It has been shown that a primary input voltage can be transformed to any desired open-circuit secondary voltage by a suitable choice of turn’s ratio. is available for circulating a load current impedance. For the moment, a lagging power factor will be considered. The secondary current and the resulting ampere-turns will change the flux, tending to demagnetize the core, reduce and with it . Because the primary leakage impedance drop is so low, a small alteration to will cause an appreciable increase of primary current from to a new value of equal to . The extra primary current and ampere-turns nearly cancel the whole of the secondary ampere-turns. This being so, the mutual flux suffers only a slight modification and requires practically the same net ampere-turns as on no load. The total primary ampere-turns are increased by an amount necessary to neutralize the same amount of secondary ampere-turns. In the vector equation, ; alternatively, . At full load, the

通過選擇合適的匝數(shù)比，一次側(cè)輸入電壓 可任意轉(zhuǎn)換成所希望的二次側(cè)開路電壓 。 可用于產(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。現(xiàn)在，我們要討論一種滯后功率因數(shù)。二次側(cè)電流及其總安匝 將影響磁通，有一種對鐵芯產(chǎn)生去磁、減小 和 的趨向。因為一次側(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 增大至一個新值 。增加的一次側(cè)電流和磁勢近似平衡了全部二次側(cè)磁勢。這樣的話，互感磁通只經(jīng)歷很小的變化，并且實際上只需要與空載時相同的凈磁勢 。一次側(cè)總磁勢增加了 ，它是平衡同量的二次側(cè)磁勢所必需的。在向量方程中， ，上式也可變換成 。滿載時，電流 只約占滿載電流的5%，因而 近似等于