外文翻譯---電動機的結(jié)構(gòu)特點

1、<p>　　Construction Features of Electrical Machines</p><p>　　The energy-conversion process usually involves the presence of two important features in a given electromechanical device. These are the field

2、 winding, which produces the flux density, and the armature winding, in which the “working" emf is induced. In this section the salient construction features of the principal types of electric machines are described

3、 to show the location of these windings, as well as to demonstrate the general composition of such machines.</p><p>　　1.Three-Phase Induction Motor</p><p>　　This is one of the most rugged and mo

4、st widely used machines in industry. Its stator is composed of laminations of high-grade sheet steel. The inner surface is slotted to accommodate a three-phase winding. In Fig.5.2 (a) the three-phase winding is represent

5、ed by three coils, the axes of which are 120 electrical degrees apart. Coil aa' represents all the coils assigned to phase a for one pair of poles. Similarly coil bb' represents phase b coils, and coil cc' re

6、presents phase c coils. When one en</p><p>　　The rotor also consists of laminations of slotted ferromagnetic material, but the rotor winding may be either the squirrel-cage type or the wound-rotor type. The

7、latter is of a form similar to that of the stator winding. The winding terminals are brought out to three slip rings. This allows an external three-phase resistor to be connected to the rotor winding for the purpose of p

8、roviding speed control. As a matter of fact, it is the need for speed control which in large measure accounts for the </p><p>　　In normal operation a three-phase voltage is applied to the stator winding at p

9、oints a-b-c in Fig.5.2.Magnetizing currents flow in each phase which together create a revolving magnetic field having two poles. The speed of field is fixed by the frequency of the magnetizing currents and the number of

10、 poles for which the stator winding is designed. Fig.5.2 shows the configuration for two poles. If the pattern a-c'-b-a'-c-b' is made to span only 180 mechanical degrees and then is repeated over the r</p&

11、gt;<p>　　The revolving field produced by stator winding cuts the rotor conductors, thereby inducing voltages. Since the rotor winding is short-circuited by the end rings, the induced voltages cause currents to flo

12、w which in turn react with the field to produce electromagnetic torque—and so motor action results.</p><p>　　Accordingly, on the basis of the foregoing description, it should be clear that for the three-phas

13、e induction motor the field winding is located on the stator and the armature winding on the rotor. Another point worth noting is that this machine is singly excited, i.e., electrical power is applied only to the stator

14、winding. Current flows through the rotor winding by induction. As a consequence both the magnetizing current, which sets up the magnetic field, and the power current which allows ene</p><p>　　2.Synchronous M

15、achines</p><p>　　The essential construction features of the synchronous machine are depicted in Fig.5.3. The stator consists of a stator frame, a slotted stator core, which provides a low-reluctance path for

16、 the magnetic flux, and a three-phase winding imbedded in the slots. Note that the basic two-pole pattern of Fig.5.2 (a) is repeated twice, indicating that the three-phase winding is designed for four poles. The rotor ei

17、ther is cylindrical and equipped with a distributed winding or else has salient poles with</p><p>　　When operated as a generator the synchronous machine receives mechanical energy from a prime mover such as

18、a steam turbine and is driven at some fixed speed. Also, the rotor winding is energized from a DC source, thereby furnishing a field distribution along the air gap. When the rotor is at standstill and DC flows through th

19、e rotor winding, no voltage is induced in the stator winding because the flux is not cutting the stator coils. However, when the rotor is being driven at full speed,voltage </p><p>　　For the synchronous mach

20、ine the field winding is located on the rotor; the armature windings is located on the stator. This statement is valid even when the synchronous machine operates as a motor. In this mode AC power is applied to the stator

21、 winding and DC power is applied to the rotor winding for the purpose of energizing the field poles. Mechanical energy is then taken from the shaft. Note, too, that unlike the induction motor, the synchronous motor is a

22、doubly excited machine; i.e., energy</p><p>　　Because the magnetizing current for the synchronous machine originates from a separate source (the DC supply), the air-gap lengths are larger than those found in

