電氣畢業(yè)設(shè)計用外文翻譯（中英文對照）--負載運行的變壓器及直流電機導論

1、<p><b>　　中文5580字</b></p><p>　　The Transformer on load﹠Introduction to DC Machines</p><p>　　The Transformer on load</p><p>　　It has been shown that a primary input v

2、oltage can be 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 conside

3、red. The secondary 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 ca

4、use an appreciable 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

5、back e.m.f.,（）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

6、not be met without 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 fl

7、ux are increased 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

8、virtually the 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 po

9、ints should be 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 ,

10、 if the horizontal 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

11、 flux is zero, 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 b

12、y the addition 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 purp

13、oses of electrically 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

14、 terms of the 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 proporti

15、onal to turns, 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 bec

16、omes , and secondary 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 ca

17、lled referring 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 w

18、inding must be 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 en

19、ergy in the leakage 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 se

20、condary winding 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 d

21、ifference in secondary 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,

22、 but it is sometimes 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. ,; si

23、milarly and .</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 termin

24、als to return 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 behav

25、iour detected 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, bu

26、t a few anomalies 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 . Slig

27、htly different 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 </

28、b></p><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 o

29、f change of voltage 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 ev

30、en for power frequencies .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 s

31、ink but the referred 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 t

32、his representation 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

33、could be referred to the secondary winding and this may save calculation time .</p><p>　　The resistances and reactances can be obtained from two simple light load tests.</p><p>　　Introduction to

34、 DC Machines</p><p>　　DC machines are characterized by their versatility. By means of various combination of shunt, series, and separately excited field windings they can be designed to display a wide variet

35、y of volt-ampere or speed-torque characteristics for both dynamic and steadystate operation. Because of the ease with which they can be controlled , systems of DC machines are often used in applications requiring a wide

36、range of motor speeds or precise control of motor output.</p><p>　　The essential features of a DC machine are shown schematically. The stator has salient poles and is excited by one or more field coils. The

37、air-gap flux distribution created by the field winding is symmetrical about the centerline of the field poles. This axis is called the field axis or direct axis.</p><p>　　As we know , the AC voltage generate

38、d in each rotating armature coil is converted to DC in the external armature terminals by means of a rotating commutator and stationary brushes to which the armature leads are connected. The commutator-brush combination

39、forms a mechanical rectifier, resulting in a DC armature voltage as well as an armature m.m.f. wave which is fixed in space. The brushes are located so that commutation occurs when the coil sides are in the neutral zone

40、, midway between the fie</p><p>　　The magnetic torque and the speed voltage appearing at the brushes are independent of the spatial waveform of the flux distribution; for convenience we shall continue to ass

41、ume a sinusoidal flux-density wave in the air gap. The torque can then be found from the magnetic field viewpoint. </p><p>　　The torque can be expressed in terms of the interaction of the direct-axis air-gap

42、 flux per pole and the space-fundamental component of the armature m.m.f. wave . With the brushes in the quadrature axis, the angle between these fields is 90 electrical degrees, and its sine equals unity. For a P pole

43、 machine</p><p>　　In which the minus sign has been dropped because the positive direction of the torque can be determined from physical reasoning. The space fundamental of the sawtooth armature m.m.f. wave

44、is 8/ times its peak. Substitution in above equation then gives </p><p>　　Where =current in external armature circuit;</p><p>　　=total number of conductors in armature winding;</p><p&

45、gt;　　=number of parallel paths through winding;</p><p><b>　　And </b></p><p>　　Is a constant fixed by the design of the winding.</p><p>　　The rectified voltage generated

46、in the armature has already been discussed before for an elementary single-coil armature. The effect of distributing the winding in several slots is shown in figure ,in which each of the rectified sine waves is the volta

47、ge generated in one of the coils, commutation taking place at the moment when the coil sides are in the neutral zone. The generated voltage as observed from the brushes is the sum of the rectified voltages of all the coi

