The winding of the transformer is actually coil. A winding has two threads. It can also be used to make taps in the middle of the winding terminal, and the center tap is connected to the center of the winding. A winding is made up of one or more coils.
The winding of low frequency transformer is called primary winding and secondary winding. It has one primary winding and one or more secondary winding, getting different voltage ratio or impedance ratio. All the winding of the low frequency transformer is made of copper enameled wire. The resistance of the primary winding of the step-down transformer is usually very small. The coil will be burned even if the added voltage is not very high (such as 50V). But the alternating current is different. The resistance of DC is very small, so the current will be large even with moderate DC voltage. The small resistance of DC make the coil vulnerable to be burned. But the AC impedance of the primary winding is relatively large, especially at an empty load, so the current is smaller at the rated voltage of 220V. And coils will not burn out.
The low-voltage sides of the stabilizer transformer often supply close load. Because of the low voltage, the protection level is lower. Therefore, we hope that the impedance of low and high voltage will be larger. Medium voltage usually supply far-off load, so the impedance between them is expected to be smaller. And arrangement as such just meets the requirement.