瞬時(shí)動(dòng)作的電流繼電器。各個(gè)繼電器整定配合如下：方向繼電器不能設(shè)置延時(shí)，它們只有本身固有的動(dòng)作時(shí)間。A和C的延時(shí)過(guò)流繼電器通過(guò)電流整定使它們作為負(fù)載母線(xiàn)或負(fù)載設(shè)備故障的后備保護(hù)。斷路器A和C的瞬時(shí)動(dòng)作元件通過(guò)電流整定使它們?cè)谪?fù)載母線(xiàn)故障時(shí)不動(dòng)作。于是快速保護(hù)可以保護(hù)

33、發(fā)電機(jī)和負(fù)載之間線(xiàn)路長(zhǎng)度的大部分。從圖中我們還可看到，在斷路器A或C的線(xiàn)路側(cè)發(fā)生的故障使發(fā)電機(jī)電壓崩潰，在斷路器A和C上的瞬時(shí)繼電器不能真正瞬時(shí)切除故陳，因?yàn)殡娏υO(shè)備動(dòng)作需要時(shí)間，在這個(gè)期間內(nèi)，流過(guò)斷路器B和D的電流很小甚至為0，因此在這種故障狀態(tài)下，只有等到發(fā)電廠(chǎng)有關(guān)的斷路器動(dòng)作后，斷路器B和D才動(dòng)作。這就是我們所說(shuō)的順序跳閘，通常在上述情況下這樣做是允許的。</p><p>　　在一個(gè)交流系統(tǒng)中，通過(guò)電流矢量

34、與其他參考矢量(例如電壓矢量)的比較，可以確定電流的方向。圖1—1所示系統(tǒng)的參考矢量可從負(fù)載母線(xiàn)電壓矢量推出。由于在該交流系統(tǒng)中，線(xiàn)路和設(shè)備含有電抗，電流和功率的瞬時(shí)方向不能確定，這是顯而易見(jiàn)的，因?yàn)楫?dāng)有電壓時(shí)，相位落后的電流取樣的瞬時(shí)值取決于它在電壓周期中的碑間，可能為正，也可能為負(fù)或?yàn)榱恪Ｒ虼?，電壓、電流失量必須在一個(gè)時(shí)間間隔內(nèi)采樣。為了較為準(zhǔn)確的采樣，時(shí)間間隔可從一個(gè)半周期到一個(gè)周期。目前正在進(jìn)行更短時(shí)間的采樣的研究工作。這個(gè)研究