Transmission expansion planning procedure

Transmission expansion planning (TEP) decides the location, voltage, capacity and timing of new transmission lines and substations needed to carry power from generating stations to load centres reliably and at minimum total cost during the planning period.

Brief procedure

 Load forecast + generation expansion plan
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 Existing network model & planning criteria
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 Base-case load flow -> find overloads / low V
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 Propose candidate lines & substations
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 Technical studies (load flow, N-1,
 short circuit, stability)
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 Economic comparison (capex + losses)
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 Select least-cost plan -> schedule

1. Collect inputs: Load forecast by substation; generation expansion plan (location and year of new plants); import/export plans.
2. Model existing network: Lines, transformers, impedances, thermal ratings.
3. Set planning criteria: N-1 security, voltage limits (e.g. 0.95–1.05 pu), line loading below thermal limit, fault level within switchgear rating, stability margin.
4. Base-case study: Run load flow for future years (wet/dry season, peak/off-peak) to find overloaded lines, low voltages and stranded generation.
5. Identify candidates: New lines, line upgrades (double circuit, higher voltage, HTLS conductor), new substations, reactive compensation.
6. Technical evaluation: Load flow, contingency (N-1), short-circuit and transient stability studies for each alternative.
7. Economic evaluation: Present worth of investment + cost of losses + cost of unserved energy; choose the least-cost alternative. Optimisation methods (linear/mixed-integer programming) can be used.
8. Environmental and social check: Route selection, right-of-way, forest areas.
9. Final plan: Prepare an implementation schedule, cost estimate and funding plan; review it periodically.