---
title: "T/F: grid connected system more stable"
subject: "Transmission and Distribution System Design"
chapter: 1
key: "semester_8/transmission_and_distribution_system_design:tf-grid-connected-more-stable"
source: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/tf-grid-connected-more-stable
site: BCT Engineering
---

# T/F: grid connected system more stable

Transmission and Distribution System Design · Chapter 1: Introduction

- Asked in: 2071 Bhadra, 1+3 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/tf-grid-connected-more-stable
- Whole chapter: https://www.bctengineer.com/md/semester_8/transmission_and_distribution_system_design/chapter-1

## Question

State whether the following statement is TRUE or FALSE. Justify your answer with a brief explanation: Grid connected power system is more stable.

## Short answer

True. A large grid has high total inertia and low Thevenin impedance, keeping frequency and voltage steady during disturbances. Shared spinning reserve further aids stability, though weak ties can cause oscillations if not controlled; overall it is more stable.

## Answer

**TRUE** (in general).

- In a large grid the total inertia ($\sum H$) of all connected machines is large, so a sudden load change or loss of a generator causes only a small change in frequency.
- The grid's low Thevenin impedance (high SCMVA) keeps bus voltages steady during disturbances; it acts like an "infinite bus" for each small plant.
- Spinning reserve is shared, so other plants pick up the load of a tripped unit.
- An isolated system has small inertia and little reserve, so frequency and voltage swing much more and it can collapse after losing one unit.

Limitation: very long weak ties may create inter-area oscillations and a fault can cascade, so a grid is more stable only when it is properly planned, protected and controlled.

## Check yourself

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

1. Generally, a grid-connected power system is:
   A. Less stable than isolated
   B. More stable
   C. Equally stable
   D. Unstable always
   Answer: B. A grid has large inertia and shared reserve so it is more stable in general. (Key point: Verdict)

2. Why does loss of a generator cause only a small frequency change in a large grid?
   A. Total inertia sum H is large
   B. Inertia is zero
   C. Frequency is not affected by inertia
   D. Loads shed automatically
   Answer: A. Large combined inertia limits the rate and size of frequency change. (Key point: Inertia effect)

3. Under what condition is a grid more stable?
   A. Whenever tie lines are long and weak
   B. Only when properly planned, protected and controlled
   C. Only if isolated
   D. Never
   Answer: B. Long weak ties may cause inter-area oscillations and cascading, so planning and control are needed. (Key point: Limitation)

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