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T/F: tower height independent of span

Short answer

FALSE. Maximum sag grows with the square of span length, requiring taller towers for longer spans to maintain ground clearance. Tower height thus directly depends on span.

State whether the following statement is TRUE or FALSE. Justify your answer with a brief explanation: The height of a tower is independent of span length of the transmission line.

FALSE.

The tower height is

Ht=hg+Smax+(vertical spacing between conductors)+hewH_t = h_g + S_{max} + \text{(vertical spacing between conductors)} + h_{ew}

The maximum sag at mid-span between supports at equal level is

Smax=w L28TS_{max} = \frac{w\,L^2}{8T}

It grows with the square of the span LL. A longer span therefore needs a taller tower to keep the same minimum ground clearance.

For example, if the sag is 3.1 m at a 250 m span, then at the same tension a 350 m span gives 3.1×(350/250)2≈6.13.1 \times (350/250)^2 \approx 6.1 m. The tower must then be about 3 m taller.

This is why fewer but taller and heavier towers are traded against more, shorter towers when finding the most economical span.

✓ Answer checked by Claude Opus 5.5 (high effort)

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