--- title: "Advantages of solidly grounded generators" subject: "Power Plant Design" chapter: 4 key: "semester_8/power_plant_design:solidly-grounded-advantages" source: https://www.bctengineer.com/q/semester_8/power_plant_design/solidly-grounded-advantages site: BCT Engineering --- # Advantages of solidly grounded generators Power Plant Design · Chapter 4: Electric System Design of a Power Plant - Asked in: 2078 Chaitra, 4 marks - Video: [Neutral Grounding - Power System Earthing - Power System Engineering 1](https://www.youtube.com/watch?v=0K8pr8P-Aj0) — Ekeeda - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/power_plant_design/solidly-grounded-advantages - Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-4 ## Question Discuss advantages of solidly grounded system of generator grounding. ## Short answer Solid grounding holds neutral at earth potential, so healthy phases stay at phase voltage and arcing overvoltages are eliminated. Insulation can be graded for phase voltage. Protection is simple with reliable earth-fault relays, and LV four-wire loads are possible. The method is cheap and needs no additional impedance. ## Answer In **solid grounding**, the generator neutral is connected directly to the station earth with no intentional impedance. #### Advantages - **Neutral held at earth potential:** during a line-to-ground fault the healthy phases stay close to phase voltage, so there are no high overvoltages. - **No arcing-ground problem:** the fault current is large and the arc does not restrike, so transient overvoltages are eliminated. - **Reduced insulation cost:** equipment and lightning arresters can be rated for phase voltage (about 80 % arresters). - **Simple and reliable protection:** the large earth-fault current operates ordinary overcurrent/earth-fault relays quickly and selectively. - **Simple and cheap:** no resistor, reactor or transformer to buy and maintain. - **Supports single-phase loads:** a 4-wire LV supply (phase-to-neutral loads) is possible, which is why small LV diesel and micro-hydro sets are usually solidly grounded. - Better **personnel safety** because faults are cleared quickly. #### Limitation For large generators the earth-fault current can exceed the 3-phase fault current (since $X_0$ is small), causing stator core burning and severe mechanical stress, so solid grounding is used mainly on small LV machines. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why are overvoltages avoided in solid grounding? A. Neutral floats B. Resistor damps C. Fault current is small D. Neutral held at earth potential keeps healthy phases near phase voltage Answer: D. Fixed neutral prevents voltage shift in a line-to-ground fault. (Key point: Neutral potential) 2. Why is arcing ground not a problem in solid grounding? A. Arc is capacitive B. Fuses are used C. Large fault current prevents arc restriking D. Fault current is tiny Answer: C. The large current clears the fault, eliminating transient overvoltages. (Key point: Arcing) 3. Why is protection simple with solid grounding? A. Needs voltage relays B. Currents are small C. Large earth-fault current operates ordinary relays selectively D. Needs resonance tuning Answer: C. High current gives clear relay operation. (Key point: Protection) 4. Why is solid grounding used mainly on small machines? A. It costs more B. It needs a resistor C. It cannot supply single-phase loads D. Earth-fault current can exceed three-phase value, burning core Answer: D. X0 is small, so large fault current damages stator core in big generators. (Key point: Limitation) ## Related in Power Plant Design - [Types of generator neutral grounding](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Agenerator-neutral-grounding-types) — Power Plant Design, chapter 4 - [Grounded versus ungrounded systems](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Agrounded-vs-ungrounded) — Power Plant Design, chapter 4 - [Design: 245 m head plant, standby generator](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Adesign-2073-245m-standby) — Power Plant Design, chapter 4, asked 14× - [Design: 260 m head plant, generator lead](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Adesign-2078-260m-generator-lead) — Power Plant Design, chapter 4, asked 5× - [Generator choice and SCR versus stability](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Agenerator-choice-scr-stability) — Power Plant Design, chapter 4 - [Speed governing of a hydro generator](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aspeed-governing-hydro) — Power Plant Design, chapter 4 ## Related in other subjects - [Per unit circuit of three-generator system, 30 MVA base](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Apu-circuit-30mva-g1-g2-g3) — Power System Analysis I, chapter 3 - [Improper earthing and system grounding practice](https://www.bctengineer.com/question.md?key=semester_8%2Fhigh_voltage_engineering%3Aimproper-earthing-system-grounding) — High Voltage Engineering, chapter 2 - [Why and how the neutral is grounded](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Aneutral-grounding-methods) — Switchgear and Protection, chapter 5, asked 4× - [Line currents with isolated and grounded neutral](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Astar-impedance-unbalanced-voltages-neutral) — Power System Analysis II, chapter 4