【正文】 his is further justified in that it is rarely necessary to predict transformer performance to such accuracies. Since the voltage drops are all directly proportional to the load current, it means that at noload conditions there will be no voltage drops in either winding.變壓器1. 介紹要從遠(yuǎn)端發(fā)電廠送出電能，必須應(yīng)用高壓輸電。典型的效率范圍在92到99%，上限值適用于大功率變壓器。外加電壓在一次側(cè)繞組中產(chǎn)生一個(gè)小電流Iθ。這個(gè)電流分量向鐵芯提供用于損耗的電流。的相位差。因此Ep = 并且Es = 其中Np和Es是一次側(cè)繞組和二次側(cè)繞組的匝數(shù)。 終端電壓的比率變化有些根據(jù)負(fù)載和它的功率因素。顯然，鐵芯中的電磁通形成了連接原邊和副邊的回路。如果點(diǎn)號(hào)同在線圈的上端，就意味著它們的極性相同。因此，NsIs所產(chǎn)生的磁動(dòng)勢(shì)會(huì)使主磁通φ0減小。它的磁動(dòng)勢(shì)NpIp’只停留在一次側(cè)。另外，流過(guò)一次側(cè)繞組的負(fù)載電流只在一次側(cè)繞組中產(chǎn)生磁通，這個(gè)磁通被稱(chēng)為一次側(cè)的漏磁。這證明了它對(duì)我們分析變壓器時(shí)所產(chǎn)生的影響微乎其微。另外，兩側(cè)繞組同樣具有阻抗，這也將產(chǎn)生一個(gè)電阻壓降。因?yàn)樵谶@種狀況下鐵芯的磁通是恒定的?？偟膩?lái)說(shuō)，變壓器為了保持磁通是常數(shù)，對(duì)磁通變化的響應(yīng)是瞬時(shí)的。當(dāng)變壓器帶負(fù)荷運(yùn)行時(shí)，將有電流Is流過(guò)二次側(cè)，因?yàn)镋s產(chǎn)生的感應(yīng)電動(dòng)勢(shì)相當(dāng)于一個(gè)電壓源。根據(jù)Vs和Is，可得Vp和Ip的比例是 = = 但是Vs / Is 負(fù)荷阻抗ZL，因此我們可以這樣表示Zm (primary) = a2ZL這個(gè)等式表明二次側(cè)連接的阻抗折算到電源側(cè)，其值為原來(lái)的a2倍。在一個(gè)降壓變壓器中傳輸變比a遠(yuǎn)大于1(a)，同樣的，一個(gè)升壓變壓器的變比小于1(a)。因此Pm = Pout或者VpIp primary PF = VsIs secondary PF這里PF代表功率因素。原邊的電壓和它產(chǎn)生的磁通波形是正弦形的；因此產(chǎn)生電動(dòng)勢(shì)Ep和Es的值是做正弦變化的。因?yàn)橐淮蝹?cè)繞組中的磁通會(huì)通過(guò)二次繞組，依據(jù)法拉第電磁感應(yīng)定律，二次側(cè)繞組中將產(chǎn)生一個(gè)電動(dòng)勢(shì)E，即E=NΔφ/Δt。因?yàn)樵诳蛰d時(shí)，原邊繞組中的鐵芯相當(dāng)于一個(gè)很大的電抗，空載電流的相位大約將滯后于原邊電壓相位90186。磁通是變化的；因此依據(jù)楞次定律，電磁感應(yīng)在二次側(cè)產(chǎn)生了電壓。2. 雙繞組變壓器變壓器的最簡(jiǎn)單形式包括兩個(gè)磁通相互耦合的固定線圈。 thusE = Since the same flux links with the primary and secondary windings, the voltage per turn in each winding is the same. HenceEp = andEs = where Ep and Es are the number of turn on the primary and secondary windings, respectively. The ratio of primary to secondary induced voltage is called the transformation ratio. Denoting this ratio by a, it is seen thata = = Assume that the output power of a transformer equals its input power, not a bad sumption in practice considering the high efficiencies. What we really are saying is that we are dealing with an ideal transformer。 therefore, it induces a voltage in the secondary by electromagnetic induction in accordance with Lenz’s law. Thus the primary receives its power from the source while the secondary supplies this power to the load. This action is known as transformer action.3. TRANSFORMER PRINCIPLESWhen a sinusoidal voltage Vp is applied to the primary with the secondary opencircuited, there will be no energy transfer. The impressed voltage causes a small current Iθ to flow in the primary winding. This noload current has two functions: (1) it produces the magnetic flux in the core, which varies sinusoidally between zero and φm, where φm is the maximum value of the core flux。, therefore, they are 180186。因?yàn)樽罱K的負(fù)荷，在一些點(diǎn)高電壓必須降低。從交流電源流入電流的一側(cè)被稱(chēng)為變壓器的一次側(cè)繞組或者是原邊。這個(gè)空載電流有兩項(xiàng)功能：（1）在鐵芯中產(chǎn)生電磁通，該磁通在零和φm之間做正弦變化，φm是鐵芯磁通的最大值；（2）它的一個(gè)分量說(shuō)明了鐵芯中的渦流和磁滯損耗。兩個(gè)相量的分量和代表空載電流，即I0 = Im+ Ie應(yīng)注意的是空載電流是畸變和非正弦形的。因?yàn)闆](méi)有電流流過(guò)二次側(cè)繞組，Es=Vs。一次側(cè)和二次側(cè)電壓增長(zhǎng)的比率稱(chēng)做變比。實(shí)際上, 變比從標(biāo)識(shí)牌數(shù)據(jù)獲得, 列出在滿(mǎn)載情況下原邊和副邊電壓。在第四部分我們會(huì)了解到當(dāng)變壓器帶負(fù)荷運(yùn)行時(shí)一次側(cè)繞組電流是如何隨著二次側(cè)負(fù)荷電流變化而變化的。因此當(dāng)二次側(cè)連接著一個(gè)負(fù)載時(shí)，在瞬間就有一個(gè)負(fù)荷電流沿著這個(gè)方向產(chǎn)生。這意味著一次側(cè)線圈中的磁通減少，因而它的電壓Ep將會(huì)增大。因?yàn)殍F芯的磁通φ0保持不變，變壓器空載時(shí)空載電流I0必定會(huì)為其提供能量。二次側(cè)漏磁將使電壓增大以保持兩側(cè)電壓的平衡。因?yàn)殡妷航蹬c負(fù)載電流成比例關(guān)系，這就意味著空