【正文】 s of saturation, so for an understanding of internal behavior.There are two ways of looking at the equivalent circuit:(a) viewed from the primary as a sink but the referred load impedance connected across ,or(b) Viewed from the secondary as a source of constant voltage with internal drops due to and. The magnetizing branch is sometimes omitted in this representation and so the circuit reduces to a generator producing a constant voltage (actually equal to ) and having an internal impedance (actually equal to ).In either case, the parameters could be referred to the secondary winding and this may save calculation time.The resistances and reactances can be obtained from two simple light load tests.Introduction to DC MachinesDC machines are characterized by their versatility. By means of various bination of shunt, series, and separately excited field windings they can be designed to display a wide variety of voltampere or speedtorque characteristics for both dynamic and steady state operation. Because of the ease with which they can be controlled, systems of DC machines are often used in applications requiring a wide range of motor speeds or precise control of motor output.The essential features of a DC machine are shown schematically. The stator has salient poles and is excited by one or more field coils. The airgap flux distribution created by the field winding is symmetrical about the centerline of the field poles. This axis is called the field axis or direct axis.As we know, the AC voltage generated in each rotating armature coil is converted to DC in the external armature terminals by means of a rotating mutator and stationary brushes to which the armature leads are connected. The mutatorbrush bination forms a mechanical rectifier, resulting in a DC armature voltage as well as an armature . wave which is fixed in space. The brushes are located so that mutation occurs when the coil sides are in the neutral zone, midway between the field poles. The axis of the armature . wave then in 90 electrical degrees from the axis of the field poles, ., 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 . 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 mutator.)The magnetic torque and the speed voltage appearing at the brushes are independent of the spatial waveform of the flux distribution。在向量方程中，上式也可變換成?；ジ写磐ū仨毴噪S負(fù)載變化而變化以改變，從而產(chǎn)生更大的一次側(cè)電流。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(cè)提供給其損耗的功率就變了。由于通常只是的很小一部分，所有誤差相當(dāng)小。勵(lì)磁繞組產(chǎn)生的氣隙通以磁極中心線為軸線對(duì)稱分布，這條軸線稱為磁場(chǎng)軸線或直軸。簡單的單個(gè)線圈的電樞中的整流電壓前面已經(jīng)討論過了。 他勵(lì)發(fā)電機(jī)的連接圖已經(jīng)給出，所需勵(lì)磁電流是額定電樞電流的很小一部分。在電動(dòng)機(jī)電樞中感應(yīng)的電勢(shì)與端電壓間的關(guān)系為 式中此時(shí)為輸入的電樞電流。差復(fù)勵(lì)連接很少使用。因此串勵(lì)電動(dòng)機(jī)是一種具有明顯下降的轉(zhuǎn)速負(fù)載特性的變速電動(dòng)機(jī)。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。將線圈和線圈并排放置在一個(gè)鐵芯的兩邊，這一點(diǎn)與實(shí)際情況之間的差別僅僅是為了方便。對(duì)于阻抗，由于二次側(cè)電壓變成，電流變?yōu)?，因此阻抗值，包括?fù)載阻抗必然變?yōu)?。這兩種漏磁通，緊密相關(guān)；例如，對(duì)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。因?yàn)橐淮蝹?cè)漏阻抗壓降如此之小，所以的微小變化都將導(dǎo)致一次側(cè)電流增加很大，從增大至一個(gè)新值。 alternatively, . At full load, the current is only about 5% of the fullload current and so is nearly equal to. Because in mind that , the input kVA which is approximately is also approximately equal to the output kVA, .The physical current has increased, and with in the primary leakage flux to which it is proportional. The total flux linking the primary, is shown unchanged because the total back ., （）is still equal and opposite to . However, there has been a redistribution of flux and the mutual ponent has fallen due to the increase of with . Although the change is small, the secondary demand could not be met without a mutual flux and . alteration to permit primary current to change. The net flux linking the secondary winding has been further reduced by the establishment of secondary leakage flux due to , and this opposes . Although and are indicated separately, they bine to one resultant in the core which will be downwards at the instant shown. Thus the secondary terminal voltage is reduced to which can be considered in two ponents, . or vectorially . As for the primary, is responsible for a substantially constant secondary leakage inductance . It will be noticed that the primary leakage flux is responsible for part of the change in the secondary terminal voltage due to its effects on the mutual flux. The two leakage fluxes are closely related?？捎糜诋a(chǎn)生負(fù)載電流，該電流的幅值和功率因數(shù)將由而次側(cè)電路的阻抗決定。這樣，二次側(cè)端電壓降至，它可被看成兩個(gè)分量，即，或者向量形式。因此，二次側(cè)繞組可用任意個(gè)在一次側(cè)產(chǎn)生相同匝數(shù)的等效繞組是方便的。的通常情形時(shí)的等效電路，它除了為了考慮鐵耗而引入了，且為了將折算回而在二次側(cè)兩端引入了一理想的無損耗轉(zhuǎn)換外，其他方面是一樣的。在這種電路中有時(shí)可省略激磁支路，這樣電路簡化為一臺(tái)產(chǎn)生恒值電壓（實(shí)際上等于）并帶有阻抗（實(shí)際上等于）的發(fā)電機(jī)。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。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。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)。通過改變外施電樞電壓，可以獲得很寬的調(diào)速范圍。直流電機(jī)的應(yīng)用優(yōu)勢(shì)在于可接成并勵(lì)、串勵(lì)和復(fù)勵(lì)等各種勵(lì)磁方式，因而可提供多種性能各異的運(yùn)行特性。由于反電勢(shì)決定于磁通和轉(zhuǎn)速，因此，轉(zhuǎn)速必須稍稍降低。自勵(lì)發(fā)電機(jī)的勵(lì)磁繞組可以有三種不同的供電方式。當(dāng)每極有十幾個(gè)換向器片，波線的波動(dòng)變得非常小，從電刷端觀察到的平均電壓等于線圈整流電壓平均值之和。電刷的放置應(yīng)使換向線圈也處于磁極中性區(qū)，即兩磁極之間。這對(duì)于高電壓和頻率超過100Hz的情形是很重要的。折算后的二次側(cè)。其次，如果橫軸像通常取的話，那么向量圖是以為零時(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。一次側(cè)電流已增大，隨之與之成正比的一次側(cè)漏磁通也增大。 =number of parallel paths through winding。 =total number of conductors in armature winding。記住，近似等于的輸入容量也就近似