--- title: "Merits and demerits of grid connected system" subject: "Transmission and Distribution System Design" chapter: 1 key: "semester_8/transmission_and_distribution_system_design:grid-connected-merits-demerits" source: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/grid-connected-merits-demerits site: BCT Engineering --- # Merits and demerits of grid connected system Transmission and Distribution System Design · Chapter 1: Introduction - Asked in: 2070 Magh, 6 marks - Video: [interconnected grid system and its advantages and disadvantages | jitendra sah](https://www.youtube.com/watch?v=kMWhCeUgYz0) — jitendra sah - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/grid-connected-merits-demerits - Whole chapter: https://www.bctengineer.com/md/semester_8/transmission_and_distribution_system_design/chapter-1 ## Question Explain the merits & demerits of grid connected power system. ## Short answer Merits: high reliability, reduced reserve, economic dispatch, load diversity, better frequency/voltage stability, energy trade. Demerits: higher fault levels, cascade blackout risk, complex control and protection, inter-area oscillations, tie-line cost, and strict grid codes for small plants. ## Answer A **grid-connected power system** is one in which generating stations and loads of different regions are connected through a common transmission network (the grid) and operated together, e.g. the Integrated Nepal Power System (INPS) under NEA. #### Merits 1. **Reliability of supply:** loss of one plant or line is covered by other sources through alternative paths. 2. **Reduced reserve capacity:** reserve is shared among all plants. 3. **Economic operation:** cheapest plants (run-of-river hydro) are loaded first; costly diesel/thermal used only at peak. 4. **Diversity benefit:** regional peaks occur at different times, so required installed capacity is lower. 5. **Better frequency and voltage stability:** large total inertia and high fault level make the system stiff. 6. **Optimal use of hydro:** surplus monsoon energy can be exported (e.g. to India) and dry-season deficits imported. 7. **Allows larger, more efficient generating units** and integration of distributed and renewable plants. #### Demerits 1. **Higher fault level,** needing breakers of higher rupturing capacity. 2. **Cascade tripping:** a severe fault may spread and cause a nation-wide blackout. 3. **Complex control and protection:** load-frequency control, tie-line control, scheduling and SCADA are required. 4. **Stability issues** on long weak tie lines (inter-area oscillations). 5. **High capital cost** of transmission lines, substations and communication. 6. Small plants must follow strict grid code rules (frequency, voltage, protection settings). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How does grid operation give economic benefit? A. Costly diesel plants run first B. Cheapest plants such as run-of-river hydro are loaded first C. All plants share load equally D. Only thermal plants operate Answer: B. Cheap plants are used fully; costly ones only at peak. (Key point: Economic operation) 2. Why is a grid 'stiff' with better frequency and voltage stability? A. Low inertia B. Large total inertia and high fault level C. No loads D. Series reactors everywhere Answer: B. Large inertia and high SCMVA resist disturbances. (Key point: Stiff grid) 3. A drawback of grid connection related to breakers is: A. Lower fault level needs smaller breakers B. Higher fault level needs breakers of higher rupturing capacity C. Breakers are not needed D. Fault level is unchanged Answer: B. Interconnection raises SCMVA so breakers need higher rating. (Key point: Demerit: fault level) 4. A severe fault in a grid may: A. Never spread B. Spread by cascade tripping and cause a wide blackout C. Improve reliability D. Reduce frequency control needs Answer: B. Cascade tripping can cause nation-wide blackout. (Key point: Cascade) ## Related in Transmission and Distribution System Design - [T/F: grid connected system more stable](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-grid-connected-more-stable) — Transmission and Distribution System Design, chapter 1 - [Radial, loop and network distribution merits](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Aradial-loop-network-merits) — Transmission and Distribution System Design, chapter 5 - [Voltage and circuits for 250 MW grid connection](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Avoltage-circuits-250mw-grid-options) — Transmission and Distribution System Design, chapter 2 - [Voltage, circuits and discs for 260 MW grid link](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Avoltage-circuits-260mw-grid-options) — Transmission and Distribution System Design, chapter 2 - [Voltage and circuits for 180 MW grid link](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Avoltage-circuits-180mw-grid-options) — Transmission and Distribution System Design, chapter 2 ## Related in other subjects - [Merits and demerits of interconnected system](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Ainterconnection-merits-demerits) — Power System Analysis II, chapter 1, asked 3× - [Distribution layouts, merits and demerits](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Adistribution-layouts-merits-demerits) — Water Supply Engineering, chapter 7, asked 6× - [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 - [Merits and demerits of DC track electrification](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Adc-track-electrification-merits) — Utilization of Electrical Energy, chapter 4