外文翻譯--變壓器的類型及結構

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>　　變壓器的類型及結構</b></p><p>　　變壓器是通過磁場作用將交流電從某一電壓等級轉換至另一電壓等級的設備。它由兩個或多個繞在鐵氧體上的繞組構成．通常，繞組之間不直接相連，它們是通過鐵芯內部的主磁通相連接

25、的。</p><p>　　變壓器的一個繞組與交流電源連接，第二個繞組(也許第三個繞組)為負載提供電功率。與電源連接的繞組稱為一次繞組或輸入繞組。與負載連接的繞組稱為二次繞組或輸出繞組。如有第三個繞組，稱之為第三繞組。</p><p>　　變壓器的鐵芯分為兩類。一類是由繞組纏繞在一個簡單的矩形鋼片疊成的鐵芯兩邊而構成。此類結構的繞組稱為鐵芯式結構。另一類是由三個分支的鋼片疊成，繞組繞在中間的

26、一個分支上。此類結構稱為框式結構。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>　　在實際的變壓器中，一次繞組和二次繞組一個在另一個的外面，低壓繞組在最里面。此類結構安排有二個目的：①使高壓繞組與鐵芯之間相互絕緣；②使漏磁通較二個繞組相互隔開時少得多。</p><p>　　在電力系統(tǒng)中，根據不同的用途，電力變壓器有許多種不同的

27、名稱。與發(fā)電機連接并將其電壓提高到電網電壓的變壓器被稱為升壓變壓。在輸電線另一端，將電網電壓降至配電電壓的變壓器稱為降壓變壓器。最后，把電壓降低到能實際應用量級的變壓器稱為配電變壓器。以上變壓器的結構基本相同，唯一的區(qū)別在于各自的實際用途不同。</p><p>　　除了上述多種變壓器之外，在電機與電力系統(tǒng)中還使用兩種特殊用途的變壓器。第一種專門設計的變壓器是用來采樣電壓，并產生一個低的二次電壓，該電壓與所采樣的電

28、壓成正比。此類變壓器稱為電壓互感器。功率變壓器中產生的二次側的電壓也與一次側的電壓成正比。但電壓互感器與電力變壓器的不同在于電壓互感器設計為僅處理較小的電流。第二種專門設計的變壓器設計成為用來提供比一次側的電流要小的多的二次側電流，且使二次側的電流與一次側的電流成比例。此類裝置稱為電流互感器。</p><p><b>　　方向保護基礎</b></p><p>　　早期

29、，對于遠離發(fā)電站的用戶，為改善其供電可靠性提出了雙回線供電的設想。當然，也可以架設不同的兩回線給用戶供電。在系統(tǒng)發(fā)生故障后，把用戶切換至任一條正常的線路。但更好的連續(xù)供電方式是正常以雙回線同時供電。當發(fā)生故障時，只斷開故障線。圖1—1所示為一個單電源、單負載、雙回輸電線系統(tǒng)。對該系統(tǒng)配置合適的斷路器后，當一回線發(fā)生故隨時，仍可對負載供電。為使這種供電方式更為有效，還需配置合適的繼電保護系統(tǒng)，否則，昂貴的電力設備不能發(fā)揮其預期的作用?？梢?/p>

30、考慮在四個斷路器上裝設瞬時和延時起動繼電器。顯然，這種類型的繼電器無法對所有線路故障進行協調配合。例如，故障點在靠近斷路器D的線路端，D跳閘應比B快，反之，B應比D快。顯然，如果要想使繼電器配合協調，繼電保護工程師必須尋求除了延時以外的其他途徑。</p><p>　　無論故障點靠近斷路器B或D的哪一端，流過斷路器B和D的故障電流大小是相同的。因此繼電保護的配合必須以此為基礎，而不是放在從故障開始啟動的延時上。我們

31、觀察通過斷路器B或D的電流方向是隨故障點發(fā)生在哪一條線路上變化的。對于A和B之間的線路上的故障，通過斷路器B的電流方向為從負載母線流向故障點。對于斷路器D，電流通過斷路器流向負載母線。在這種情況下，斷路器B應跳閘，D不應跳閘。要達到這個目的，我們可在斷路器B和D上裝設方向繼電器，該方向繼電器的聯接應保證只有當通過它們的電流方向為離開母線時才起動。</p><p><b>　　圖1-1</b>

32、</p><p>　　對于圖14—1所示的系統(tǒng)，在斷路器B和D裝設了方向過流延時繼電器后，繼電器的配合才能實現。斷路器A和C裝設無方向的過流延時繼電器及瞬時動作的電流繼電器。各個繼電器整定配合如下：方向繼電器不能設置延時，它們只有本身固有的動作時間。A和C的延時過流繼電器通過電流整定使它們作為負載母線或負載設備故障的后備保護。斷路器A和C的瞬時動作元件通過電流整定使它們在負載母線故障時不動作。于是快速保護可以保護

33、發(fā)電機和負載之間線路長度的大部分。從圖中我們還可看到，在斷路器A或C的線路側發(fā)生的故障使發(fā)電機電壓崩潰，在斷路器A和C上的瞬時繼電器不能真正瞬時切除故陳，因為電力設備動作需要時間，在這個期間內，流過斷路器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)電廠有關的斷路器動作后，斷路器B和D才動作。這就是我們所說的順序跳閘，通常在上述情況下這樣做是允許的。</p><p>　　在一個交流系統(tǒng)中，通過電流矢量

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)的參考矢量可從負載母線電壓矢量推出。由于在該交流系統(tǒng)中，線路和設備含有電抗，電流和功率的瞬時方向不能確定，這是顯而易見的，因為當有電壓時，相位落后的電流取樣的瞬時值取決于它在電壓周期中的碑間，可能為正，也可能為負或為零。因此，電壓、電流失量必須在一個時間間隔內采樣。為了較為準確的采樣，時間間隔可從一個半周期到一個周期。目前正在進行更短時間的采樣的研究工作。這個研究