48、ls in series between brushes</p><p>　　Where is the design constant. The rectified voltage of a distributed winding has the same average value as that of a concentrated coil. The difference is that the rippl

49、e is greatly reduced. </p><p>　　From the above equations, with all variable expressed in SI units:</p><p>　　This equation simply says that the instantaneous electric power associated with the sp

50、eed voltage equals the instantaneous mechanical power associated with the magnetic torque , the direction of power flow being determined by whether the machine is acting as a motor or generator.</p><p>　　The

51、 direct-axis air-gap flux is produced by the combined m.m.f. of the field windings, the flux-m.m.f. characteristic being the magnetization curve for the particular iron geometry of the machine. In the magnetization curv

52、e, it is assumed that the armature m.m.f. wave is perpendicular to the field axis. It will be necessary to reexamine this assumption later in this chapter, where the effects of saturation are investigated more thoroughly

53、. Because the armature e.m.f. is proportional to flux tim</p><p>　　Figure shows the magnetization curve with only one field winding excited. This curve can easily be obtained by test methods, no knowledge of

54、 any design details being required.</p><p>　　Over a fairly wide range of excitation the reluctance of the iron is negligible compared with that of the air gap. In this region the flux is linearly proportiona

55、l to the total m.m.f. of the field windings, the constant of proportionality being the direct-axis air-gap permeance.</p><p>　　The outstanding advantages of DC machines arise from the wide variety of operati

56、ng characteristics which can be obtained by selection of the method of excitation of the field windings. The field windings may be separately excited from an external DC source, or they may be self-excited; i.e., the mac

57、hine may supply its own excitation. The method of excitation profoundly influences not only the steady-state characteristics, but also the dynamic behavior of the machine in control systems.</p><p>　　The con

58、nection diagram of a separately excited generator is given. The required field current is a very small fraction of the rated armature current. A small amount of power in the field circuit may control a relatively large a

59、mount of power in the armature circuit; i.e., the generator is a power amplifier. Separately excited generators are often used in feedback control systems when control of the armature voltage over a wide range is require

60、d. The field windings of self-excited generators may </p><p>　　In the typical steady-state volt-ampere characteristics, constant-speed prime movers being assumed. The relation between the steady-state genera

61、ted e.m.f. and the terminal voltage is </p><p>　　Where is the armature current output and is the armature circuit resistance. In a generator, is large than ; and the electromagnetic torque T is a counter

62、torque opposing rotation.</p><p>　　The terminal voltage of a separately excited generator decreases slightly with increase in the load current, principally because of the voltage drop in the armature resista

63、nce. The field current of a series generator is the same as the load current, so that the air-gap flux and hence the voltage vary widely with load. As a consequence, series generators are not often used. The voltage of s

64、hunt generators drops off somewhat with load. Compound generators are normally connected so that the m.m.f. </p><p>　　Where is now the armature current input. The generated e.m.f. is now smaller than the

65、terminal voltage , the armature current is in the opposite direction to that in a motor, and the electromagnetic torque is in the direction to sustain rotation of the armature.</p><p>　　In shunt and separate

66、ly excited motors the field flux is nearly constant. Consequently, increased torque must be accompanied by a very nearly proportional increase in armature current and hence by a small decrease in counter e.m.f. to allow

67、this increased current through the small armature resistance. Since counter e.m.f. is determined by flux and speed, the speed must drop slightly. Like the squirrel-cage induction motor ,the shunt motor is substantially a

68、 constant-speed motor having about 5 pe</p><p>　　An outstanding advantage of the shunt motor is ease of speed control. With a rheostat in the shunt-field circuit, the field current and flux per pole can be v

69、aried at will, and variation of flux causes the inverse variation of speed to maintain counter e.m.f. approximately equal to the impressed terminal voltage. A maximum speed range of about 4 or 5 to 1 can be obtained by t

70、his method, the limitation again being commutating conditions. By variation of the impressed armature voltage, very wide s</p><p>　　In the series motor, increase in load is accompanied by increase in the arm

