外文翻譯---負(fù)載運(yùn)行的變壓器

1、<p>　　畢業(yè)設(shè)計(jì)（論文）外文文獻(xiàn)譯文</p><p><b>　　負(fù)載運(yùn)行的變壓器</b></p><p>　　通過選擇合適的匝數(shù)比，一次側(cè)輸入電壓可任意轉(zhuǎn)換成所希望的二次側(cè)開路電壓?？捎糜诋a(chǎn)生負(fù)載電流，該電流的幅值和功率因數(shù)將由而次側(cè)電路的阻抗決定?，F(xiàn)在，我們要討論一種滯后功率因數(shù)。二次側(cè)電流及其總安匝將影響磁通，有一種對(duì)鐵芯產(chǎn)生去磁、減小和的趨向。因

2、為一次側(cè)漏阻抗壓降如此之小，所以的微小變化都將導(dǎo)致一次側(cè)電流增加很大，從增大至一個(gè)新值。增加的一次側(cè)電流和磁勢(shì)近似平衡了全部二次側(cè)磁勢(shì)。這樣的話，互感磁通只經(jīng)歷很小的變化，并且實(shí)際上只需要與空載時(shí)相同的凈磁勢(shì)。一次側(cè)總磁勢(shì)增加了，它是平衡同量的二次側(cè)磁勢(shì)所必需的。在向量方程中，，上式也可變換成。滿載時(shí)，電流只約占滿載電流的5%，因而近似等于。記住，近似等于的輸入容量也就近似等于輸出容量。</p><p>　　一次

3、側(cè)電流已增大，隨之與之成正比的一次側(cè)漏磁通也增大。交鏈一次繞組的總磁通沒有變化，這是因?yàn)榭偡措妱?dòng)勢(shì)仍然與相等且反向。然而此時(shí)卻存在磁通的重新分配，由于隨的增加而增加，互感磁通分量已經(jīng)減小。盡管變化很小，但是如果沒有互感磁通和電動(dòng)勢(shì)的變化來允許一次側(cè)電流變化，那么二次側(cè)的需求就無法滿足。交鏈二次繞組的凈磁通由于產(chǎn)生的二次側(cè)漏磁通（其與反相）的建立而被進(jìn)一步削弱。盡管圖中和是分開表示的，但它們?cè)阼F芯中是一個(gè)合成量，該合成量在圖示中的瞬時(shí)是向

4、下的。這樣，二次側(cè)端電壓降至，它可被看成兩個(gè)分量，即，或者向量形式。與一次側(cè)漏磁通一樣，的作用也用一個(gè)大體為常數(shù)的漏電感來表征。要注意的是，由于它對(duì)互感磁通的作用，一次側(cè)漏磁通對(duì)于二次側(cè)端電壓的變化產(chǎn)生部分影響。這兩種漏磁通，緊密相關(guān)；例如，對(duì)的去磁作用引起了一次側(cè)的變化，從而導(dǎo)致了一次側(cè)漏磁通的產(chǎn)生。</p><p>　　如果我們討論一個(gè)足夠低的超前功率因數(shù)，二次側(cè)總磁通和互感磁通都會(huì)增加，從而使得二次側(cè)端電壓

5、隨負(fù)載增加而升高。在空載情形下，如果忽略電阻，幅值大小不變，因?yàn)樗蕴峁┮粋€(gè)等于的反總電動(dòng)勢(shì)。盡管現(xiàn)在是一次側(cè)和二次側(cè)磁勢(shì)的共同作用產(chǎn)生的，但它實(shí)際上與相同。互感磁通必須仍隨負(fù)載變化而變化以改變，從而產(chǎn)生更大的一次側(cè)電流。此時(shí)的幅值已經(jīng)增大，但由于與是向量合成，因此一次側(cè)電流仍然是增大的。</p><p>　　從上述圖中，還應(yīng)得出兩點(diǎn)：首先，為方便起見已假設(shè)匝數(shù)比為1，這樣可使。其次，如果橫軸像通常取的話，那么向

