An electricity transmission system is a highly interconnected network designed to move power efficiently from where it's generated to where it's consumed. The five primary components are:

1. Power Plants (Generation): This is the starting point where electricity is produced from various sources like fossil fuels, nuclear energy, or renewables.

2. Transformers: These are critical devices that change the voltage of electricity. They are used to step up the voltage at the generating station for efficient, long-distance transmission and to step down the voltage at substations.

3. Transmission Towers & Poles: These robust structures, made of steel or concrete, are the backbone of the overhead transmission system. They physically support the conductors and insulators, keeping them safely above the ground.

4. Conductors & Cables: These are the wires that carry the electricity. They are typically made of materials like aluminum with a steel core for strength and are strung between the towers. For underground projects, insulated cables are used.

5. Substations: Acting as the "traffic managers" of the grid, substations house transformers, switchgear, and control equipment to adjust voltage levels, switch circuits on or off, and protect the system from faults.