【正文】 2212 )/(39。2R , 39。 ., the machine may supply its own excitation. The method of excitation profoundly influences not only the steadystate characteristics, but also the dynamic behavior of the machine in control systems. The connection 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 amount of power in the armature circuit。然而此時(shí)卻存在磁通的重新分配，由于 1? 隨 1I 的增加而增加，互感磁通分量已經(jīng)減小。在周期性交變中，有一次側(cè)漏磁通為零的瞬時(shí)，也有二次側(cè)漏磁通為零的瞬時(shí)，還有它們處于同一方向的瞬時(shí)。 RNNR ? ， 22212 )/(39。2R ， 39。 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(huì)發(fā)生。通過(guò)并勵(lì)、串勵(lì)和特勵(lì)繞組的各種不同組合，直流電機(jī)可設(shè)計(jì)成在動(dòng)態(tài)和穩(wěn)態(tài)運(yùn)行時(shí)呈現(xiàn)出寬廣范圍變化的伏 安或速度 轉(zhuǎn)矩特性。 電角度，其正弦值等于 1，則對(duì)于一臺(tái) P 極電機(jī) 12)2(2 ad FPT ??? 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(fù)號(hào)已經(jīng)去掉。 直流電機(jī)的突出優(yōu)點(diǎn)是通過(guò)選擇磁場(chǎng)繞組不同的勵(lì)磁方法，可以獲得變化范圍很大的運(yùn)行特性。不論是并勵(lì)還是復(fù)勵(lì)發(fā)電機(jī)的電壓都可借助并勵(lì)磁場(chǎng)中的變阻器在適度的范圍內(nèi)得到調(diào)節(jié)。通過(guò)改變外施電樞 電壓，可以獲得很寬的調(diào)速范圍。串勵(lì)發(fā)電機(jī)中的勵(lì)磁電流與負(fù)載電流 相同，這樣，氣隙磁通和電壓隨負(fù)載變化很大，因此很少采用串勵(lì)發(fā)電機(jī)。這種假設(shè)有必要在后述部分加以驗(yàn)證，屆時(shí)飽 和效應(yīng)會(huì)深入研究。電角度，這是因?yàn)樵哪┒诵螤顦?gòu)成圖示結(jié)果與換向器相連。在這種電路中有時(shí)可省略激磁支路，這樣電路簡(jiǎn)化為一臺(tái)產(chǎn)生恒值電壓 1E（實(shí)際上等于 1V ）并帶有阻抗 jXR? （實(shí)際上等于 11Re jXe? ）的發(fā)電機(jī)。在運(yùn)用這種理想轉(zhuǎn)換之前，內(nèi)部電壓和功率損耗已進(jìn)行了計(jì)算。39。 對(duì)于阻抗，由于二次側(cè)電壓 V 變成 VNN )/( 21 ，電流 I 變?yōu)?INN )/( 12 ，因此 阻 抗 值 ， 包 括 負(fù) 載 阻 抗 必 然 變 為 IVNNIV /)/(39。此時(shí) 1E 的幅值已經(jīng)增大，但由于 1E 與 1V 是向量合成，因此一次側(cè)電流仍然是增大的。滿載時(shí)，電流 0I 只約占滿載電流的 5%，因而 1I 近似等于122 /NNI 。 for convenience we shall continue to assume a sinusoidal fluxdensity wave in the air gap. The torque can then be found from the magic field viewpoint. The torque can be expressed in terms of the interaction of the directaxis airgap flux per pole d? and the spacefundamental ponent 1aF of the armature . 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 machine 12)2(2 adFPT ??? In which the minus sign has been dropped because the positive direction of the torque can be determined from physical reasoning. The space fundamental 1aF of the saw tooth armature . wave is 8/ 2? times its peak. Substitution in above equation then gives adaada iKimPCT ??? ?? 2 Where ai =current in external armature circuit。39。1 The Transformer on load﹠ Introduction to DC Machines The Transformer on load It has been shown that a primary input voltage 1V can be transformed to any desired opencircuit secondary voltage 2E by a suitable choice of turn’s ratio. 2E is available for circulating a load current impedance. For the moment, a lagging power factor will be considered. The secondary current and the resulting ampereturns 22NI will change the flux, tending to demagize the core, reduce m? and with it 1E . Because the primary leakage impedance drop is so low, a small alteration to 1E will cause an appreciable increase of primary current from 0I to a new value of 1I equal to ? ? ? ?ijXREV ?? 111 / . The extra primary current and ampereturns nearly cancel the whole of the secondary ampereturns. This being so, the mutual flux suffers only a slight modification and requires practically the same ampereturns 10NI as on no load. The total primary ampereturns are increased by an amount 22NI necessary to neutralize the same amount of secondary ampereturns. In the vector equation, 102211 NININI ?? 。 22 XI . The referred secondary 2212221222 )/()/(39。 aC =total number of conductors in armature winding。記住 2121 / NNEE ? ，近似等于 11IE 的輸入容量也就近似等于輸出容量 22IE 。 從上述圖中，還應(yīng)得出兩點(diǎn)：首先，為方便起見已假設(shè)匝數(shù)比為 1，這樣可使 39。/39。 IENNINNEIEk V A ???? 。當(dāng)在電路中選擇了適當(dāng)?shù)膮?shù)時(shí)，在一、二次側(cè)兩端測(cè)得的變壓器運(yùn)行情況與在該電路相應(yīng)端所測(cè)得的請(qǐng)況是完全一致的。 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(jì)算時(shí)間。） 19 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(wú)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(chǎng)分析著手求得轉(zhuǎn)矩。因?yàn)殡姌须妱?shì)與磁通成正比，所以通常用恒定轉(zhuǎn)速 0mw 下的電樞電勢(shì) 0ae 來(lái)表示磁化曲線更為方便。并勵(lì)發(fā)電機(jī)電壓隨負(fù)載增加會(huì)有所下降，但在許多應(yīng)用場(chǎng)合，這并不防礙使用。 在串勵(lì)電動(dòng)機(jī)中，電樞電流、電樞電勢(shì)和定子磁場(chǎng)磁通。通常，并勵(lì)繞組匝數(shù)多，導(dǎo)線細(xì)；而繞在外部的串勵(lì)繞組由于它必須承載電機(jī)的整個(gè)電樞電流，所以其構(gòu)成的導(dǎo)線相對(duì)較粗。 在一個(gè)相當(dāng)寬的勵(lì)磁范圍內(nèi)，鐵磁材料部分的磁阻與氣隙磁阻相比可以忽略不計(jì)，在此范圍內(nèi)磁通與勵(lì)磁繞組總磁勢(shì)呈線性比例，比例常數(shù)便是直軸氣隙磁導(dǎo)率。電刷處于交軸時(shí)，磁場(chǎng)間的角度為 90176。 直流電機(jī)導(dǎo)論 直流電機(jī)以其多功用性而形成了鮮明的特征。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。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，并用一個(gè)參數(shù)設(shè)計(jì)成 1N ， 39。因此，22212 )/(39。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。交鏈一次繞組的總磁通 111 ??????? mp 沒有變化，這是因?yàn)榭偡措妱?dòng)勢(shì) dtdNE /111 ??仍然與 1V 相等且反向。 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 .