Regional interconnection and reserve bottling

Interconnection of regional utilities means linking separate utility grids by tie-lines so they operate as one larger, coordinated system.

Help in integrated system planning

1. Joint generation planning: Plants can be planned for the combined region; the cheapest sites (e.g. Nepal hydro) can serve demand anywhere in the interconnected system.
2. Reserve sharing: Each utility can hold less reserve, because outages rarely happen in both systems together; total reserve requirement falls.
3. Load diversity: Peaks of regions occur at different times or seasons, so the combined peak is lower than the sum of separate peaks.
4. Seasonal complementarity: Hydro-rich Nepal has wet-season surplus, while India's demand is high in summer; Nepal can import from India in the dry season.
5. Larger unit sizes and economies of scale, and economic dispatch over a wide area.
6. Better reliability and frequency stability due to higher combined inertia.
7. Integration of renewables over a larger area.

Does it solve "reserve bottling"?

Reserve bottling means reserve capacity that exists in one area but cannot be delivered to where it is needed because of limited transmission (tie-line) capacity; the reserve is "bottled up".

• Interconnection reduces reserve bottling because reserve in one region can now flow to the other.
• But it solves it only if tie-line transfer capacity is adequate (sized for the largest contingency, with N-1 security). If tie-lines are weak or congested, reserve remains bottled.
• So planning must include strong tie-lines (e.g. 400 kV Nepal–India double circuit lines), coordinated reserve agreements and market rules for reserve exchange.

Hence, interconnection with sufficient transfer capacity largely solves reserve bottling; a weak interconnection does not.