6、量圖是以為零時(shí)間參數(shù)的，圖中各物理量時(shí)間方向并不是該瞬時(shí)的。在周期性交變中，有一次側(cè)漏磁通為零的瞬時(shí)，也有二次側(cè)漏磁通為零的瞬時(shí)，還有它們處于同一方向的瞬時(shí)。</p><p>　　已經(jīng)推出的變壓器二次側(cè)繞組端開路的等效電路，通過加上二次側(cè)電阻和漏抗便可很容易擴(kuò)展成二次側(cè)負(fù)載時(shí)的等效電路。</p><p>　　實(shí)際中所有的變壓器的匝數(shù)比都不等于1，盡管有時(shí)使其為1也是為了使一個(gè)電路與另一個(gè)在

7、相同電壓下運(yùn)行的電路實(shí)現(xiàn)電氣隔離。為了分析時(shí)的情況，二次側(cè)的反應(yīng)得從一次側(cè)來看，這種反應(yīng)只有通過由二次側(cè)的磁勢(shì)產(chǎn)生磁場(chǎng)力來反應(yīng)。我們從一次側(cè)無法判斷是大，小，還是小，大，正是電流和匝數(shù)的乘積在產(chǎn)生作用。因此，二次側(cè)繞組可用任意個(gè)在一次側(cè)產(chǎn)生相同匝數(shù)的等效繞組是方便的。</p><p>　　當(dāng)變換成，由于電動(dòng)勢(shì)與匝數(shù)成正比，所以，與相等。</p><p>　　對(duì)于電流，由于對(duì)一次側(cè)作用的安匝

8、數(shù)必須保持不變，因此，即。</p><p>　　對(duì)于阻抗，由于二次側(cè)電壓變成，電流變?yōu)?，因此阻抗值，包括?fù)載阻抗必然變?yōu)?。因此，，?lt;/p><p>　　如果將一次側(cè)匝數(shù)作為參考匝數(shù)，那么這種過程稱為往一次側(cè)的折算。</p><p>　　我們可以用一些方法來驗(yàn)證上述折算過程是否正確。</p><p>　　例如，折算后的二次繞組的銅耗必須與原二

9、次繞組銅耗相等，否則一次側(cè)提供給其損耗的功率就變了。必須等于，而事實(shí)上確實(shí)簡(jiǎn)化成了。</p><p>　　類似地，與成比例的漏磁場(chǎng)的磁場(chǎng)儲(chǔ)能，求出后驗(yàn)證與成正比。折算后的二次側(cè)。</p><p>　　盡管看起來似乎不可理解，事實(shí)上這種論點(diǎn)是可靠的。實(shí)際上，如果我們將實(shí)際的二次繞組當(dāng)真從鐵芯上移開，并用一個(gè)參數(shù)設(shè)計(jì)成，，，的等效繞組和負(fù)載電路替換，在正常電網(wǎng)頻率運(yùn)行時(shí)，從一次側(cè)兩端無法判斷二

10、次側(cè)的磁勢(shì)、所需容量及銅耗與前有何差別。</p><p>　　在選擇折算基準(zhǔn)時(shí)，無非是將一次側(cè)與折算后的二次側(cè)匝數(shù)設(shè)為相等，除此之外再?zèng)]有什么更要緊的了。但有時(shí)將一次側(cè)折算到二次側(cè)倒是方便的，在這種情況下，如果所有下標(biāo)“1”的量都變換成了下標(biāo)“2”的量，那么很容易得到必需的折算系數(shù)，例如。值得注意的是，對(duì)于一臺(tái)實(shí)際的變壓器，，；同樣地，。</p><p>　　的通常情形時(shí)的等效電路，它除了

11、為了考慮鐵耗而引入了，且為了將折算回而在二次側(cè)兩端引入了一理想的無損耗轉(zhuǎn)換外，其他方面是一樣的。在運(yùn)用這種理想轉(zhuǎn)換之前，內(nèi)部電壓和功率損耗已進(jìn)行了計(jì)算。當(dāng)在電路中選擇了適當(dāng)?shù)膮?shù)時(shí)，在一、二次側(cè)兩端測(cè)得的變壓器運(yùn)行情況與在該電路相應(yīng)端所測(cè)得的請(qǐng)況是完全一致的。將線圈和線圈并排放置在一個(gè)鐵芯的兩邊，這一點(diǎn)與實(shí)際情況之間的差別僅僅是為了方便。當(dāng)然，就變壓器本身來說，兩線圈是繞在同一鐵芯柱上的。</p><p>　　如

