--- title: "T/F: lightning overvoltage in distribution system" subject: "Transmission and Distribution System Design" chapter: 3 key: "semester_8/transmission_and_distribution_system_design:tf-lightning-distribution-vs-transmission" source: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/tf-lightning-distribution-vs-transmission site: BCT Engineering --- # T/F: lightning overvoltage in distribution system Transmission and Distribution System Design · Chapter 3: Overhead Line Insulator Design - Asked in: 2080 Chaitra, 4 marks - 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/tf-lightning-distribution-vs-transmission - Whole chapter: https://www.bctengineer.com/md/semester_8/transmission_and_distribution_system_design/chapter-3 ## Question State whether the following statement is TRUE or FALSE and justify your answer with brief explanation: Lightning over voltage is more dominating in distribution system than in transmission system. ## Short answer TRUE. Distribution lines have low BIL and no shield wire, so even induced surges cause flashover. Transmission lines have higher BIL, shield wires, and low tower footing resistance; lightning is dominant only up to about 220 kV, while switching surges govern at higher voltages. ## Answer **TRUE.** - Distribution lines (11 kV, 33 kV) have low insulation levels (BIL about 75–200 kV). Even an **induced surge** from a nearby lightning stroke (100–300 kV) is enough to flash them over; direct strokes always do. - They usually have no overhead shield wire, short and low poles, and run through open areas where many strokes occur. - Transmission lines have high BIL (550–1550 kV), shield (earth) wires and low tower footing resistance, so most strokes are intercepted and induced surges are harmless. - In EHV lines (400 kV and above) the insulation is governed mainly by **switching surges**, not lightning. Hence lightning is the dominant over-voltage for distribution systems, while switching surges become dominant as transmission voltage increases. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Is lightning over-voltage more dominating in distribution than in transmission? A. True B. False C. True only at 400 kV D. False because distribution has shield wires Answer: A. Distribution has low BIL and little shielding, so lightning dominates; at EHV switching dominates. (Key point: Verdict) 2. Why can induced surges flash over distribution lines? A. Induced surge of 100-300 kV exceeds BIL of 75-200 kV B. BIL is above 1500 kV C. They have earth wires D. Footing resistance is zero Answer: A. Distribution BIL is low, so even nearby strokes cause flashover. (Key point: Induced surges) 3. What protects transmission lines from lightning? A. Isolated neutral B. Shield (earth) wires, high BIL and low footing resistance C. Higher SSR D. Thinner conductors Answer: B. Most strokes are intercepted by shield wires, and the high BIL withstands the rest. (Key point: Transmission protection) ## Related in Transmission and Distribution System Design - [T/F: radial more reliable than network](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-radial-more-reliable-network) — Transmission and Distribution System Design, chapter 5, asked 2× - [T/F: more circuits rather than higher voltage](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-circuits-rather-than-voltage) — Transmission and Distribution System Design, chapter 2 - [T/F: higher voltage more economical](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-higher-voltage-more-economical) — Transmission and Distribution System Design, chapter 2 - [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 - [T/F: X/R ratio, transmission vs distribution](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-xr-ratio-transmission-distribution) — Transmission and Distribution System Design, chapter 1 - [T/F: temporary vs transient overvoltage](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-temporary-vs-transient-overvoltage) — Transmission and Distribution System Design, chapter 3 ## Related in other subjects - [True/false: cables suppress switching overvoltage](https://www.bctengineer.com/question.md?key=semester_8%2Fhigh_voltage_engineering%3Atf-underground-cables-switching) — High Voltage Engineering, chapter 3 - [True/false: load rejection raises terminal voltage](https://www.bctengineer.com/question.md?key=semester_8%2Fhigh_voltage_engineering%3Atf-load-rejection-voltage-rise) — High Voltage Engineering, chapter 3 - [When terminal voltage is less or more than emf](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machines_ii%3Aterminal-voltage-less-or-more) — Electric Machines II, chapter 1 - [True/false: derivative controllers always used with others](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Aderivative-always-with-others) — Control Systems, chapter 7, asked 3×