The following show the idea how a Thevenin equivalent source is used to replace the primary circuit of transformer. https://www.dropbox.com/s/0kaazx1d1srgirz/reflectedsource.jpg?dl=0 https://www.dropbox.com/s/0kaazx1d1srgirz/reflectedsource.jpg?dl=0 In textbook it is commonly stated that the load impedance sees an equivalent source and the open-circuit voltage is given by Voc=NV1=NVs, usually it is said that there is no voltage drop across the source impedance therefore V1=Vs in this equation. However, the primary circuit itself is a closed circuit, there should be some current and voltage drop across impedance of the supply, how V1 can be equals to Vs? The second question is, the short circuit current is found by NIsc=Vs/Zs. It implies that when the secondary circuit is shorted, the primary current will be Vs/Zs. It seems that in this case the impedance of the primary coil is ignored. Why?