23、 induction motors of comparable size and rating. However, synchronous machines are more expensive and less rugged than induction motors in the smaller horsepower ratings because the rotor must be equipped with slip rings

24、 and brushes in order to allow the direct current to be conducted to the field winding.</p><p>　　3.DC Machines</p><p>　　Electromechanical energy-conversion devices that are characterized by dire

25、ct current are more complicated than the AC type. In addition to a field winding and armature winding, a third component is needed to serve the function of converting the induced AC armature voltage into a DC voltage. Ba

26、sically the device is a mechanical rectifier and is called a commutator.</p><p>　　Appearing in FIg.5.4 are the principal features of the DC machine. The stator consists of an unlaminated ferromagnetic materi

27、al equipped with a protruding structure around which coils are wrapped. The flow of direct current through the coils establishes a magnetic field distribution along the periphery of the air gap in much the same manner as

28、 occurs in the rotor of the synchronous machine. Hence in the DC machine the field winding is located on the stator. It follows then that the armature win</p><p>　　In FIg.5.4 the armature winding is depicte

29、d as a coil wrapped around a toroid. This is merely a schematic convenience. In an actual winding, no conductors are wasted by placing them on the inner surface of the rotor core where no flux penetrates. In the Fig.5.3

30、those parts of the armature winding which lie directly below the brush width are assumed to have the insulation removed, i.e., the copper is exposed. This allows current to be conducted to and from the armature winding t

31、hrough the brush a</p><p>　　For motor action direct current is made to flow through the field winding as well as the armature winding. If current is assumed to flow into brush B1 in Fig.5.4, then mote that o

32、n the left side of the rotor for the outside conductors current flows into the paper while the opposite occurs for the conductors located on the outside surface of the right side of the rotor. A force is produced on each

33、 conductor, thereby producing a torque causing clockwise rotation. Now the function of the commutator</p><p>　　Another point of interest in Fig.5.4 concerns the location of the brushes. By placing the brushe

34、s on a line perpendicular to the field axis all conductors contribute in producing a unidirectional torque. If, on the other hand, the brushes were placed on the same line as the field axis, then half of the conductors w

35、ould produce clockwise torque and the other half of the counterclockwise torque, yield a zero net torque.</p><p>　　摘自《電氣自動化專業(yè)英語》哈工大出版社 李久勝、馬洪飛等編 2000年6月第二版</p><p><b>　　譯文：</b></p

36、><p><b>　　電動機的結(jié)構(gòu)特點</b></p><p>　　機電設(shè)備的能量轉(zhuǎn)換過程通常包括兩個重要的結(jié)構(gòu)特點，他們是產(chǎn)生磁通密度的勵磁繞組和工作被感應(yīng)的電樞繞組。電動機主要類型的顯著結(jié)構(gòu)特點是這些用繞組描述就象電機基本結(jié)構(gòu)所示的那樣。</p><p><b>　　1.三相感應(yīng)電動機</b></p><

37、;p>　　這是一種在工業(yè)上使用最多最廣泛的電機之一，他的定子有高級薄剛片疊壓而成，內(nèi)表面開有容納三相繞組的槽。在圖5.2（a）中三相繞組用三個軸線相隔120電角度線圈表示。線圈aa‘表示一對磁極下指定的相的繞組，同理線圈bb’表示b相繞組，線圈cc‘表示c相繞組，當(dāng)三相末端如圖5.2（b）所示那樣相連，三相定子繞組稱為Y連接。這樣的繞組稱為三相繞組是因為三相中每一相被旋轉(zhuǎn)的磁通密度感應(yīng)的電動勢相差120電角度——三相對稱系統(tǒng)的特點

