--- title: "Reactive power compensation and its benefits" subject: "Power System Analysis I" chapter: 6 key: "semester_4/power_system_analysis_i:reactive-compensation-meaning-benefits" source: https://www.bctengineer.com/q/semester_4/power_system_analysis_i/reactive-compensation-meaning-benefits site: BCT Engineering --- # Reactive power compensation and its benefits Power System Analysis I · Chapter 6: Performance Analysis - Asked in: 2073 Magh, 5 marks; 2068 Magh, 4 marks (asked 2 times) - Video: [Understanding power factor and basics of reactive power compensation](https://www.youtube.com/watch?v=aRtiAp4pQT4) — The Electrical Concepts - 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/reactive-compensation-meaning-benefits - Whole chapter: https://www.bctengineer.com/md/semester_4/power_system_analysis_i/chapter-6 ## Question What is meant by reactive power compensation in an electric power system? List out its benefits to the system. ## Short answer Reactive power compensation involves adding devices that supply or absorb reactive power locally to maintain bus voltages and minimize reactive flow. Benefits: improved voltage profile, reduced losses, higher power factor, increased transfer capacity, enhanced stability, voltage stability, released generator capacity, and economic savings. ## Answer **Reactive power compensation** is the control of reactive power flow in a power system by adding devices that **supply** reactive power (capacitors, over-excited synchronous condensers, STATCOM in capacitive mode) or **absorb** it (reactors, under-excited condensers, SVC in inductive mode). The aim is to keep bus voltages within limits and to reduce reactive power flow through lines. Reactive power does no useful work but is needed for magnetic and electric fields of motors, transformers and lines. If it is carried over long distances it causes voltage drop and losses. Compensation supplies it close to where it is needed. Main types: - **Shunt compensation:** capacitors or reactors connected in parallel at buses. - **Series compensation:** capacitors connected in series with the line to cancel part of its reactance. - **Dynamic compensation:** synchronous condensers, SVC, STATCOM. #### Benefits to the system 1. **Better voltage profile:** voltage drop $\Delta V \approx (PR + QX)/V$ is reduced; overvoltage at light load (Ferranti effect) is controlled. 2. **Lower losses:** line current falls, so $I^2R$ losses in lines and transformers fall. 3. **Improved power factor**, avoiding low-p.f. penalties for consumers. 4. **More transmission capacity:** the same line and transformers can carry more active power (MW) because less of their rating is used by Mvar. 5. **Higher stability limit:** series capacitors reduce $X$ in $P = \frac{V_SV_R}{X}\sin\delta$, and shunt devices hold voltage up, improving steady-state and transient stability. 6. **Voltage stability:** prevents voltage collapse under heavy loading or contingencies. 7. **Released generation capacity:** generators supply less Mvar and can deliver more MW. 8. **Economic saving:** lower losses, deferred investment in new lines and equipment. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is reactive power compensation? A. Controlling reactive power flow by adding devices that supply or absorb Q to keep voltages within limits B. Reducing active power generation C. Converting reactive power into active power D. Increasing line resistance to damp oscillations Answer: A. Compensation supplies or absorbs Q close to where it is needed. (Key point: Meaning) 2. How does compensation reduce losses? A. It lowers the line resistance B. Less reactive current flows in lines, so line current and I^2R losses fall C. It raises the sending-end voltage D. It reduces frequency Answer: B. Supplying Q locally reduces the line current. (Key point: Loss reduction) 3. How do series capacitors improve stability limit? A. They increase X so delta is smaller B. They raise R C. They reduce X in P = VsVr sin(delta)/X, raising the maximum transfer D. They change frequency Answer: C. Lower X means higher maximum power for a given angle. (Key point: Stability) 4. How does compensation increase MW capacity of lines and transformers? A. Their MVA rating is increased physically B. Active power is generated by capacitors C. Resistance becomes zero D. Less of their rating is used by Mvar, so more MW can be carried Answer: D. Apparent power is shared between P and Q; removing Q frees capacity for P. (Key point: Capacity release) ## Related in Power System Analysis I - [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× - [Compensation does not reduce load reactive demand](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Acompensation-does-not-reduce-load-q) — Power System Analysis I, chapter 6 - [Reactive power flow between machines via j10 Ω](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Atwo-machines-reactive-j10) — Power System Analysis I, chapter 3 - [Line as source and sink of reactive power, effects](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Aline-source-sink-reactive-effects) — Power System Analysis I, chapter 6 - [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 - [Vs from P+jQ and reactive power flow direction](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Avs-from-pq-reactive-flow) — Power System Analysis I, chapter 6 ## Related in other subjects - [Power angle and series compensation](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Apower-angle-series-compensation) — Power System Analysis II, chapter 6 - [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× - [T/F: HVDC converter reactive power need](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-hvdc-reactive-power) — Transmission and Distribution System Design, chapter 1 - [Role of interconnection and reactive power control](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Ainterconnection-reactive-control) — Power System Analysis II, chapter 1