12、果將激磁支路移至一次繞組端口，引起的誤差很小，但一些不合理的現(xiàn)象又會(huì)發(fā)生。例如，流過一次側(cè)阻抗的電流不再是整個(gè)一次側(cè)電流。由于通常只是的很小一部分，所有誤差相當(dāng)小。對(duì)一個(gè)具體問題可否允許有細(xì)微差別的回答取決于是否允許這種誤差的存在。對(duì)于這種簡(jiǎn)化電路，一次側(cè)和折算后二次側(cè)阻抗可相加，得和</p><p>　　需要指出的是，在此得到的等效電路僅僅適用于電網(wǎng)頻率下的正常運(yùn)行；一旦電壓變化率產(chǎn)生相當(dāng)大的電容電流時(shí)必須考慮

13、電容效應(yīng)。這對(duì)于高電壓和頻率超過100Hz的情形是很重要的。其次，即使是對(duì)于電網(wǎng)頻率也并非唯一可行的等效電路。另一種形式是將變壓器看成一個(gè)三端或四端網(wǎng)絡(luò)，這樣便產(chǎn)生一個(gè)準(zhǔn)確的表達(dá)，它對(duì)于那些把所有裝置看成是具有某種傳遞性能的電路元件的工程師來說是方便的。以此為分析基礎(chǔ)的電路會(huì)擁有一個(gè)既產(chǎn)生電壓大小的變化，也產(chǎn)生相位移的匝比，其阻抗也會(huì)與繞組的阻抗不同。這種電路無法解釋變壓器內(nèi)類似飽和效應(yīng)等現(xiàn)象。</p><p>

14、　　等效電路有兩個(gè)入端口形式：</p><p>　　從一次側(cè)看為一個(gè)U形電路，其折合后的負(fù)載阻抗的端電壓為；</p><p>　　從二次側(cè)看為一其值為，且伴有由和引起內(nèi)壓降的恒壓源。在這種電路中有時(shí)可省略激磁支路，這樣電路簡(jiǎn)化為一臺(tái)產(chǎn)生恒值電壓（實(shí)際上等于）并帶有阻抗（實(shí)際上等于）的發(fā)電機(jī)。</p><p>　　在上述兩種情況下，參數(shù)都可折算到二次繞組，這樣可減小計(jì)

15、算時(shí)間。</p><p>　　其電阻和電抗值可通過兩種簡(jiǎn)單的輕載試驗(yàn)獲得。</p><p><b>　　外文文獻(xiàn)原文</b></p><p>　　The Transformer on load</p><p>　　It has been shown that a primary input voltage can be

16、 transformed to any desired open-circuit secondary voltage by a suitable choice of turns ratio. is available for circulating a load current impedance. For the moment, a lagging power factor will be considered. The secon

17、dary current and the resulting ampere-turns will change the flux, tending to demagnetize the core, reduce and with it . Because the primary leakage impedance drop is so low, a small alteration to will cause an appreci

18、able i</p><p>　　The physical current has increased, and with in the primary leakage flux to which it is proportional. The total flux linking the primary ,, is shown unchanged because the total back e.m.f.,（）

19、is still equal and opposite to . However, there has been a redistribution of flux and the mutual component has fallen due to the increase of with . Although the change is small, the secondary demand could not be met wit

20、hout a mutual flux and e.m.f. alteration to permit primary current to change. The net flu</p><p>　　If a low enough leading power factor is considered, the total secondary flux and the mutual flux are increas

21、ed causing the secondary terminal voltage to rise with load. is unchanged in magnitude from the no load condition since, neglecting resistance, it still has to provide a total back e.m.f. equal to . It is virtually the

22、same as , though now produced by the combined effect of primary and secondary ampere-turns. The mutual flux must still change with load to give a change of and permit more</p><p>　　Two more points should be

