交流電外文翻譯

1、<p><b>　　附錄</b></p><p>　　附錄A 外文翻譯—原文部分</p><p>　　Alternating Current</p><p>　　An alternating current is one which varies in the circuit with time. The value of the c

2、urrent at any given instant of time is the instantaneous value of current, symbolized by . The instantaneous value of current is deemed positive for one direction of flow though the cross-section of a conductor, and neg

3、ative for the opposite direction. The direction of current flow in which instantaneous values are positive is called positive. A current is fully specified, if one knows its instantaneous value</p><p>　　Curr

4、ent whose value recur for equal increments of time are called periodic, and the least increment of time for which this recurrent takes place is called the period . For a periodic current = F(t)= F(t+T)&l

5、t;/p><p>　　Fig.4.1 shows an example of the relationship = F(t) for a periodic current. The arrow in the diagram indicates the positive direction of current flow. The dotted arrows show the actual direction of c

6、urrent flow at the instants of time when >0 and <0. The segments of the curve between points a and b or O and c cover a complete cycle of current alternations over one period.</p><p>　　The number of cy

7、cle or period per second is the frequency of a periodic current. It is reciprocal of its period.</p><p>　　It is usually to specify the frequency of any periodic quantity in cycle per second. Thus the frequen

8、cy of a periodic current will be 1 cycle per second, if its period is second, or 1cycle/sec.A direct current may be regarded as a special case of a periodic current whose period is infinitely long and the frequency is th

9、us zero.</p><p>　　The term alternating current is often used in the narrow sense of a periodic current whose constant(direction-current)component is zero, or </p><p>　　The frequencies of alterna

10、ting current encountered in practice range over wide values. The mains frequency is 50Hz in the Soviet Union and Europe, and 60Hz in the United States. Some industrial processes use frequencies from 10Hz toHz .In radio p

11、ractice, frequencies up to Hz are employed.</p><p>　　The definitions for current just introduced(and, indeed, those that will be introduced shortly) fully apply to periodic voltages, e.m.f.s, magnetic fluxes

12、 and any other electrical and magnetic quantities. Some additional remarks are only needed with regard to the sign of alternating voltage and e.m.f.s.</p><p>　　An alternating voltage between two point A and

13、B, determined along a specified path 1, periodically changes sign, so that if it is assumed to be positive in the direction from A to B. it will be negative in direction from B to A at the same instant of time. This is w

14、hy it is important to label which of the two directions is assumed positive. In diagrams, such a direction is labeled either by arrows or subscripts in the symbols for voltage and is regarded to be the positive reference

15、 direction of</p><p>　　Electrical engineering uses the simplest and commonest type of alternating current, the one which varies sinusoidally with time; hence the term a harmonic or a sinusoidal current. The

16、preference for sinusoidal currents is explained modulated by the signal in amplitude, frequency or phase. Periodic non-sinusoidal current may likewise be treated as composed of sinusoidal current at a variety of frequenc

17、ies occurring simultaneously. This is why thorough of sinusoidal-current circuits is of primary </p><p>　　The A.C Generator</p><p>　　An A.C generator consists of a stationary part, the stator, a

18、nd a revolving part, the rotor. As a rule the rotor carries magnetic poles with coils around them. These are the filed coils of the generator ,because they establish a magnetic filed in the machine. They are energized wi

19、th direct current through slip rings and brushes. The slots of the stator staked up from electrical-sheet steel punchings receive the coils of the stator winding. The stator coils are connected in series, as shown by th&

20、lt;/p><p>　　The e.m.f. induced in a stator conductor is given by</p><p>　　where —magnetic induction of the field moving relative to the conductor;</p><p>　　—active length of the conduc

21、tor;</p><p>　　—speed with which the magnetic field moves relative to the conductor.</p><p>　　Since and are constant, the induced e.m.f. will vary exactly as varies. If the induced e.m.f is to

22、 be sinusoidal(which is usually sought), the distribution of around the circumference of the stator should be as close to sinusoidal as practicable.</p><p>　　With pole-pairs on the rotor, the e.m.f. will un

23、dergo cycles of changes every revolution. If the speed of the rotor is revolutions per minutes (r/min), this works out to cycles per minute, and the frequency of the induced e.m.f. is： </p><p>　　For

24、f=50Hz, the rotor of a generator with one pair of poles should run at 3000r/min.And with two pole-pairs, at 1500r/min. With speeds like this, rotors are usually fabricated with non-salient piles for greater mechanical st

25、rength.</p><p>　　High-frequency generators operating at 800 to 8000Hz are all of special designs. Their uses are in the heat-treatment and induction-heating field. Still higher frequencies are generated by v

