Is the main distribution box powered directly by the substation?

Generally not.

A substation, as its name suggests, is a place where voltage is changed. It is a place where the voltage and current of electrical energy are transformed, concentrated and distributed in the power system. In order to ensure the quality of electric energy and the safety of equipment, voltage adjustment, power flow (the flow and distribution of voltage, current and power in each node and branch of the power system) control as well as transmission and distribution lines and Protection of major electrical equipment. According to the purpose, it can be divided into power substation and traction substation (for electric railways and trams). The term definition stipulated in the national standard GB 50053-94 "Design Specification for Substations of 10 kV and Below" is "AC power supply of 10 kV and below supplies power to electrical equipment after being transformed by a power transformer". Those that comply with this are substations Place.