AC was chosen because higher voltages are more efficient to transmit; a transformer that works with AC power can be made with some wire and an iron nail. To convert DC power semiconductors are needed that can switch quickly; those didn't exist for about 50 years after electricity was wide spread. toomuchtodo's deleted comment also adds: > (HV)DC requires less conductor per unit distance than an AC line, as there is no need to support three phases and there is no skin effect. AC systems use a higher peak voltage for the same power, increasing insulator costs.