Transmission & Distribution (T&D) refers to the different stages of transporting electricity over poles and wires from generators to a home or a business. The main difference between the two is the voltage level at which electricity moves in each stage.
Transmission lines serve to connect power plants to substations, which can run electricity over vast distances at a high voltage, ranging from 69 kV to 765 kV. A unique feature of transmission lines is that they are bi-directional, allowing for a balanced power grid.
Distribution lines have lower voltages, ranging from 4kV to 69kV, and are used to bring electricity from substations to your home or business. The lines are smaller and cover shorter distances. Compared to transmission lines, distribution lines are passive systems, as they are not actively managed by operators or computer programs. Also, since they are traditionally uni-directional in power flow (from high voltage to low voltage), they do not require much maintenance.