71、ature current and m.m.f. and the stator field flux (provided the iron is not completely saturated). Because flux increases with load, speed must drop in order to maintain the balance between impressed voltage and counter

72、 e.m.f.; moreover, the increase in armature current caused by increased torque is smaller than in the shunt motor because of the increased flux. The series motor is therefore a varying-speed motor with a m</p><

73、;p>　　In the compound motor the series field may be connected either cumulatively, so that its.m.m.f.adds to that of the shunt field, or differentially, so that it opposes. The differential connection is very rarely us

74、ed. A cumulatively compounded motor has speed-load characteristic intermediate between those of a shunt and a series motor, the drop of speed with load depending on the relative number of ampere-turns in the shunt and se

75、ries fields. It does not have the disadvantage of very high light-lo</p><p>　　The application advantages of DC machines lie in the variety of performance characteristics offered by the possibilities of shun

76、t, series, and compound excitation. Some of these characteristics have been touched upon briefly in this article. Still greater possibilities exist if additional sets of brushes are added so that other voltages can be ob

77、tained from the commutator. Thus the versatility of DC machine systems and their adaptability to control, both manual and automatic, are their outstand</p><p>　　負載運行的變壓器及直流電機導論</p><p><b>　

78、　負載運行的變壓器</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。可用于產(chǎn)生負載電流，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。現(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，有一種對鐵芯產(chǎn)生去磁、減小和的趨向。因為一次側(cè)漏阻抗壓降如此之小，所以的微小變化都將導致一次側(cè)電流增加很大，從增大至一個新值。增加的一次側(cè)電流和磁勢近

79、似平衡了全部二次側(cè)磁勢。這樣的話，互感磁通只經(jīng)歷很小的變化，并且實際上只需要與空載時相同的凈磁勢。一次側(cè)總磁勢增加了，它是平衡同量的二次側(cè)磁勢所必需的。在向量方程中，，上式也可變換成。滿載時，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，這是因為總反電動勢仍然與相等且反

80、向。然而此時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勢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）的建立而被進一步削弱。盡管圖中和是分開表示的，但它們在鐵芯中是一個合成量，該合成量在圖示中的瞬時是向下的。這樣，二次側(cè)端電壓降至，它可被看成兩個分量，即，或者向量形式。與一次側(cè)漏磁通一樣，的作用也用一個大體為常數(shù)

81、的漏電感來表征。要注意的是，由于它對互感磁通的作用，一次側(cè)漏磁通對于二次側(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，對的去磁作用引起了一次側(cè)的變化，從而導致了一次側(cè)漏磁通的產(chǎn)生。</p><p>　　如果我們討論一個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增加，從而使得二次側(cè)端電壓隨負載增加而升高。在空載情形下，如果忽略電阻，幅值大小不變，因為它仍提供一個等于的反總電動勢。盡管現(xiàn)在是一次側(cè)和

82、二次側(cè)磁勢的共同作用產(chǎn)生的，但它實際上與相同?；ジ写磐ū仨毴噪S負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，還應得出兩點：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，那么向量圖是以為零時間參數(shù)的，圖中各物理量時間方向并不是該瞬時的。在周期性交變中，有一次側(cè)漏磁通為零的瞬時，也有二次側(cè)

83、漏磁通為零的瞬時，還有它們處于同一方向的瞬時。</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展成二次側(cè)負載時的等效電路。</p><p>　　實際中所有的變壓器的匝數(shù)比都不等于1，盡管有時使其為1也是為了使一個電路與另一個在相同電壓下運行的電路實現(xiàn)電氣隔離。為了分析時的情況，二次側(cè)的反應得從一次側(cè)來看，這種反應只有通過由二次側(cè)的磁勢產(chǎn)

84、生磁場力來反應。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>　　當變換成，由于電動勢與匝數(shù)成正比，所以，與相等。</p><p>　　對于電流，由于對一次側(cè)作用的安匝數(shù)必須保持不變，因此，即。</p><p>　　對于阻抗，由于二次側(cè)電壓變成，電流變?yōu)椋?/p>

