---
title: "Transmission expansion planning procedure"
subject: "Power Plant Design"
chapter: 2
key: "semester_8/power_plant_design:transmission-expansion-procedure"
source: https://www.bctengineer.com/q/semester_8/power_plant_design/transmission-expansion-procedure
site: BCT Engineering
---

# Transmission expansion planning procedure

Power Plant Design · Chapter 2: Integrated System Planning in Design Approach

- Asked in: 2077 Chaitra, 6 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/power_plant_design/transmission-expansion-procedure
- Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-2

## Question

What is Transmission Expansion Planning? Discuss its brief procedure.

## Short answer

Transmission expansion planning decides future lines and substations. Its procedure: use load and generation inputs, model existing network, set criteria, run load flow to find overloads, propose candidates, evaluate technically and economically, check environmental impacts, and schedule the least-cost plan.

## Answer

**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

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

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What are the first inputs of TEP?
   A. Relay settings
   B. Load forecast by substation and the generation expansion plan
   C. Fuel prices only
   D. Tower paint
   Answer: B. Future load and plant locations/years drive the network need. (Key point: Inputs)

2. What is the purpose of the base-case load flow for future years?
   A. To select tower colour
   B. To find overloaded lines, low voltages and stranded generation
   C. To set tariffs
   D. To measure rainfall
   Answer: B. It reveals where the existing network fails so that candidates can be proposed. (Key point: Base-case study)

3. Which studies are done for each alternative?
   A. Load flow, N-1 contingency, short-circuit and transient stability
   B. Only cost
   C. Only route survey
   D. Only meter reading
   Answer: A. Technical evaluation checks security, fault levels and stability. (Key point: Technical evaluation)

4. How is the best alternative chosen?
   A. Lowest voltage
   B. Shortest line
   C. Present worth of investment plus cost of losses plus unserved energy; least-cost chosen
   D. Most substations
   Answer: C. Economic evaluation compares PV of total cost and picks the least-cost option meeting the criteria. (Key point: Economic selection)

## Related in Power Plant Design

- [Transmission and distribution planning procedure](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aplanning-transmission-distribution) — Power Plant Design, chapter 2
- [Generation expansion planning procedure](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Ageneration-expansion-procedure) — Power Plant Design, chapter 2, asked 3×
- [Transmission expansion planning in deregulated market](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Atransmission-planning-deregulated) — Power Plant Design, chapter 2
- [Transmission expansion planning and applicability](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Atransmission-expansion-applicability) — Power Plant Design, chapter 2
- [Generation and distribution planning procedure](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aplanning-generation-distribution) — Power Plant Design, chapter 2
- [Power system expansion planning for a utility](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aexpansion-planning-national-utility) — Power Plant Design, chapter 2

## Related in other subjects

- [Interconnected system and transmission planning](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Ainterconnected-system-planning) — Transmission and Distribution System Design, chapter 1