【正文】 ves 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。本文我們討論的原則和電力變壓器的應(yīng)用。 變壓器空載電流 sI 一般大約只有滿載電流的 2%— 5%。因此原邊電壓很小，并且 Vp 的值近乎等于Ep。如果這個(gè)電壓是升高的，它就是一個(gè)升壓變壓器。我們把這種折算方式稱(chēng)為負(fù)載阻抗向一次側(cè)的折算。在上面公式中一次側(cè)和二次側(cè)的功率因素是相等的；因此 VpIp = VsIs 從上式我們可以得知 psVV = psII ≌ psEE ≌ a 它表明端電壓比等于匝數(shù)比，換句話說(shuō)，一次側(cè)和二次側(cè)電流比與匝數(shù)比成反比。相同的磁通會(huì)通過(guò)原邊自身，產(chǎn)生一個(gè)電動(dòng)勢(shì) Ep。變壓器在原邊接收電能的同時(shí)也在向副邊所帶的負(fù)荷輸送電能。 thus the induced quantities Ep and Es vary as a sine function. The average value of the induced voltage given by Eavg = turns c h a n g e in flu x in a g iv e n tim eg iv e n tim e which is Faraday’s law applied to a finite time interval. It follows that Eavg = N 21/(2 )mf? = 4fNφm which N is the number of turns on the winding. Form ac circuit theory, the effective or rootmeansquare (rms) voltage for a sine wave is times the average voltage。 out of phase with the applied voltage. Since no current flows in the secondary winding, Es=Vs. The noload primary current I0 is small, a few percent of fullload current. Thus the voltage in the primary is small and Vp is nearly equal to Ep. The primary voltage and the resulting flux are sinusoidal。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)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。因此 Pm = Pout 或者 VpIp primary PF = VsIs secondary PF 這里 PF 代表功率因素。根據(jù) Vs 和 Is，可得 Vp 和 Ip 的比例是 ppVI = /ssaVIa = 2 ssaVI 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)。原邊的電壓和它產(chǎn)生的