85、因此阻抗值，包括負載阻抗必然變?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，而事實上確實簡化成了。</p>&l

86、t;p>　　類似地，與成比例的漏磁場的磁場儲能，求出后驗證與成正比。折算后的二次側(cè)。</p><p>　　盡管看起來似乎不可理解，事實上這種論點是可靠的。實際上，如果我們將實際的二次繞組當真從鐵芯上移開，并用一個參數(shù)設(shè)計成，，，的等效繞組和負載電路替換，在正常電網(wǎng)頻率運行時，從一次側(cè)兩端無法判斷二次側(cè)的磁勢、所需容量及銅耗與前有何差別。</p><p>　　在選擇折算基準時，無非是將

87、一次側(cè)與折算后的二次側(cè)匝數(shù)設(shè)為相等，除此之外再沒有什么更要緊的了。但有時將一次側(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“1”的量都變換成了下標“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，對于一臺實際的變壓器，，；同樣地，。</p><p>　　的通常情形時的等效電路，它除了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。在運用這種理想轉(zhuǎn)

88、換之前，內(nèi)部電壓和功率損耗已進行了計算。當在電路中選擇了適當?shù)膮?shù)時，在一、二次側(cè)兩端測得的變壓器運行情況與在該電路相應端所測得的請況是完全一致的。將線圈和線圈并排放置在一個鐵芯的兩邊，這一點與實際情況之間的差別僅僅是為了方便。當然，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)象又會發(fā)生。例如，流過一次側(cè)阻抗的電流不再是整個一

89、次側(cè)電流。由于通常只是的很小一部分，所有誤差相當小。對一個具體問題可否允許有細微差別的回答取決于是否允許這種誤差的存在。對于這種簡化電路，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)頻率下的正常運行；一旦電壓變化率產(chǎn)生相當大的電容電流時必須考慮電容效應。這對于高電壓和頻率超過100Hz的情形是很重要的。其次，即使是對于電網(wǎng)頻率也并非唯一可行的等效電路。另

90、一種形式是將變壓器看成一個三端或四端網(wǎng)絡(luò)，這樣便產(chǎn)生一個準確的表達，它對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)的電路會擁有一個既產(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)類似飽和效應等現(xiàn)象。</p><p>　　等效電路有兩個入端口形式：</p><p>　　從一次側(cè)看為一個U形電路，其折合后的

91、負載阻抗的端電壓為；</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。在這種電路中有時可省略激磁支路，這樣電路簡化為一臺產(chǎn)生恒值電壓（實際上等于）并帶有阻抗（實際上等于）的發(fā)電機。</p><p>　　在上述兩種情況下，參數(shù)都可折算到二次繞組，這樣可減小計算時間。</p><p>　　其電阻和電抗值可通過兩種簡單的輕載試驗獲得。</p&

92、gt;<p><b>　　直流電機導論</b></p><p>　　直流電機以其多功用性而形成了鮮明的特征。通過并勵、串勵和特勵繞組的各種不同組合，直流電機可設(shè)計成在動態(tài)和穩(wěn)態(tài)運行時呈現(xiàn)出寬廣范圍變化的伏-安或速度-轉(zhuǎn)矩特性。由于直流電機易于控制，因此該系統(tǒng)用于要求電動機轉(zhuǎn)速變化范圍寬或能精確控制電機輸出的場合。</p><p>　　定子上有凸極，由一個

93、或一個以上勵磁線圈勵磁。勵磁繞組產(chǎn)生的氣隙通以磁極中心線為軸線對稱分布，這條軸線稱為磁場軸線或直軸。</p><p>　　我們知道，每個旋轉(zhuǎn)的電樞繞組中產(chǎn)生的交流電壓，經(jīng)由一與電樞連接的旋轉(zhuǎn)的換向器和靜止的電刷，在電樞繞組出線端轉(zhuǎn)換成直流電壓。換向器一電刷的組合構(gòu)成機械整流器，它產(chǎn)生一直流電樞電壓和一在空間固定的電樞磁勢波形。電刷的放置應使換向線圈也處于磁極中性區(qū)，即兩磁極之間。這樣，電樞磁勢波形的軸線與磁極軸線