23、 made about the figures. Firstly, a unity turns ratio has been assumed for convenience so that . Secondly, the physical picture is drawn for a different instant of time from the vector diagrams which show , if the horizo

24、ntal axis is taken as usual, to be the zero time reference. There are instants in the cycle when primary leakage flux is zero, when the secondary leakage flux is zero, and when primary and secondary leakage flux is zero,

25、 and when primary and secondary lea</p><p>　　The equivalent circuit already derived for the transformer with the secondary terminals open, can easily be extended to cover the loaded secondary by the addition

26、 of the secondary resistance and leakage reactance.</p><p>　　Practically all transformers have a turns ratio different from unity although such an arrangement is sometimes employed for the purposes of electr

27、ically isolating one circuit from another operating at the same voltage. To explain the case where the reaction of the secondary will be viewed from the primary winding. The reaction is experienced only in terms of the

28、magnetizing force due to the secondary ampere-turns. There is no way of detecting from the primary side whether is large and small o</p><p>　　With changes to , since the e.m.f.s are proportional to turns,

29、 which is the same as .</p><p>　　For current, since the reaction ampere turns must be unchanged must be equal to .i.e. .</p><p>　　For impedance , since any secondary voltage becomes , and sec

30、ondary current becomes , then any secondary impedance, including load impedance, must become . Consequently, and .</p><p>　　If the primary turns are taken as reference turns, the process is called referring

31、 to the primary side.</p><p>　　There are a few checks which can be made to see if the procedure outlined is valid.</p><p>　　For example, the copper loss in the referred secondary winding must be

32、 the same as in the original secondary otherwise the primary would have to supply a different loss power. must be equal to . does in fact reduce to .</p><p>　　Similarly the stored magnetic energy in the le

33、akage field which is proportional to will be found to check as . The referred secondary .</p><p>　　The argument is sound, though at first it may have seemed suspect. In fact, if the actual secondary windin

34、g was removed physically from the core and replaced by the equivalent winding and load circuit designed to give the parameters ,,and , measurements from the primary terminals would be unable to detect any difference in s

35、econdary ampere-turns, demand or copper loss, under normal power frequency operation.</p><p>　　There is no point in choosing any basis other than equal turns on primary and referred secondary, but it is som

36、etimes convenient to refer the primary to the secondary winding. In this case, if all the subscript 1’s are interchanged for the subscript 2’s, the necessary referring constants are easily found; e.g. ,; similarly and .&

37、lt;/p><p>　　The equivalent circuit for the general case where except that has been added to allow for iron loss and an ideal lossless transformation has been included before the secondary terminals to return

38、 to .All calculations of internal voltage and power losses are made before this ideal transformation is applied. The behaviour of a transformer as detected at both sets of terminals is the same as the behaviour detected

39、at the corresponding terminals of this circuit when the appropriate parameters are</p><p>　　Very little error is introduced if the magnetising branch is transferred to the primary terminals, but a few anomal

40、ies will arise. For example ,the current shown flowing through the primary impedance is no longer the whole of the primary current. The error is quite small since is usually such a small fraction of . Slightly different

41、 answers may be obtained to a particular problem depending on whether or not allowance is made for this error. With this simplified circuit, the primary and referred</p><p><b>　　and </b></p>

42、;<p>　　It should be pointed out that the equivalent circuit as derived here is only valid for normal operation at power frequencies; capacitance effects must be taken into account whenever the rate of change of vo

43、ltage would give rise to appreciable capacitance currents, . They are important at high voltages and at frequencies much beyond 100 cycles/sec. A further point is not the only possible equivalent circuit even for power f

44、requencies .An alternative , treating the transformer as a three-or four-t</p><p>　　There are two ways of looking at the equivalent circuit:</p><p>　　viewed from the primary as a sink but the re

45、ferred load impedance connected across ,or</p><p>　　viewed from the secondary as a source of constant voltage with internal drops due to and . The magnetizing branch is sometimes omitted in this representa

46、tion and so the circuit reduces to a generator producing a constant voltage (actually equal to ) and having an internal impedance (actually equal to ).</p><p>　　In either case, the parameters could be refer