【正文】 the mutual flux. The two leakage fluxes are closely related。And 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 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 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 between brushes, known also as the speed voltage, is 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 ripple is greatly reduced. From the above equations, with all variable expressed in SI units: This equation simply says that the instantaneous electric power associated with the speed 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.The directaxis airgap flux is produced by the bined . of the field windings, the . characteristic being the magnetization curve for the particular iron geometry of the machine. In the magnetization 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 times speed, it is usually more convenient to express the magnetization curve in terms of the armature . at a constant speed. The voltage for a given flux at any other speed is proportional to the speed,. Figure shows the magnetization 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。因為一次側漏阻抗壓降如此之小，所以的微小變化都將導致一次側電流增加很大，從增大至一個新值。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向。這兩種漏磁通，緊密相關；例如，對的去磁作用引起了一次側的變化，從而導致了一次側漏磁通的產(chǎn)生。在周期性交變中，有一次側漏磁通為零的瞬時，也有二次側漏磁通為零的瞬時，還有它們處于同一方向的瞬時。對于阻抗，由于二次側電壓變成，電流變?yōu)?，因此阻抗值，包括負載阻抗必然變?yōu)?。盡管看起來似乎不可理解，事實上這種論點是可靠的。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。其次，即使是對于電網(wǎng)頻率也并非唯一可行的等效電路。直流電機導論直流電機以其多功用性而形成了鮮明的特征。這樣，電樞磁勢波形的軸線與磁極軸線相差90176。電刷處于交軸時，磁場間的角度為90176。電刷間的整流電壓即速度電壓，為 式中為設計常數(shù)。在一個相當寬的勵磁范圍內，鐵磁材料部分的磁阻與氣隙磁阻相比可以忽略不計，在此范圍內磁通與勵磁繞組總磁勢呈線性比例，比例常數(shù)便是直軸氣隙磁導率。勵磁繞組可以與電樞串聯(lián)起來，這便形成了串勵發(fā)電機；勵磁繞組可以與電樞并聯(lián)在一起，這便形成了并勵發(fā)電機；或者勵磁繞組分成兩部分，其中一部分與電樞串聯(lián)，另一部分與電樞并聯(lián)，這便形成復勵發(fā)電機。通常，并勵繞組匝數(shù)多，導線細；而繞在外部的串勵繞組由于它必須承載電機的整個電樞電流，所以其構成的導線相對較粗。與鼠籠式感應電動機相類似，并勵電動機實際上是一種從空載到滿載速降僅約為5%的恒速電動機。因此串勵電動機是一種具有明顯下降的轉速負載特性的變速電動機。其中有一些特性在本文中已大致提及。差復勵連接很少使用。通過這種方法得到最大調速范圍為4或5比1，最高轉速同樣受到換向條件的限制。在電動機電樞中感應的電勢與端電壓間的關系為 式中此時為輸入的電樞電流。他勵發(fā)電機的端電壓隨著負載電流的增加稍有降低，這主要是由于電樞電阻上的壓降。 他勵發(fā)電機的連接圖已經(jīng)給出，所需勵磁電流是額定電樞電流的很小一部分。在磁化曲線中，因為電樞磁勢波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。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。（在實際電機中，電刷的幾何位置大約偏移圖例中所示位置90176。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。等效電路有兩個入端口形式：（a） 從一次側看為一個U形電路，其折合后的負載阻抗的端電壓為；（b） 從二次側看為一其值為，且伴有由和引起內壓降的恒壓源。由于通常只是的很小一部分，所有誤差相當小。值得注意的是，對于一臺實際的變壓器，；同樣地。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，否則一次側提供給其損耗的功率就變了。我們從一次側無法判斷是大，小，還是小，大，正是電流和匝數(shù)的乘積在產(chǎn)生作用?；ジ写磐ū仨毴噪S負載變化而變化以改變，從而產(chǎn)生更大的一次側電流。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。在向量方程中，上式也可變換成。 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 cons