【正文】 便的。對(duì)一個(gè)具體問(wèn)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。當(dāng)然，就變壓器本身來(lái)說(shuō)，兩線圈是 繞在同一鐵芯柱上的。2V 折算回 2V 而在二次側(cè)兩端引入了一理想的無(wú)損耗轉(zhuǎn)換外，其他方面是一樣的。 XX ? ；同樣地 139。 17 在選擇折算基準(zhǔn)時(shí)，無(wú)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。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(kāi)，并用一個(gè)參數(shù)設(shè)計(jì)成 1N ， 39。折算后的二次側(cè) 2212221222 )/()/(39。 222RI 必須等于 22RI ，而）222122122 /()/( NNRNNI ?? 事實(shí)上確實(shí)簡(jiǎn)化成了 222RI 。 我們可以用一些方法來(lái)驗(yàn)證上述折算過(guò)程是否正確。因此，22212 )/(39。 NININI ?? ，即 2122 )/( INNI ? 。 ENNE ? ，與 1E 相等。為了分析 21 NN ? 時(shí)的16 情況，二次側(cè)的反應(yīng)得從一次側(cè)來(lái)看，這種反應(yīng)只有通過(guò)由二次側(cè)的磁勢(shì)產(chǎn)生磁場(chǎng)力來(lái)反應(yīng)。其次，如果橫軸像通常取的話，那么向量圖是以 0??m 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?；ジ写磐ū仨毴噪S負(fù)載變化而變化以改變 1E ，從而產(chǎn)生更大的一次側(cè)電流。這兩種漏磁通，緊密相關(guān)；例如，2? 對(duì) m? 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。盡管圖中 m? 和 2? 是分開(kāi)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)是向下的。交鏈一次繞組的總磁通 111 ??????? mp 沒(méi)有變化，這是因?yàn)榭偡措妱?dòng)勢(shì) dtdNE /111 ??仍然與 1V 相等且反向。在向量方程中， 102211 NININI ?? ，上式也可變換成221011 NININI ?? 。因?yàn)橐淮蝹?cè)漏阻抗壓降如此之小，所以 1E 的微小變化都將導(dǎo)致一次側(cè)電流增加很大，從 0I 增大至一個(gè)新值 ? ? ? ?ijXREVI ??? 1111 / 。 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 varyingspeed motor with a markedly drooping speedload characteristic. For applications requiring heavy torque overloads, this characteristic is particularly advantageous because the corresponding power overloads are held to more reasonable values by the associated speed drops. Very favorable starting characteristics also result from the increase in flux with increased armature current. In the pound motor the series field may be connected either cumulatively, so that to that of the shunt field, or differentially, so that it opposes. The differential connection is very rarely used. A cumulatively pounded motor has speedload characteristic intermediate between those of a shunt and a series motor, the drop of speed with load depending on the relative number of ampereturns in the shunt and series fields. It does not have the disadvantage of very high lightload speed associated with a series motor, but it retains to a considerable degree the advantages of series excitation. The application advantages of DC machines lie in the variety of performance characteristics offered by the possibilities of shunt, series, and pound 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 obtained from the mutator. Thus the versatility of DC machine systems and their adaptability to control, both manual and automatic, are their outstanding features. 14 負(fù)載運(yùn)行的變壓器及直流電機(jī)導(dǎo)論 負(fù)載運(yùn)行的變壓器 通過(guò)選擇合適的匝數(shù)比，一次側(cè)輸入電壓 1V 可任意轉(zhuǎn)換成所希望的二次側(cè)開(kāi)路電壓 2E 。 And mPCK aa ?2? Is a constant fixed by the design of the winding. The rectified voltage generated in the armature has already been discussed before for an elementary singlecoil armature. The effect of distributing the winding in several slots is shown in figure, in which each of the rectified sine waves is the 9 voltage generated in one of the coils, mutation 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 coils in series between brushes and is shown by the rippling line labeled ae in figure. With a dozen or so mutator segments per pole, the ripple bees very small and the average generated voltage observed from the brushes equals the sum of the average values of the rectified coil voltages. The rectified voltage ae between brushes, known also as the speed voltage, is mdamdaa WKWmPCe ??? ?? 2 Where aK 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 ripple is greatly reduced. From the above equations, with all variable expressed in SI units: maa Twie ? This equation simply says that the instantaneous electric power associated with the speed voltage equals the instantaneous mechanical power associated with the magic torque, the direction of power flow being determined by whether the machine is acting as a motor or generator. The directaxis airgap flux is produced by the bined . ffiN? of the field windings, the . characteristic being the magization curve for the particular iron geometry of the machine. In the magization curve, it is assumed that the armature . 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. Because the armature . is proportional to flux 10 times speed, it is usually more convenient to express the magization curve in terms of the armature . 0ae at a constant speed 0mw . The voltage ae for a given flux at any other speed mw is proportional to the speed,. 00 amma ewwe ? Figure shows the magization curve with only one field winding excited. This curve can easily be obtained by test methods, no knowledge of any design details being required. Over a fairly wide range of excitation the reluctance of the iron is negligible pared with that of the air gap. In this region the flux is linearly proportional to the total . of the field windings, the constant of proportionality being the directaxis airgap permeance. The outstanding advantages of DC machines arise from the wide variety of operating 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 selfexcited。2V ,or (b) Viewed from the secondary as a source of constant voltage 1V with internal drops due to 1Re and 1Xe . The magizing branch is sometimes omitted in this representation and so the circuit