Selecting Pole Positions and Pole Top Construction For MV Line

Selecting Pole Positions and Pole Top Construction For MV Line

For pole positioning guidelines.

Firstly, position poles along the route at any key or constrained locations.

Next determine the maximum span length that can be achieved over flat ground given the attachment heights on poles, the sag at the nominated stringing tension and the required ground clearance. Also check the spanning capability of the pole top constructions to be used. Position poles along the route so that this spacing is not exceeded. If there are gullies between poles, the spacing can be increased and if there are 'humps' mid-span, span lengths can be reduced.

Strain Points, Pole Details and Pole Top Constructions have to be determined. Strain point locations need to be determined:

1) To isolate electrically different circuits.

2) To keep very short spans or very long spans mechanically separate, such that all spans in a strain section are of similar length (no span less than half or more than double the ruling span length, and on tight-strung lines, the longest span not more than double the shortest span). Failure to limit span variance can cause excess sagging in longest span at higher design temperature loadings.

3) To isolate critical spans, e.g. spans over a river, major highway or railway line, to help facilitate repairs or maintenance.

4) On line deviation angles too great for intermediate constructions, e.g. Cross-arms with pin insulators.

5) At locations where there are uplift forces on poles.

6) At intervals of approximately 10 spans or so.

The following points also must be considered:

1) Strain section length limitation will be favorable if a line is affected by wires brought down in a storm. Also, the length of conductor on a drum may be a consideration.

2) Span lengths within the strain section must be reasonably similar and poles and pole top construction used must be reasonably consistent, as this gives the line a tidy appearance.

3) When nominating suitable pole top constructions for intermediate poles, adequate capacity must be available for the deviation angle at each site.

4) Pole strengths and foundation types/sinking depths must be nominated as a first pass, as these may need to be amended later once tip loads are determined. Stronger poles will be required at terminations and on large deviation angles. Pole sinking depths can be determined.