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T/F: conductor configuration for 400 kV lines

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.

State and justify whether the following statement is TRUE or FALSE: Vertical configuration is generally adopted for transmission line of above 400 kV.

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.

✓ Answer checked by Claude Opus 5.5 (high effort)

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