---
title: "Need for interconnection into a grid"
subject: "Power System Analysis I"
chapter: 1
key: "semester_4/power_system_analysis_i:need-interconnection-grid"
source: https://www.bctengineer.com/q/semester_4/power_system_analysis_i/need-interconnection-grid
site: BCT Engineering
---

# Need for interconnection into a grid

Power System Analysis I · Chapter 1: General Background

- Asked in: 2069 Poush, 6 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/power_system_analysis_i/need-interconnection-grid
- Whole chapter: https://www.bctengineer.com/md/semester_4/power_system_analysis_i/chapter-1

## Question

Justify the need of interconnection of different generating stations by high voltage lines to form a power grid.

## Short answer

Interconnection enhances reliability by sharing reserves, allows economic dispatch of cheapest plants first, reduces combined peak through load diversity, and enables remote hydro to supply cities. High voltage lines minimize I²R losses and voltage drop for long-distance bulk power transfer.

## Answer

A **power grid** is formed by interconnecting generating stations and load centres by high-voltage transmission lines so that all plants operate in parallel and supply the combined load. This interconnection is needed for the following reasons.

1. **Reliability and continuity:** If one generator or plant trips, the others in the grid supply its load; consumers do not lose supply.
2. **Reduced reserve capacity:** Each isolated station needs its own standby units. In a grid, the spinning reserve is shared, so total installed capacity required is lower.
3. **Economic operation:** The most efficient and cheapest plants (e.g. run-of-river hydro) are run at full load and costly plants only at peak, i.e. economic load dispatch.
4. **Load diversity:** Peak demands of different regions occur at different times. Interconnection lowers the combined peak, so less capacity is needed (higher diversity factor).
5. **Using remote resources:** Hydro sites in mountains can supply cities far away; seasonal surplus in one area can supply another.
6. **Seasonal and cross-border exchange:** Nepal exports surplus hydro power in the wet season and imports in the dry season through 132/220/400 kV links with India.
7. **Larger, efficient units:** Grid can absorb large generating units, which have lower cost per kW.
8. **Stable voltage and frequency:** A large system is "stiff"; load changes cause negligible voltage and frequency variation.
9. **Better use of transmission:** Power can flow over parallel paths, reducing overload.

#### Why high voltage lines
Interconnecting lines carry large power over long distances. Since loss $\propto P^2R/V^2$ and capacity $\propto V^2$, only high voltages (132–400 kV) make such transfer efficient and stable.

```text
 Plant A ====132 kV==== Plant B
    \                   /
     \== Load centre ==/
          ||
      Tie to neighbour grid
```

Drawbacks such as higher fault levels and spread of disturbances are handled by good protection and control, so interconnection is fully justified.

## Check yourself

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

1. How does a grid reduce reserve capacity?
   A. Every station has its own reserve
   B. No reserve is needed
   C. Spinning reserve is shared
   D. Reserve increases
   Answer: C. Shared reserve lowers total installed capacity. (Key point: Reserve)

2. Why does interconnection lower the combined peak?
   A. Regional peaks occur at different times
   B. All peaks coincide
   C. Loads are removed
   D. Voltage increases
   Answer: A. Diversity of peaks lowers the combined maximum demand. (Key point: Load diversity)

3. In a grid, cheapest plants are run
   A. At peak only
   B. Never
   C. Equally
   D. At full load, costly plants only at peak
   Answer: D. This is economic load dispatch. (Key point: Economic operation)

4. Interconnecting lines are high voltage because
   A. Loss increases with V
   B. Capacity falls with V
   C. Loss is proportional to P^2R/V^2 and capacity to V^2
   D. Insulation is free
   Answer: C. High V makes bulk transfer efficient and stable. (Key point: Why high voltage)

## Related in Power System Analysis I

- [Need for different voltage levels](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Aneed-different-voltage-levels) — Power System Analysis I, chapter 1, asked 3×
- [Conductor volume vs voltage and power factor](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Aconductor-volume-voltage-pf) — Power System Analysis I, chapter 1
- [Typical power system with voltage levels](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Atypical-power-system-voltage-levels) — Power System Analysis I, chapter 1
- [Reactive power proportional to voltage drop](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Areactive-power-voltage-drop) — Power System Analysis I, chapter 6
- [Need and methods of reactive power compensation](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Areactive-compensation-need-methods) — Power System Analysis I, chapter 6, asked 2×
- [Voltage across string discs is not uniform](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Astring-voltage-not-uniform) — Power System Analysis I, chapter 2, asked 3×

## Related in other subjects

- [Justify higher voltage/more circuits for more power](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Ajustify-higher-voltage-more-circuits) — Transmission and Distribution System Design, chapter 2
- [Voltage and circuits for 250 MW grid connection](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Avoltage-circuits-250mw-grid-options) — Transmission and Distribution System Design, chapter 2
- [Voltage, circuits and discs for 260 MW grid link](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Avoltage-circuits-260mw-grid-options) — Transmission and Distribution System Design, chapter 2
- [Voltage and circuits for 180 MW grid link](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Avoltage-circuits-180mw-grid-options) — Transmission and Distribution System Design, chapter 2