--- title: "Why reactors are used and their types" subject: "Power Plant Equipment" chapter: 4 key: "semester_7/power_plant_equipment:reactor-types" source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/reactor-types site: BCT Engineering --- # Why reactors are used and their types Power Plant Equipment · Chapter 4: Substation Equipments - Asked in: 2073 Shrawan, 5 marks - Video: [Reactor vs. Transformer | Different Types of Reactors](https://www.youtube.com/watch?v=r4KDI2ROtew) — NO MORE ratta maar - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/power_plant_equipment/reactor-types - Whole chapter: https://www.bctengineer.com/md/semester_7/power_plant_equipment/chapter-4 ## Question Why is reactor used in power system? Explain different types of reactor. ## Short answer Reactors are inductive coils used to limit short-circuit current and fault MVA, localize faults, and support voltage on healthy sections. Types include air-core, oil-immersed air-core, and oil-immersed iron-core reactors. By location they are generator, feeder, bus-bar (ring or tie-bar), and shunt reactors. ## Answer **Reactors** are coils with large inductive reactance and very small resistance. They are used in power systems mainly to **limit short-circuit current** so that circuit breakers and equipment are not over-stressed, and to localise faults. #### Why reactors are used - Fault current $I_f = V/X$; adding reactance cuts $I_f$ and the fault MVA, so cheaper breakers can be used. - Keep the voltage on healthy sections from collapsing during a fault. - Reduce mechanical forces and heating in windings during short circuits. - Shunt reactors absorb surplus VAr on long, lightly loaded lines. #### Types by construction | Type | Feature | |---|---| | Air-core (dry) | Cement/concrete former, no iron; constant reactance, no saturation; used up to about 33 kV | | Oil-immersed, air-core | Coil in oil tank; better insulation and cooling; for high voltage | | Oil-immersed, iron-core (gapped) | Smaller size; reactance may fall at high current due to saturation | #### Types by location (reactor schemes) 1. **Generator reactor:** in series with each generator. Protects the generator, but is in circuit all the time, so causes constant voltage drop and loss. Modern generators have enough internal reactance, so it is seldom used. 2. **Feeder reactor:** in series with each outgoing feeder. A fault on one feeder does not disturb the bus voltage much. But it gives no protection for bus faults, and causes drop and loss on each feeder. 3. **Bus-bar reactor:** connects sections of the bus. - **Ring system:** sections joined in a ring through reactors. - **Tie-bar system:** each section connects through a reactor to a common tie-bar; fault current from other sections passes through two reactors. #### Shunt reactor Connected between line and earth at the end of long EHV lines to absorb charging current and limit the rise of receiving-end voltage (Ferranti effect). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the main reason reactors are used in power systems? A. To improve power factor of the load B. To limit short-circuit current C. To increase the system voltage D. To raise the fault MVA Answer: B. Adding reactance reduces I_f = V/X and fault MVA, so breakers and equipment are not over-stressed. (Key point: Main purpose of reactors) 2. Which statement about air-core (dry) reactors is correct? A. Reactance falls sharply at high current due to saturation B. They are only used above 400 kV C. They have constant reactance because there is no iron to saturate D. They are always immersed in oil Answer: C. Without an iron core there is no saturation, so reactance stays constant even at fault current. (Key point: Air-core reactor features) 3. What is a drawback of the feeder reactor scheme? A. It cannot limit a feeder fault B. It gives no protection for bus-bar faults and causes drop and loss on every feeder C. It disturbs the bus voltage on feeder faults D. It must be placed in the tie-bar Answer: B. Feeder reactors are in series with the load all the time (drop and loss) and do not limit faults on the bus itself. (Key point: Feeder reactor limitation) 4. Why is a shunt reactor connected at the end of a long EHV line? A. To limit short-circuit current at the generator B. To absorb charging current and limit receiving-end voltage rise (Ferranti effect) C. To increase the line charging current D. To reduce mechanical forces in generator windings Answer: B. On long lightly loaded lines surplus VAr raises the receiving-end voltage; the shunt reactor absorbs it. (Key point: Shunt reactor) ## Related in Power Plant Equipment - [Function of reactor in power system](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Areactor-function) — Power Plant Equipment, chapter 4, asked 3× - [Reactors in stations: merits and demerits](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Areactors-merits-demerits) — Power Plant Equipment, chapter 4 - [Reactor schemes in stations and substations](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Areactor-schemes) — Power Plant Equipment, chapter 4 - [Reactor function and ring bus-bar scheme](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Aring-bus-reactor-scheme) — Power Plant Equipment, chapter 4 - [Reactor to protect circuit breaker of small station](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Areactor-protect-circuit-breaker) — Power Plant Equipment, chapter 4 - [Fire fighting system in power station](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Afire-fighting-power-station) — Power Plant Equipment, chapter 4, asked 5× ## Related in other subjects - [Generator-reactor system fault MVA](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Agenerator-reactor-fault-mva) — Power System Analysis II, chapter 3 - [Completely mixed ASP reactor, 10,000 m³/day](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Aasp-completely-mixed-10000) — Sanitary Engineering, chapter 7 - [Shunt reactors for 750 kV line ABCD](https://www.bctengineer.com/question.md?key=semester_8%2Fhigh_voltage_engineering%3Ashunt-reactor-abcd-750kv) — High Voltage Engineering, chapter 3 - [Distribution system used in INPS](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Ainps-distribution-system-type) — Transmission and Distribution System Design, chapter 5