Transmission expansion planning and applicability

Transmission expansion planning (TEP) is the process of deciding which new transmission lines, substations and transformers should be built, with their voltage, capacity, route and commissioning year, so that power from present and future generators reaches the load centres reliably and at minimum cost over the planning horizon (10–20 years).

Main questions answered

• Where to build new lines/substations?
• What voltage level and conductor/capacity?
• When to commission them?

Applicability

1. Evacuation of new generation: New hydro plants in remote valleys need lines to the grid; without TEP, energy is spilled (a common problem in Nepal).
2. Meeting load growth: Supplies growing cities and industrial corridors without overloading existing lines.
3. Reliability and security: Ensures N-1 security, voltage limits and acceptable fault levels.
4. Loss reduction: Higher voltage (220/400 kV) reduces $I^2R$ losses.
5. Cross-border trade: Plans interconnections such as Dhalkebar–Muzaffarpur and Butwal–Gorakhpur 400 kV for export/import.
6. Market operation: Removes congestion, allows open access for IPPs in a deregulated market.
7. Coordination: Links generation expansion plan with distribution plan; avoids stranded generation or idle lines.

Example: NEA's Transmission System Master Plan identifies river-basin-wise 400 kV corridors (Koshi, Gandaki, Karnali) to evacuate planned hydro projects.