Route Survey and Ground Line Profile for MV Line Design

 Route Survey and Ground Line Profile for MV Line Design

A ‘line route survey’ is carried out to determine:

a) Details of existing electricity infrastructure;

b) Terrain and site features, e.g. trees, access tracks, fences, gullies; and

c) Ground line rise and fall along the route.

Ground line profiling may not be necessary for minor projects in urban areas where the ground is reasonably level or has a consistent slope throughout and there are no on site obstructions.

The designer can check worst case ground clearances by deducting the sag in the span from the height of the supports at either end by taking the following measurements:

a) Conductor temperature

b) Conductor size/type

c) Ambient temperature

d) Conductor attachment point with respect to ground level

e) Strain points

However, ground line profiling is essential where:

1) Poles have to be positioned along an undulating traverse;

2) There is a 'hump' or change in gradient in the ground at mid span;

3) Outside of urban areas where spans are comparatively long-say in excess of 80 m;

4) The designer has doubts about the adequacy of required clearances; and

5) Where uplift on poles is suspected.

The equipment used to obtain measurements will depend on the complexity of the project. For many distribution lines, a simple electronic distance measuring device and inclinometer are adequate. Elsewhere, use of a high end GPS unit or LiDAR may be warranted. The route is broken up into segments, typically corresponding with 'knee points' or changes in gradient. Slope distance and inclination measurements for each segment can be converted to chainage and reduced level (RL) values to facilitate plotting as follows:

Software packages can be used to plot survey data. Apart from the ground line, various features and stations must be shown, including existing poles, gullies, fences, obstacles, roadways. A clearance line is then drawn offset from the ground line, according to the minimum vertical clearances that apply.