26、alve and semiconductor oscillators.</p><p>　　Sinusoidal Current</p><p>　　The instantaneous value of a sinusoidal current is given by</p><p>　　where is the peak value or amplitude o

27、f the current, and is the phase of the current. The quantity is the initial phase of the current (for t=0) and is termed the epoch angle. The phase of a current continuously increases with time. When it has increase by

28、 , the whole cycle of changes is repeated exactly all over again. Therefore, s peaking of the phase of a current, it is customary to drop the integer and to consider the phase within or between zero and .</p>&l

29、t;p>　　The above change of phase by occurs during the period T. therefore, the rate of change of the phase is given by . It is symbolized by the Greek letter (omega) and is called the pulsatance. Noting that , we may

30、write</p><p>　　The above expression, relating and ,has been responsible for the fact that the pulstance is also termed the angular velocity or frequency. It is expressed in radians per second. Thus, for ,

31、 . Introduce in Eq.(4.1) we obtain</p><p>　　Sinusoidal current of the same frequency, but differing in amplitude and epoch angles, are shown in Fig.4.2. their instantaneous values are</p><p>　　

32、The time or the product ,proportional to time, is laid off as abscissa.</p><p>　　The epoch angle is always measured between the origin of coordinates, which corresponds to the reference time t=0, and the in

33、stant when a given sinusoidal just passes through zero(from negative to positive values). For >0, the start(or zero point) of the sinusoid is shifted to the left, and for <0 it is shifted to the right of the origi

34、n of coordinates.</p><p>　　Alternatively, the instantaneous value of a sinusoidal current may be represented by a cosinusoidal function of the form</p><p><b>　　)</b></p><p

35、><b>　　Where .</b></p><p>　　When two or more sinusoidal function differ in time phase as reckoned from similar points, they are said to be shifted or displaced in phase with respect to one anot

36、her. This phase shift, or the phase displacement, is measured between their respective zeros, and obviously is the difference in epoch angles. Referring to Fig.4.3, , and the current is said to lead the current in phas

37、e by , or, which is the same, the current lags in phase behind the current by .</p><p>　　Two sinusoidal functions of the same frequency are said to be in phase if they have same epoch angle, and are said t

38、o be in anti-phase when their phase displacement is . Finally, they are said to be in quadrature if their difference is .</p><p>　　附錄B 外文翻譯——譯文部分</p><p><b>　　交流電</b></p><p

39、>　　交流電在電路中是一個隨時間變化的值。電流值在任何給定的時間上都是一個瞬態(tài)值，用符號表示。當(dāng)瞬態(tài)電流值從用正號標(biāo)記的導(dǎo)體的端流進(jìn)時為正值，而從相反的方向流動時為負(fù)值。當(dāng)電流的任一瞬態(tài)值為正時，它流進(jìn)導(dǎo)體的方向就為正極。假如知道瞬態(tài)值與時間的關(guān)系式：以及它的正方向，那么瞬時電流值就是一個定值。</p><p>　　電流值隨時間T進(jìn)行周期性變化的這種現(xiàn)象叫做交流電的周期性，能滿足這個條件的最小T值我們把它叫

40、做周期。周期電流的公式為：</p><p>　　= F(t)= F(t+T)</p><p>　　圖4.1是= F(t)周期電流的一個例子。正如圖表中箭頭所示，指出的方向表示電流的方向。打點(diǎn)的箭頭表示瞬時電流的正方向。在曲線上a與b或者o與c之間的部分就表示交流電一個完整的周期。</p><p>　　周期的倒數(shù)是為電流的頻率。表示為：</p><

41、p>　　通常把頻率描述成周期值的倒數(shù)。因此交流電的頻率就表示成多少周期/秒。直流電可以被認(rèn)為是交流電的一個特例，是周期無限長，頻率為0的交流電。</p><p>　　時間有限的交流電通常被認(rèn)為是狹義的交流電，因?yàn)樗某Ａ恐凳?或表示為</p><p>　　交流電的頻率在現(xiàn)實(shí)生活中通?？梢匀『艽蠓秶鷥?nèi)的值。在前蘇聯(lián)和歐洲工頻為50Hz,在美國為60Hz.一些工業(yè)用電頻率往往在10到Hz

42、不等。在無線電波中，甚至有用Hz的。</p><p>　　引用前面對電流的定義（確實(shí)，只是很簡單的介紹）來介紹電壓，電動勢, 磁通以及其他電氣與磁的量值。一些附加的參數(shù)只是在描述電壓和電動勢才用得上。</p><p>　　A,B兩點(diǎn)之間的電壓，由路徑?jīng)Q定其值是正或是負(fù)，是周期性改變的，當(dāng)假定的正方向是從A指向B時，那么從B指向A就是負(fù)的。這就是為什么我們要標(biāo)記假想的正方向的原因。在圖表中，