94、相差90°電角度，即位于交軸上。在示意圖中，電刷位于交軸上，因為此處正是與其相連的線圈的位置。這樣，如圖所示電樞磁勢波的軸線也是沿著電刷軸線的。（在實際電機中，電刷的幾何位置大約偏移圖例中所示位置90°電角度，這是因為元件的末端形狀構(gòu)成圖示結(jié)果與換向器相連。）</p><p>　　電刷上的電磁轉(zhuǎn)矩和速度電壓與磁通分布的空間波形無關(guān)；為了方便起見，我們假設(shè)氣隙中仍然是正弦磁密波，這樣便可以從磁場

95、分析著手求得轉(zhuǎn)矩。</p><p>　　轉(zhuǎn)矩可以用直軸每極氣隙磁通和電樞磁勢波的空間基波分量相互作用的結(jié)果來表示。電刷處于交軸時，磁場間的角度為90°電角度，其正弦值等于1，則對于一臺P極電機</p><p>　　式中由于轉(zhuǎn)矩的正方向可以根據(jù)物理概念的推斷確定，因此負號已經(jīng)去掉。電樞磁勢鋸齒波的空間基波是峰值的8/。上式變換后有</p><p>　　式中

96、 =電樞外部電路中的電流；</p><p>　　=電樞繞組中的總導體數(shù)；</p><p>　　=通過繞組的并聯(lián)支路數(shù)；</p><p><b>　　且</b></p><p>　　其為一個由繞組設(shè)計而確定的常數(shù)。</p><p>　　簡單的單個線圈的電樞中的整流電壓前面已經(jīng)討論過了。將繞組分散在幾

97、個槽中的效果可用圖形表示，圖中每一條整流的正弦波形是一個線圈產(chǎn)生的電壓，換向線圈邊處于磁中性區(qū)。從電刷端觀察到的電壓是電刷間所有串聯(lián)線圈中整流電壓的總和，在圖中由標以的波線表示。當每極有十幾個換向器片，波線的波動變得非常小，從電刷端觀察到的平均電壓等于線圈整流電壓平均值之和。電刷間的整流電壓即速度電壓，為</p><p>　　式中為設(shè)計常數(shù)。分布繞組的整流電壓與集中線圈有著相同的平均值，其差別只是分布繞組的波形脈

98、動大大減小。</p><p>　　將上述幾式中的所有變量用SI單位制表達，有</p><p>　　這個等式簡單地說明與速度電壓有關(guān)的瞬時功率等于與磁場轉(zhuǎn)矩有關(guān)的瞬時機械功率，能量的流向取決于這臺電機是電動機還是發(fā)電機。</p><p>　　直軸氣隙通由勵磁繞組的合成磁勢產(chǎn)生，其磁通-磁勢曲線就是電機的具體鐵磁材料的幾何尺寸決定的磁化曲線。在磁化曲線中，因為電樞磁勢波

99、的軸線與磁場軸線垂直，因此假定電樞磁勢對直軸磁通不產(chǎn)生作用。這種假設(shè)有必要在后述部分加以驗證，屆時飽和效應會深入研究。因為電樞電勢與磁通成正比，所以通常用恒定轉(zhuǎn)速下的電樞電勢來表示磁化曲線更為方便。任意轉(zhuǎn)速時，任一給定磁通下的電壓與轉(zhuǎn)速成正比，即</p><p>　　圖中表示只有一個勵磁繞組的磁化曲線，這條曲線可以很容易通過實驗方法得到，不需要任何設(shè)計步驟的知識。</p><p>　　在一