---
title: "Merits and demerits of interconnected system"
subject: "Power System Analysis II"
chapter: 1
key: "semester_5/power_system_analysis_ii:interconnection-merits-demerits"
source: https://www.bctengineer.com/q/semester_5/power_system_analysis_ii/interconnection-merits-demerits
site: BCT Engineering
---

# Merits and demerits of interconnected system

Power System Analysis II · Chapter 1: Interconnected Power System

- Asked in: 2071 Shrawan, 5 marks; 2070 Asar, 4 marks; 2068 Chaitra, 1+5 marks (asked 3 times)
- Video: [interconnected grid system and its advantages and disadvantages | jitendra sah](https://www.youtube.com/watch?v=kMWhCeUgYz0) — jitendra sah
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/power_system_analysis_ii/interconnection-merits-demerits
- Whole chapter: https://www.bctengineer.com/md/semester_5/power_system_analysis_ii/chapter-1

## Question

What do you mean by interconnected power system? Describe the advantages (merits) and the limitations (demerits) of interconnected power system over an isolated system.

## Short answer

Interconnected system ties multiple stations together. Merits: high reliability, lower reserve, load diversity, economy, larger units, power exchange, frequency stability, flexible maintenance. Demerits: higher fault levels, cascading failures risk, stability issues, complex control, need for coordination, higher tie-line capital cost.

## Answer

An **interconnected power system** is a system in which several generating stations and areas are linked together by transmission lines (tie-lines) and run in synchronism, so that all generators jointly supply the total load. An **isolated system** is a single station feeding its own load.

#### Merits (advantages)
1. **Reliability and continuity:** a failed unit's load is taken up by other stations.
2. **Lower reserve requirement:** reserve capacity is pooled for the whole system.
3. **Load diversity:** different areas peak at different times, so less total capacity is needed; better load factor.
4. **Economy:** cheapest generation is used first (economic dispatch); costly peaking plants run less.
5. **Large efficient units** can be installed.
6. **Power exchange:** surplus energy can be sold and deficit bought (e.g. Nepal–India cross-border trade).
7. **Better frequency stability** due to large total inertia.
8. **Flexible maintenance** scheduling.

#### Demerits (limitations)
1. **Higher fault level:** more sources feed a fault, so circuit breakers of higher rupturing capacity are needed.
2. **Cascading failures:** a disturbance in one area can spread and cause a wide-area blackout if not isolated quickly.
3. **Stability problems:** long tie-lines and many machines make transient and dynamic stability harder to maintain; inter-area oscillations can occur.
4. **Complex control and protection:** load-frequency control, voltage control, tie-line scheduling and protection coordination become complex.
5. **Need for coordination** among utilities or countries on frequency, scheduling and tariffs.
6. **High capital cost** of tie-lines, substations and communication (SCADA) systems.

| Point | Interconnected | Isolated |
|---|---|---|
| Reliability | High | Low |
| Reserve needed | Less | More |
| Fault level | High | Low |
| Control | Complex | Simple |

## Check yourself

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

1. Why do interconnected systems need higher-rated circuit breakers?
   A. Voltage is lower
   B. Reserve is shared
   C. Frequency is more stable
   D. More sources feed a fault, raising the fault level
   Answer: D. Higher fault level demands higher rupturing capacity. (Key point: Fault level)

2. A key demerit related to disturbances is:
   A. a disturbance in one area can cascade and cause a wide-area blackout
   B. faults are always confined locally
   C. less reserve is available
   D. simpler control
   Answer: A. Wide coupling lets disturbances spread. (Key point: Cascading)

3. Which pair is correct for interconnected versus isolated systems?
   A. Interconnected: more reserve needed, simple control
   B. Interconnected: less reserve needed, but more complex control
   C. Interconnected: lower reliability, low fault level
   D. Interconnected: low fault level, complex control
   Answer: B. Reserve is pooled, but control and protection become complex. (Key point: Merit vs demerit)

## Related in Power System Analysis II

- [Advantages of interconnected power system](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Ainterconnection-advantages) — Power System Analysis II, chapter 1, asked 3×
- [Real power/frequency control in interconnected system](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Areal-power-frequency-control) — Power System Analysis II, chapter 1
- [Interconnected system load-frequency and Q-V control](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Ainterconnection-control-schematic) — Power System Analysis II, chapter 1
- [Interconnection advantages and real power-frequency balance](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Ainterconnection-advantages-frequency) — Power System Analysis II, chapter 1, asked 3×
- [Line currents with isolated and grounded neutral](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Astar-impedance-unbalanced-voltages-neutral) — Power System Analysis II, chapter 4
- [Fault currents of isolated-neutral 380 V generator](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Agenerator-faults-380v-isolated-neutral) — Power System Analysis II, chapter 5

## Related in other subjects

- [Interconnected system SLD, isolated vs interconnected, advantages](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Ainterconnected-sld-isolated-advantages) — Power System Analysis I, chapter 1
- [SLD of interconnected system vs isolated system](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Ainterconnected-sld-vs-isolated) — Power System Analysis I, chapter 1
- [Merits and demerits of grid connected system](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Agrid-connected-merits-demerits) — Transmission and Distribution System Design, chapter 1
- [Interconnected power system and advantages](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Ainterconnected-system-advantages) — Power System Analysis I, chapter 1