Step down transmission substations are located at switching points in an electrical grid. They connnect different parts of fa grid and are a source for subtransmission lines. The stepdown substation can change the transmission voltage to a subtransmission voltage, usually 69 kV. The subtransmission voltage lines can then serve as a source to distribution substations. Sometimes, power is tapped from the subtransmission line for use in an industrial facility along the way. Oterwise, the power goes to a distribution substation.