43、假定的正方向用箭頭或者下標(biāo)表示，并且作為電壓的正方向。</p><p>　　在電氣工程中應(yīng)用最廣的交流電是——按正弦曲線成周期性變化的交流電；正弦電流通常比非正弦電流的能量損失要小，并且非正弦電流還會感應(yīng)電壓，對通信電路有很大的干擾。</p><p>　　在遠(yuǎn)距離信息傳遞中（電纜或者無線電通信電路，遠(yuǎn)程遙控等）也通常用正弦電，但是用放大器對頻率和性狀進(jìn)行調(diào)整過的，。周期性非正弦電流也可以被

44、認(rèn)為是許多不同頻率的正弦電流的疊加。這就是正弦電流為什么這么重要的原因。</p><p><b>　　交流發(fā)電機(jī)</b></p><p>　　交流發(fā)電機(jī)由定子和轉(zhuǎn)子組成。通常，轉(zhuǎn)子上帶磁極和縈繞線圈。這些發(fā)電機(jī)的線圈，在電機(jī)中建立磁場。它產(chǎn)生出流通與線圈與電刷之間的電流。定子的作用就是固定機(jī)子。定子中線圈都是有序的連接的，就象在圖4.2中用線表示的一樣。</p&

45、gt;<p>　　在導(dǎo)體中感應(yīng)電動勢表示為：</p><p><b>　　表示磁場密度；</b></p><p>　　表示導(dǎo)體的有效長度；</p><p>　　表示磁場與導(dǎo)體之間的相對速度。</p><p>　　當(dāng)和是常量的時候，感應(yīng)電動勢將隨著磁密度的變化而變化。假如感應(yīng)電動勢是正弦型的（通常是很毛躁的）

46、那么在定子周圍的磁通分布就越接近于正弦型。</p><p>　　感應(yīng)電動勢的正負(fù)隨著磁極的改變而改變。假如轉(zhuǎn)子的轉(zhuǎn)速以多少轉(zhuǎn)每分鐘記，感應(yīng)電動勢的頻率就為</p><p>　　因?yàn)轭l率為50Hz,對于一對磁極的發(fā)電機(jī)的轉(zhuǎn)子來說就要每分鐘轉(zhuǎn)3000轉(zhuǎn)。對于兩對磁極的來說，為1500轉(zhuǎn)。因?yàn)樗俣热绱酥?，要承受很大的機(jī)械應(yīng)力，必須把轉(zhuǎn)子做成隱極性的。</p><p>　

47、　高頻率的發(fā)電機(jī)頻率能達(dá)到800到8000Hz，它們必須經(jīng)過特殊的設(shè)計(jì)。它們通常被應(yīng)用在熱處理或者感應(yīng)熱的地方。高頻被應(yīng)用在閥門或半導(dǎo)體震動的場所。</p><p><b>　　正弦電</b></p><p>　　正弦電流的瞬時值可以用下式表示：</p><p>　　這里的Im代表電流的峰值，代表電流的狀態(tài)。值代表時間為0是的最初狀態(tài)。連續(xù)電流

48、的值是隨時間變化的。當(dāng)增長到時，重復(fù)完前一個周期值。因此，通常意義的電流值，是僅指從0到時的值。</p><p>　　在一個周期中要經(jīng)歷從0到的變化。所以，狀態(tài)變化率就表述為。用希臘字母表示，被叫做pulsatance.注意到，我們可以寫作</p><p>　　被描述成弧度每分。因此，因?yàn)橛蓄l率，。以及前面的式子，我們有：</p><p>　　同樣頻率的正弦電流，但

49、是幅度和角度的不同，在前面的式子中有表示。它們的瞬時值為：</p><p>　　時間t或者，對時間的比例，用橫坐標(biāo)表示。</p><p>　　角度通常是在與最初的值的比對中測得的，通常和參考的時間相對應(yīng)，并且在給定的正弦量剛剛過0時（從負(fù)到正）。當(dāng)>0時，正弦電流i 的初值就向左偏移，當(dāng)<0是，初值就相應(yīng)的向右偏移。</p><p>　　對于以上兩者，正

50、弦電流的瞬時值可以用下面的公式表示：</p><p><b>　　)</b></p><p><b>　　這里有。</b></p><p>　　兩個或多個正弦電流隨著初始角度的不同，在圖上將表現(xiàn)出一定量值的偏移。這些形狀的變化，或者叫狀態(tài)位子的移動，由他們各自的零起點(diǎn)標(biāo)記，很顯然與不同的角度對應(yīng)著?？磮D4.3，我們就說電流