--- title: "T/F: conductor configuration for 400 kV lines" subject: "Transmission and Distribution System Design" chapter: 4 key: "semester_8/transmission_and_distribution_system_design:tf-vertical-configuration-400kv" source: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/tf-vertical-configuration-400kv site: BCT Engineering --- # T/F: conductor configuration for 400 kV lines Transmission and Distribution System Design · Chapter 4: Conductor and Support Selection - Asked in: 2078 Chaitra, 1+3 marks; 2073 Bhadra, 4 marks (asked 2 times) - 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-vertical-configuration-400kv - Whole chapter: https://www.bctengineer.com/md/semester_8/transmission_and_distribution_system_design/chapter-4 ## Question State and justify whether the following statement is TRUE or FALSE: Vertical configuration is generally adopted for transmission line of above 400 kV. ## Short answer FALSE. For single-circuit lines above 400 kV, horizontal configuration is generally adopted because it gives lower tower height, better shielding with two earth wires, reduced overturning moment, and avoids phase-to-phase contact during ice shedding. Vertical configuration is typical for double-circuit lines up to 220 kV. ## Answer **FALSE.** For lines of 400 kV and above, the **horizontal configuration** is generally adopted for single-circuit lines. The vertical configuration is used for double-circuit lines up to 220 kV, and occasionally for 400 kV double circuits. Reasons for the horizontal configuration at EHV: 1. **Lower tower height:** all phases are on one level. A vertical arrangement would stack three large phase spacings (8–12 m each) plus long strings, making the tower very tall and heavy. 2. **Smaller overturning moment:** the conductors are lower, so the moment from wind is less and the foundations are cheaper. 3. **Lightning performance:** low conductors and two earth wires give better shielding and fewer strikes. 4. **Galloping and ice shedding:** with no conductor directly above another, a conductor jumping after ice shedding cannot clash with the phase above. 5. **Maintenance:** the lower height makes stringing and live-line work easier. The disadvantage is a wider right-of-way. Where land is costly, a vertical or delta double-circuit tower is chosen instead. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Vertical configuration is generally adopted for lines above 400 kV. This is: A. True, to save right-of-way B. True, because it gives better lightning shielding C. False, horizontal configuration is generally used for single circuit EHV lines D. False, delta is always used Answer: C. Horizontal configuration is generally used at 400 kV and above. (Key point: Verdict) 2. Why does a vertical arrangement suit EHV badly? A. It makes the phase spacing smaller B. Three large phase spacings (8-12 m each) are stacked, making the tower very tall and heavy C. It increases the corona D. It requires no earth wire Answer: B. Large EHV spacings stacked vertically give a very tall, heavy tower. (Key point: Tower height) 3. What is the main disadvantage of the horizontal configuration? A. Higher overturning moment B. More lightning strikes C. Wider right-of-way D. Conductor clashing after ice shedding Answer: C. A horizontal layout needs more width, hence a wider right-of-way. 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