Short note: Power supply system

A power supply system carries electrical energy from generating stations to consumers. It has four main stages.

 Generating  -> Step-up   -> Transmission -> Step-down  -> Distribution -> Consumer
 station        transformer    line           substation     (11 kV/400 V)
 (11 kV)       (132/220 kV)   (HV)           (33/11 kV)

1. Generation: power is generated at about 11 kV, 3-phase, 50 Hz by synchronous generators in hydro, thermal, solar and other plants (in Nepal, mostly hydro).
2. Transmission: transformers raise the voltage to 66, 132, 220 or 400 kV, so that the current and the $I^2R$ loss are small over long distances on overhead lines.
3. Sub-transmission/primary distribution: step-down substations reduce the voltage to 33 kV or 11 kV for towns and industries.
4. Secondary distribution: distribution transformers step the voltage down to 400 V (line) / 230 V (phase) on a three-phase four-wire system, with 230 V single phase supplied to homes.

Systems of supply: AC (usually) or DC; single-phase two-wire; three-phase three-wire (transmission); three-phase four-wire (distribution). The distribution layout may be radial, ring or interconnected, to improve reliability.

In Nepal, the Nepal Electricity Authority (NEA) operates the grid, and the standard consumer supply is 230 V single phase / 400 V three phase, 50 Hz.