38、。</p><p>　　轉(zhuǎn)子也是由被開槽的鐵磁材料疊壓而成，但是轉(zhuǎn)子繞組可以是籠型的也可以是繞線型的，而且繞線型和定子繞組相似。繞組終端與三個滑環(huán)相連，這樣使得外部的三相導(dǎo)體和轉(zhuǎn)子相連，輸出轉(zhuǎn)速。在實際情況中，繞線型感應(yīng)電動機在需要高速時使用，否則就用籠型感應(yīng)電動機?；\型繞組是許多銅導(dǎo)條嵌入槽中，兩端用銅端環(huán)連接（有些小型號用鋁），這種籠型結(jié)構(gòu)比繞線型結(jié)構(gòu)不僅更簡單更經(jīng)濟，而且使用也很多，沒有了滑環(huán)和碳刷的麻煩。

39、</p><p>　　正常操作時，三相電動勢如圖5.2所示供給定子繞組的a-b-c點，勵磁電流流過每一相，在兩極的作用下，產(chǎn)生旋轉(zhuǎn)磁場，磁場的轉(zhuǎn)速有勵磁電流的頻率和轉(zhuǎn)子繞組的極數(shù)決定。圖5.2所示結(jié)構(gòu)為雙極。如果a-c’-b-a‘-c-b’僅占180機械角度，并在剩余的180機械角度重復(fù)一次，則該電機有4個極。對于一個p極的電機基本繞組必須在定子內(nèi)表面圓周范圍內(nèi)重復(fù)p/2次。</p><p&g

40、t;　　定子繞組產(chǎn)生的旋轉(zhuǎn)磁場切割轉(zhuǎn)子導(dǎo)體產(chǎn)生感應(yīng)電動勢。由于轉(zhuǎn)子繞組通過端環(huán)短路，則感應(yīng)電動機形成（轉(zhuǎn)子）電流，電流與磁場相互作用產(chǎn)生電磁轉(zhuǎn)矩，結(jié)果使得電動機運動起來。</p><p>　　因此，在前面描述的基礎(chǔ)上，我們知道對于三相感應(yīng)電動機磁場繞組位于定子而電樞繞組位于轉(zhuǎn)子上。另一點需要注意的是這種電動機單獨激勵，即電源只供電給定子繞組，電流流過被感應(yīng)的轉(zhuǎn)子繞組。結(jié)果，由勵磁磁場產(chǎn)生的勵磁電流和能量傳遞到軸上

41、負載的電源電流都流過定子繞組。由于這個原因，保持勵磁電流盡可能的小是為了使電路元件可以有相應(yīng)大的電流，感應(yīng)電動機的氣隙也是盡可能的小。氣隙長度從小電機的0.02英寸到高速高效的0.05英寸改變形式。</p><p><b>　　2.同步電機</b></p><p>　　同步電機的基本結(jié)構(gòu)特點如圖5.3所示。定子由給定磁路的機殼、開槽的定子鐵心和三相嵌入槽內(nèi)的繞組組成。

42、圖5.2（a）為基本的雙極形式重復(fù)兩次，三相繞組表示為四個磁極。轉(zhuǎn)子或者是配備了分布式繞組的圓柱式或者是如圖5.3所示的每個支柱上有線圈繞組的凸極式。圓柱式的結(jié)構(gòu)常用于高速發(fā)電機，另一方面，凸極式結(jié)構(gòu)常用于轉(zhuǎn)速至少為1800轉(zhuǎn)每分的同步電動機。</p><p>　　當(dāng)同步電機按照發(fā)電機運行時，他就象從水蒸氣渦輪機那收到機械能，并且是恒定的轉(zhuǎn)速。而且，轉(zhuǎn)子繞組被直流電源所激勵，因此設(shè)備的磁極沿著氣隙分布。當(dāng)轉(zhuǎn)子停止

43、，直流通過轉(zhuǎn)子繞組，沒有感應(yīng)電動勢產(chǎn)生，這是因為磁場沒有切割定子繞組。然而，當(dāng)轉(zhuǎn)子額定轉(zhuǎn)速運行時，定子繞組中產(chǎn)生感應(yīng)電動勢，加上適當(dāng)?shù)呢撦d，電能就被傳送出去了。</p><p>　　由于同步電機的磁場繞組置于轉(zhuǎn)子上，電樞繞組置于定子上，當(dāng)同步電機作為電動機使用時，交流電源接定子繞組而直流電源接轉(zhuǎn)子繞組，采用這種方式為了磁極激勵，使機械能從軸上傳送。不同于感應(yīng)電動機的是同步電動機是雙重激發(fā)的電機，即能量不僅供給定子

