---
title: "Role of interconnection and reactive power control"
subject: "Power System Analysis II"
chapter: 1
key: "semester_5/power_system_analysis_ii:interconnection-reactive-control"
source: https://www.bctengineer.com/q/semester_5/power_system_analysis_ii/interconnection-reactive-control
site: BCT Engineering
---

# Role of interconnection and reactive power control

Power System Analysis II · Chapter 1: Interconnected Power System

- Asked in: 2070 Chaitra, 5 marks
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/power_system_analysis_ii/interconnection-reactive-control
- Whole chapter: https://www.bctengineer.com/md/semester_5/power_system_analysis_ii/chapter-1

## Question

Discuss role of interconnection in power system. Explain how reactive power can be controlled in power system network.

## Short answer

Interconnection increases reliability, enables reserve sharing, load diversity, and economic exchange. Reactive power is controlled by generator AVR (excitation), switched shunt capacitors/reactors, synchronous condensors, SVC/STATCOM, on-load tap changers, and series capacitors to keep voltage within limits.

## Answer

#### Role of interconnection
Interconnection ties generating stations and areas together by tie-lines so they run in synchronism and share load. Its roles are:
- **Reliability:** loss of a unit is covered by other plants.
- **Reserve sharing:** less spinning reserve per area.
- **Economy:** cheapest generation is used first; surplus power can be exchanged between areas or countries.
- **Load diversity:** lower total installed capacity.
- **Frequency stability:** large combined inertia limits frequency swings.

#### Control of reactive power
Bus voltage depends mainly on reactive power ($\Delta V \approx QX/V$), so Q is controlled to keep voltage within limits (about ±5%). Methods:

1. **Generator excitation (AVR):** raising field current increases $E_f$, so the generator supplies Q (over-excited); lowering it absorbs Q (under-excited), within the capability-curve limits.
2. **Shunt capacitors:** supply Q at heavy load, raising voltage; switched in steps.
3. **Shunt reactors:** absorb Q at light load (e.g. on long EHV lines) to limit the Ferranti rise.
4. **Synchronous condensers:** unloaded synchronous motors that give or absorb Q smoothly by excitation control.
5. **Static VAR compensators (SVC) and STATCOM:** thyristor or converter-based devices with fast, continuous Q control.
6. **Tap-changing transformers (OLTC):** redistribute Q flow and adjust secondary voltage.
7. **Series capacitors:** cancel part of line reactance, reducing the reactive drop $IX$.

## Check yourself

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

1. Shunt reactors are used to:
   A. absorb Q at light load and limit the Ferranti rise
   B. supply Q at heavy load
   C. raise frequency
   D. reduce fault level only
   Answer: A. They counteract line charging at light load. (Key point: Shunt reactors)

2. An under-excited generator:
   A. supplies reactive power
   B. absorbs reactive power
   C. supplies only P
   D. has zero armature current
   Answer: B. Lowering excitation makes the machine absorb Q. (Key point: Under-excited generator)

3. Series capacitors help voltage by:
   A. adding line resistance
   B. raising frequency
   C. cancelling part of line reactance, reducing the reactive drop IX
   D. absorbing Q
   Answer: C. Reduced net reactance lowers the drop. (Key point: Series capacitors)

## Related in Power System Analysis II

- [Reactive power injection and generation limits](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Areactive-power-injection-limits) — Power System Analysis II, chapter 1
- [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
- [Effects of real and reactive power mismatch](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Apf-qv-mismatch-effects) — Power System Analysis II, chapter 1, asked 4×
- [Reactive power and voltage balance](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Areactive-power-voltage-balance) — Power System Analysis II, chapter 1
- [Generator reactive power at constant terminal voltage](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Agenerator-reactive-power-infinite-bus) — 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

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- [Reactive power compensation and its benefits](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Areactive-compensation-meaning-benefits) — Power System Analysis I, chapter 6, asked 2×