I have been learning about electricity send through long distance from the power companies to people's homes. I know that power is initially send from a power company to a transformer in high voltage, so to reduce current, which then reaches another transformer nearby people's home where current is then increased by using step down transformers. However, what I don't get here, is why do each transformers have two coils? Why can't you just work with one coils or wire where direct current with high voltage is send from power company to nearby substation, where there voltage is then decreased to increase the current that flow into people's homes? The idea of having two coils in transformers just seems redundant to me.
Edit: After, somebody pointed out that the questions is not clear, my question in short is why does transformers need two coils? Why can't it do the same job, or varying voltage and current, with only one coil, where each coils with different number of coils and in different stations, induce each other?