44、也供給轉(zhuǎn)子。實際上，正式由于他這種僅僅一種速度產(chǎn)生非零轉(zhuǎn)矩的特征而得名同步的。</p><p>　　因為同步電動機的勵磁電流來自單獨的電源（直流電源），氣隙長度比同規(guī)格的感應(yīng)電動機長，然而，同步電動機在小功率卻比感應(yīng)電動機貴，由于轉(zhuǎn)子必須配備滑環(huán)和電刷來處理磁場繞組的直流電流，故使用較少。</p><p><b>　　3.直流電機</b></p><

45、;p>　　直流電機的能量轉(zhuǎn)換裝置比交流設(shè)備更復(fù)雜。除了勵磁繞組和電樞繞組之外，第三個就是用來認為轉(zhuǎn)換交流電動勢為直流電動勢的裝置。通常是一個機械整流器，也叫換向器。</p><p>　　圖5.4描述了直流電動機的主要的特征。定子由非疊層的鐵磁設(shè)備組成，線圈環(huán)繞在他突出的結(jié)構(gòu)上。流過繞組的直流電流建立了分布在氣隙圓周的磁場，同步電動機的轉(zhuǎn)子也采用這種方式。因此，在直流電動機的勵磁繞組位于定子上。電樞繞組位于轉(zhuǎn)

46、子上。轉(zhuǎn)子由疊制的鐵心組成，在鐵心上開有容納電樞繞組的槽，他也可以容納換向器—一系列銅片分割后整理成圓柱式。在換向器上適當(dāng)位置放置碳刷，其作用是當(dāng)電機作為電動機或發(fā)電機運行時，使直流電流流入或流出電樞繞組。</p><p>　　在圖5.4中，電樞繞組環(huán)繞在環(huán)狀物上，這僅僅是大概。而實際繞組，沒有磁通通過的轉(zhuǎn)子鐵心內(nèi)表面不放置導(dǎo)體。在圖5.3中，那些位于電刷寬度下面的電樞繞組部分，銅片是暴露的。這使得電流在電機旋轉(zhuǎn)

47、時能夠?qū)腚姌欣@組。在實際繞組中，通過把線圈和換向片相連并把電刷放在換向器上，使得每個線圈與電刷都是連接。</p><p>　　電動機直流電流流過勵磁繞組就象流過電樞繞組。如圖5.4所示，如果假定電流由電刷B1流入，則應(yīng)注意的是轉(zhuǎn)子左側(cè)的外部導(dǎo)體電流是流入紙面的，而位于轉(zhuǎn)子右側(cè)的外部導(dǎo)體電流方向是相反的。每個導(dǎo)體產(chǎn)生力，因此產(chǎn)生瞬時針方向的轉(zhuǎn)矩。現(xiàn)在，換向器的作用就是保證當(dāng)圖5.4所示的導(dǎo)體由電刷B1的左側(cè)旋轉(zhuǎn)至

48、右側(cè)時，電流方向也隨之改變，這樣對整個電樞繞組來說，就可以產(chǎn)生一個不變的連續(xù)的轉(zhuǎn)矩?；叵敕聪虻膶?dǎo)體電流在相反極性的勵磁磁場中，轉(zhuǎn)矩不變。無論電樞是否旋轉(zhuǎn)，由于換向器使電流總是以同樣的方向流入電樞繞組兩側(cè)，則電流相反。</p><p>　　另外，在圖5.4中涉及電刷的位置。在放置電刷在垂直的磁場軸線上，所有的導(dǎo)體產(chǎn)生不變的轉(zhuǎn)矩。另一方面，如果電刷與磁場的軸線放在同一條線上，則一半的導(dǎo)體產(chǎn)生順時針方向的轉(zhuǎn)矩，另一半的