Substation autotransformers transfer the incoming high voltage to the next lower voltage level. As an example, incoming high voltage of 400 kV would be transferred down to 220 kV.
In general substation autotransformers are equipped with on-load tap-changers (OLTC). Incoming transmission lines are connected to the transformers through bushings and cables through cable boxes and cable sealing ends.
Autotransformers are built in core form with auto connected windings, ie common main winding and a separate low voltage winding.