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【正文】 出功率的增加而增加（ 2）初級線圈中的磁動勢將增加，以此來抵消二次 側(cè)中的磁動勢減小磁通的趨勢。 總的來說，變壓器為了保持磁通是常數(shù)，對磁通變化的響應(yīng)是瞬時的。更重要的是，在空載和滿載時，主磁通 φ0的降落是很少的（一般在） 1 至 3%。其需要的條件是 E 降落很多來使電流 Ip 增加。 在一次側(cè)，電流 Ip’在一次側(cè)流過以平衡 Is 產(chǎn)生的影響。它的磁動勢 NpIp’只停留在一次側(cè)。因為鐵芯的磁通 φ0保持不變，變壓器空載時空載電流 I0必定會為其提供能量。故一次側(cè)電流 Ip 是電流 Ip’與 I0’的和。 因為空載電流相對較小，那么一次側(cè)的安匝數(shù)與二次側(cè)的安匝數(shù)相等的假設(shè)是成立的。因為在這種狀況下鐵芯的 磁通是恒定的。因此我們?nèi)耘f可以認(rèn)定空載電流 I0相對于滿載電流是極其小的。 當(dāng)一個電流流過二次側(cè)繞組，它的磁動勢（ NsIs）將產(chǎn)生一個磁通，于空載電流 I0產(chǎn)生的磁通 φ0不同，它只停留在二次側(cè)繞組中。因為這個磁通不流過一次側(cè)繞組，所以它不是一個公共磁通。 另外，流過一次側(cè)繞組的負(fù)載電流只在一次側(cè)繞組中產(chǎn)生磁通，這個磁通被稱為一次側(cè)的漏磁。二次側(cè)漏磁將使電壓增大以保持兩側(cè)電壓的平衡。一次側(cè)漏磁也一樣。因此，這兩個增大的電壓具有電壓降的性質(zhì)，總稱為漏電抗電壓降。另外，兩側(cè)繞組同樣具有阻抗，這也將產(chǎn)生一個電阻壓降。把 這些附加的電壓降也考慮在內(nèi)，這樣一個實際的變壓器的等值電路圖就完成了。由于分支勵磁體現(xiàn)在電流里，為了分析我們可以將它忽略。這就符我們前面計算中可以忽略空載電流的假設(shè)。這證明了它對我們分析變壓器時所產(chǎn)生的影響微乎其微。因為電壓降與負(fù)載電流成比例關(guān)系，這就意味著空載情況下一次側(cè)和二次側(cè)繞組的電壓降都為零。 譯自 科技英語 5 原文 TRANSFORMER 1. INTRODUCTION The highvoltage transmission was need for the case electrical power is to be provided at considerable distance from a generating station. At some point this high voltage must be reduced, because ultimately is must supply a load. The transformer makes it possible for various parts of a power system to operate at different voltage levels. In this paper we discuss power transformer principles and applications. 2. TOWWINDING TRANSFORMERS A transformer in its simplest form consists of two stationary coils coupled by a mutual magic flux. The coils are said to be mutually coupled because they link a mon flux. In power applications, laminated steel core transformers (to which this paper is restricted) are used. Transformers are efficient because the rotational losses normally associated with rotating machine are absent, so relatively little power is lost when transforming power from one voltage level to another. Typical efficiencies are in the range 92 to 99%, the higher values applying to the larger power transformers. The current flowing in the coil connected to the ac source is called the primary winding or simply the primary. It sets up the flux φ in the core, which varies periodically both in magnitude and direction. The flux links the second coil, called the secondary winding or simply secondary. The flux is changing。 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。 and (2) it provides a ponent to account for the hysteresis and eddy current losses in the core. There bined losses are 鄭州大學(xué)電氣工程學(xué)院畢業(yè)論文 6 normally referred to as the core losses. The noload current Iθ is usually few percent of the rated fullload current of the transformer
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