--- title: "Reactors in stations: merits and demerits" subject: "Power Plant Equipment" chapter: 4 key: "semester_7/power_plant_equipment:reactors-merits-demerits" source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/reactors-merits-demerits site: BCT Engineering --- # Reactors in stations: merits and demerits Power Plant Equipment · Chapter 4: Substation Equipments - Asked in: 2072 Kartik, 8 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/power_plant_equipment/reactors-merits-demerits - Whole chapter: https://www.bctengineer.com/md/semester_7/power_plant_equipment/chapter-4 ## Question Explain reactors used in generating stations and substations with diagram. Also discuss their merits and demerits along with field of application. ## Short answer Generator reactors limit generator fault current but cause constant drop and loss. Feeder reactors protect individual feeders and keep bus voltage up, but not bus faults, and cause feeder loss. Bus-bar reactors (ring or tie-bar) have low normal loss and confine faults to sections; tie-bar adds extra bus and unbalanced-section voltage differences. Generator reactors are rarely used, feeder reactors suit distribution substations, bus-bar reactors suit large stations. ## Answer A **reactor** is an inductive coil with high reactance and negligible resistance. In generating stations and substations it is used to **limit short-circuit current**, localise faults, and keep bus voltage up on healthy sections. Air-core (dry, concrete-supported) reactors are common because their reactance does not fall by saturation at high fault current. #### 1. Generator reactors ```text G1 G2 G3 | | | [X] [X] [X] | | | =+=======+=======+=== bus | | feeders ``` - **Merits:** protects each generator from heavy fault current; useful for old machines with low reactance. - **Demerits:** always carries full load current, so constant voltage drop and $I^2R$ loss; a bus or feeder fault still affects all generators; gives no protection between feeders. - **Application:** rarely used now, since modern generators have enough leakage reactance. #### 2. Feeder reactors ```text G1 G2 | | =+===+===+===+=== bus | | [X] [X] | | feeder1 feeder2 ``` - **Merits:** a fault on one feeder hardly affects bus voltage, so other feeders keep supplying; breaker ratings of feeders reduced. - **Demerits:** no protection for bus-bar faults; constant drop and loss on every feeder; poor regulation. - **Application:** distribution substations with many radial feeders. #### 3. Bus-bar reactors (a) **Ring system** ```text G1 G2 G3 | | | =S1===[X]===S2===[X]===S3= | | +----------[X]-----------+ ``` (b) **Tie-bar system** ```text G1 G2 G3 | | | =S1= =S2= =S3= sections | | | [X] [X] [X] | | | =+=======+=======+= tie-bar ``` - **Merits:** in normal operation little current flows through bus reactors, so loss and drop are small; a fault is confined to one section; tie-bar system lets sections be added easily, and fault current from other sections passes through two reactors in series. - **Demerits:** a fault on a section gets full fault current from its own generator; tie-bar needs an extra bus; large voltage difference between sections if loads are unbalanced. - **Application:** large generating stations with several sections and many generators. #### Summary | Scheme | Normal loss | Main protection | |---|---|---| | Generator reactor | High | Limits each generator's fault current | | Feeder reactor | High | Limits feeder-fault current; keeps bus voltage up | | Bus-bar (ring/tie-bar) | Low | Confines a fault to one section | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the main demerit of generator reactors? A. They carry no current in normal operation B. They always carry full load current, causing constant voltage drop and I^2R loss C. They cannot protect the generator D. They need an extra tie-bar Answer: B. Being in series with each generator, they carry load current all the time, so there is constant drop and loss. (Key point: Generator reactor demerit) 2. Where are feeder reactors mainly applied, and what is their merit? A. Large stations with many generators; protects bus faults B. Distribution substations with many radial feeders; a feeder fault hardly affects bus voltage C. Old low-reactance generators; confines faults to one section D. Long EHV lines; absorbs charging current Answer: B. Feeder reactors keep the bus voltage nearly normal on a feeder fault, so other feeders keep supplying; they suit radial distribution. (Key point: Feeder reactor application and merit) 3. Why do bus-bar reactors have low normal-operation loss? A. They are short-circuited by a switch B. Little current flows between sections in normal operation C. They use superconducting coils D. They are in series with each load Answer: B. Sections are self-supplied by their own generators, so very little current passes through the bus reactors normally. (Key point: Bus-bar reactor merit) 4. Which statement about the tie-bar system is correct? A. It needs no additional bus B. Fault current from another section passes through two reactors in series C. Fault current from another section passes through only one reactor D. Sections cannot be added easily Answer: B. Each section connects to the tie-bar through its own reactor, so current from another section crosses two reactors; it needs an extra bus. (Key point: Tie-bar system) ## Related in Power Plant Equipment - [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 - [Why reactors are used and their types](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Areactor-types) — Power Plant Equipment, chapter 4 - [Combined cycle merits, demerits and designs](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Acombined-merits-designs) — Power Plant Equipment, chapter 8, asked 2× ## Related in other subjects - [Incineration: merits and demerits](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Asolid-waste-incineration) — Sanitary Engineering, chapter 10, asked 7× - [Three pipe materials with merits/demerits](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Apipe-materials-merits-demerits) — Water Supply Engineering, chapter 8, asked 4× - [Sewer pipe materials: merits, demerits](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Asewer-pipe-materials) — Sanitary Engineering, chapter 3 - [Cofferdam types, uses, merits and demerits](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Acofferdam-types-merits) — Foundation Engineering, chapter 5, asked 7×