33 kV steel mast lines in the UK
Contents
Overview
Placing 33 kV lines on steel supports in the UK was common practice in the UK up to the 1940s. Following World War II, wood pole construction became standard. Steel supports were typically lattice towers (“pylons”), but other steel supports were also used.
Support types include:
- Lattice towers
- Steel girders: the so-called “Woodhouse masts” (used at 11, 33 and 66 kV)
- Lattice masts, such as those from Painter Brothers
Painter Brothers
Painter Brothers’ “Painter’s Universal” poles (“PU” poles) were internally-braced pairs of steel channels. These were used singly for both 11 and 33 kV lines, all single circuit. Examples are given on the Painter Brothers page.
South Scotland
A somewhat similar lattice mast design was used in South Scotland for 33 kV lines under what Tom Gloag’s research suggests is SS SL2 (South Scotland Secondary Line contract 2), which may make it (presumably depending on the region) a Watsham’s or a General Electric Co. design. The angled crossarms are of a very similar design to one of the Painter Brothers lines found near Edinburgh. Unlike other types, the intermediate masts are tapered instead of parallel.
[Marshall] (1933) illustrates the single-circuit line mast, giving a mast height of 35′–3″. An example of such a mast can be seen at the link below. Thus far, no double-circuit masts have been seen.
The mast types are said to be 0°, 8°, 24°, 60° and a “T” type, in single and double circuit. The standard span was 450 feet, and the conductor used was 0.075 square inch copper-equivalent.
Examples:
- Line mast, Yetholm (Geograph Britain and Ireland)
North Wales
There is a double-circuit 33 kV line between Colwyn Bay and Llandudno constructed using lattice masts similar to those found in South Scotland. The crossarms are simple bars bearing small pin insulators on each end. Towers are used for deviation. Currently there don’t seem to be any photographs outside of Google Street View.
Lydney
Single-circuit lattice masts exist in Lydney and other parts of Gloucestershire of a very strange design. The intermediate masts have tension insulator strings instead of the pin insulators used in South Scotland. One side has two crossarms that have enough clearance for 33 kV at 45° wind swing, while the opposite side has a distinctly shorter crossarm that looks like it would struggle to provide sufficient clearance. In still air, there is plenty of space for 66 kV, but this would not be tenable in high winds. At present the insulator strings are two-unit, indicating 11 kV; however, there is also a line of towers insulated to 66 kV and de-rated to 33 kV, so one cannot be certain about what the masts were originally designed to support. The suggestion is that they are for 11 kV only, with sufficient vertical spacing for longer spans.
The masts do not support an earthwire.