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【正文】 thus E = Since the same flux links with the primary and secondary windings, the voltage per turn in each winding is the same. Hence Ep = and Es = 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 that a = psEE = psNN 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 electromagic 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 PRINCIPLES When 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 magic flux in the core, which varies sinusoidally between zero and ? φm, where φm is the maximum value of the core flux。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。 總的來說，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。從等式 psVV = psII ≌ psEE ≌ a中我們可知 Vp = aVs 并且 Ip = Is/a。如果這個(gè)電壓是升高的，它就是一個(gè)升壓變壓器。實(shí)際上我們是考慮一臺(tái)理想 狀態(tài)下的變壓器；這意味著它沒有任何損耗。因此原邊電壓很小，并且 Vp 的值近乎等于 Ep。 如果假定 變壓器中沒有其他的電能損耗一次側(cè)的感應(yīng)電動(dòng)勢(shì) Ep 和二次側(cè)的感應(yīng)電壓 Es 可以表示出來。 變壓器空載 電流 Iθ 一般大約只有滿載電流的 2%— 5%。磁通連接的第二個(gè)繞組被稱為變壓器的二次側(cè)繞組或者是副邊。本文我們討論的原則和電力變壓器 的應(yīng)用。變壓器 摘要 ： 變壓器是變電所的主要設(shè)備，功能是實(shí)現(xiàn)電網(wǎng)電壓的等級(jí)變換，基本工作原理是電磁感應(yīng)。 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。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。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。因?yàn)橐淮蝹?cè)繞組中的磁通會(huì)通過二次繞組，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。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。因此 Pm = Pout 或者 VpIp primary PF = VsIs secondary PF 這里 PF 代表功率因素。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)。根據(jù) Vs 和 Is，可得 Vp 和 Ip 的比例是 ppVI = /ssaVIa = 2ssaVI 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)，其值為原來的 a2 倍。更重要的是，在空載和滿載時(shí)，主磁通 φ0 的降落是很少的（一般在） 1 至 3%。因此我們?nèi)耘f可以認(rèn)定空載電流 I0相對(duì)于滿載電流是極其小的。把這些附加的電壓降也考慮在內(nèi)，這樣一個(gè)實(shí)際的變壓器的等值電路圖就完成了。 and (2) it provides a ponent to account for the hysteresis and eddy current losses in the core. There bined losses are normally referred to as the core losses. The noload current Iθ is usually few percent of the rated fullload current of the transformer (about 2 to 5%). Since at noload the primary winding acts as a large reactance due to the iron core, the noload current will lag the primary voltage by nearly 90186。 that is, it has no losses. Thus Pm = Pout or VpIp primary PF = VsIs secondary PF where PF is the power factor. For the abovestated assumption it means that the power factor on primary and secondary sides are equal。 thus the induced quantities E
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