直流電機(jī)的介紹_外文翻譯

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直流電機(jī)的特點(diǎn)是他們的多功用性。依靠不同的并勵(lì)、串勵(lì)和他勵(lì)勵(lì)磁繞組的組合，他們可以被設(shè)計(jì)為動(dòng)態(tài)的和靜態(tài)的運(yùn)轉(zhuǎn)方式從而呈現(xiàn)出寬廣范圍變化的伏安特性或速度轉(zhuǎn)矩特性。因?yàn)樗?jiǎn)單的可操縱性，直流系統(tǒng)經(jīng)常被用于需要大范圍發(fā)動(dòng)機(jī)轉(zhuǎn)速或精確控制發(fā)動(dòng)機(jī)的輸出量的場(chǎng)合。
　　　
直流電機(jī)的總貌如圖所示。定子上有凸極，而且由一個(gè)或幾個(gè)勵(lì)磁線圈勵(lì)磁。氣隙磁通量以磁極中心線為軸線對(duì)稱(chēng)分布。這條軸線叫做磁場(chǎng)軸線或直軸。
　　　
我們都知道，在每個(gè)旋轉(zhuǎn)電樞線圈中產(chǎn)生的交流電壓，經(jīng)由一與電樞聯(lián)接的旋轉(zhuǎn)的換向器和靜止的電刷，在電樞線圈出線端轉(zhuǎn)換成直流電壓。換向器－電刷組合構(gòu)成了一個(gè)機(jī)械整流器，它形成了一個(gè)直流電樞電壓和一個(gè)被固定在空間中的電樞磁勢(shì)波形。電刷的位置應(yīng)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(shì)波的軸線與磁極軸線相差90度,也就是在交軸上。在示意圖中，電刷位于交軸上，因?yàn)檫@是線圈和電刷相連的位置。這樣，電樞磁勢(shì)波的軸線也是沿著電刷軸線的（在實(shí)際電機(jī)中，電刷的幾何位置大約偏移圖例中所示位置90度，這是因?yàn)樵哪┒诵螤顦?gòu)成圖示結(jié)果與換向器相連）。電刷上的電磁轉(zhuǎn)矩和旋轉(zhuǎn)電勢(shì)與磁通分布的空間波形無(wú)關(guān)；為了方便我們可以假設(shè)在氣隙中有一個(gè)正弦的磁通密度波形。轉(zhuǎn)矩可以從磁場(chǎng)的觀點(diǎn)分析得到。
　　　
轉(zhuǎn)矩可以用每個(gè)磁極的直軸氣隙磁通和電樞磁勢(shì)波的空間基波分量相互作用的結(jié)果來(lái)表示。在交軸上的電刷和這個(gè)磁場(chǎng)的夾角為90度，其正弦值等于1，對(duì)于一臺(tái)極電機(jī)


D.C. machines are characterized by their versatility. By means of various combinations of shunt-, series-, and separately excited field windings they can be designed to display a wide variety of volt-ampere or speed-torque characteristics for both dynamic and steady state operation. Because of the ease with which they can be controlled, systems of D.C. machines are often used in applications requiring a wide range of motor speeds or precise control of motor output.
　　　
The essential features of a D.C. machine are shown schematically. The stator has salient poles and is excited by one or more field coils. The air-gap flux distribution created by the field winding is symmetrical about the centerline of the field poles. This is called the field axis or direct axis.
　　　
As we know, the A.C. voltage generated in each rotating armature coil is converted to D.C. 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 forms a mechanical rectifier, resulting in a D.C. armature voltage as well as an armature m.m.f. Wave then is 90 electrical degrees from the axis of the field poles, i.e. in the quadrature axis. In the schematic representation the brushes are shown in quadrature axis because this is the position of the coils to which they are connected. The armature m.m.f. Wave then is along the brush axis as shown. (The geometrical position of the brushes in an actual machine is approximately 90 electrical degrees from their position in the schematic diagram because of the shape of the end connections to the commutator.)
　　　
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 assume a sinusoidal flux-density wave in the air gap. The torque can then be found from the magnetic field viewpoint.

The torque can be expressed in terms of the interaction of the direct-axis air-gap flux per pole and 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 pole machine