Interconnected system SLD and functions of each part

Single line diagram

 [G] 11 kV       Step-up       Transmission
  |---->[11/220 kV]====== 220/400 kV ======+
                                            |
 [G] 11 kV                          [220/132 kV]
  |---->[11/132 kV]====== 132 kV ====== Grid S/S
                                            |
                              Sub-transmission 66/33 kV
                                            |
                                    [33/11 kV] S/S
                                            |
                              Primary distribution 11 kV
                                            |
                                    [11/0.4 kV] DT
                                            |
                         Secondary 400/230 V consumers

Function of each system

1. Generation system

• Converts primary energy (water, fuel, sun) into electrical energy in power stations at 6.6–11 kV.
• Includes turbines, alternators, exciters, governors and step-up transformers.
• Controls frequency (through governors) and voltage (through AVR).

2. Transmission system

• Carries bulk power from generating stations to major load centres at extra-high voltage (400, 220, 132 kV in Nepal).
• Interconnects power stations and neighbouring grids, allowing power exchange, sharing of reserve and economic dispatch.
• Includes towers, conductors, insulators, grid substations and protection.
• High voltage reduces current, losses and conductor cost.

Sub-transmission (66/33 kV) links grid substations to distribution substations in cities and districts.

3. Distribution system

• Delivers power from distribution substations (33/11 kV) to individual consumers.
• Primary distribution at 11 kV feeds distribution transformers and bulk consumers.
• Secondary distribution at 400 V (3-phase) / 230 V (1-phase) supplies houses, shops and small industries.
• Includes feeders, distributors, service mains, distribution transformers and meters.