--- title: "Interconnected system SLD and functions of each part" subject: "Power System Analysis I" chapter: 1 key: "semester_4/power_system_analysis_i:interconnected-sld-functions" source: https://www.bctengineer.com/q/semester_4/power_system_analysis_i/interconnected-sld-functions site: BCT Engineering --- # Interconnected system SLD and functions of each part Power System Analysis I · Chapter 1: General Background - Asked in: 2076 Baisakh, 6 marks - Video: [Single Line Diagram of Power System | Explained | TheElectricalGuy](https://www.youtube.com/watch?v=gpbBhZcLrWs) — Gaurav J - TheElectricalGuy - 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/interconnected-sld-functions - Whole chapter: https://www.bctengineer.com/md/semester_4/power_system_analysis_i/chapter-1 ## Question Draw a single line diagram of an interconnected power system showing generation, transmission and distribution systems and describe the function of each system. ## Short answer Generation converts primary energy to electricity at11 kV. Transmission carries bulk power at132–400 kV from plants to load centers and interconnects grids. Distribution steps down voltage to11 kV and400/230 V and supplies consumers through primary and secondary networks. ## Answer #### Single line diagram ```text [G] 11 kV Step-up Transmission |---->[11/220 kV]====== 220/400 kV ======+ | [G] 11 kV [220/132 kV] |---->[11/132 kV]====== 132 kV ====== Grid S/S | Sub-transmission 66/33 kV | [33/11 kV] S/S | Primary distribution 11 kV | [11/0.4 kV] DT | Secondary 400/230 V consumers ``` #### Function of each system **1. Generation system** - Converts primary energy (water, fuel, sun) into electrical energy in power stations at 6.6–11 kV. - Includes turbines, alternators, exciters, governors and step-up transformers. - Controls frequency (through governors) and voltage (through AVR). **2. Transmission system** - Carries bulk power from generating stations to major load centres at extra-high voltage (400, 220, 132 kV in Nepal). - Interconnects power stations and neighbouring grids, allowing power exchange, sharing of reserve and economic dispatch. - Includes towers, conductors, insulators, grid substations and protection. - High voltage reduces current, losses and conductor cost. **Sub-transmission** (66/33 kV) links grid substations to distribution substations in cities and districts. **3. Distribution system** - Delivers power from distribution substations (33/11 kV) to individual consumers. - **Primary distribution** at 11 kV feeds distribution transformers and bulk consumers. - **Secondary distribution** at 400 V (3-phase) / 230 V (1-phase) supplies houses, shops and small industries. - Includes feeders, distributors, service mains, distribution transformers and meters. | System | Voltage | Main function | |---|---|---| | Generation | 11 kV | Produce power | | Transmission | 132–400 kV | Bulk transfer, interconnection | | Sub-transmission | 33–66 kV | Feed local substations | | Distribution | 11 kV, 400/230 V | Supply consumers | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is a function of the generation system? A. Deliver power to houses B. Carry bulk power at 400 kV C. Convert primary energy to electricity at 6.6-11 kV and control f and V D. Step 11 kV to 400 V Answer: C. Governors control frequency and AVR controls voltage. (Key point: Generation) 2. What is a main benefit of high-voltage transmission? A. Higher current B. Safer for consumers C. Eliminates substations D. Lower current, losses and conductor cost Answer: D. High voltage reduces current. (Key point: Transmission) 3. What does sub-transmission do? A. Links grid substations to distribution substations at 66/33 kV B. Generates power C. Feeds houses at 230 V D. Interconnects countries at 400 kV Answer: A. It is the intermediate level. (Key point: Sub-transmission) 4. Secondary distribution voltage is? A. 11 kV B. 400 V three-phase / 230 V single-phase C. 33 kV D. 132 kV Answer: B. Primary is 11 kV; secondary feeds houses and shops at 400/230 V. (Key point: Primary vs secondary) ## Related in Power System Analysis I - [Interconnected system SLD with bus voltages](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Ainterconnected-sld-bus-voltages) — Power System Analysis I, chapter 1 - [Interconnected system SLD, isolated vs interconnected, advantages](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Ainterconnected-sld-isolated-advantages) — Power System Analysis I, chapter 1 - [SLD of interconnected system vs isolated system](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Ainterconnected-sld-vs-isolated) — Power System Analysis I, chapter 1 - [SLD with voltage levels and why three-phase](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Asld-voltage-levels-three-phase) — Power System Analysis I, chapter 1 - [Single line diagram and its significance](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Asingle-line-diagram-significance) — Power System Analysis I, chapter 3 - [Interconnected power system and advantages](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Ainterconnected-system-advantages) — Power System Analysis I, chapter 1 ## Related in other subjects - [Distribution substation with single line diagram](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Asld-distribution-substation) — Industrial Power Distribution and Illumination, chapter 4 - [Interconnected system and transmission planning](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Ainterconnected-system-planning) — Transmission and Distribution System Design, chapter 1 - [Advantages of interconnected power system](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Ainterconnection-advantages) — Power System Analysis II, chapter 1, asked 3× - [Real power/frequency control in interconnected system](https://www.bctengineer.com/question.md?key=semester_5%2Fpower_system_analysis_ii%3Areal-power-frequency-control) — Power System Analysis II, chapter 1