SSE400

Contents
Overview
SSE400 is a UK electricity pylon (steel lattice transmission tower) series, seemingly now the joint tallest design in the UK alongside L6. This series was designed by Balfour Beatty for the 137 mile (220 km) Beauly–Denny power line in Scotland, built as one 400 kV circuit and one 275 kV circuit with both circuits being insulated for 400 kV. SSE400 is positioned as a standard design for future projects.
SSE400 is essentially a derivative of L12 with the extra strength required to handle the weather conditions in the Scottish highlands. SSEN claim that the Beauly–Denny line has the highest pylon in the UK, “located over 2,500ft up a mountain” (altitude or elevation of 762 m).
In [Coire Glas Connection], SSEN stated, “Standard height for 400kV design is 56 metres with a span of approximately 370 metres, around 30 – 35 Towers for 12 km.” This gives a span of around 1213 feet, approximately equal to the traditional 1200 foot span of imperial 275 and 400 kV towers. The documented height of SSE400 D STD is only 50.5 m, which is still four metres taller than L12 D STD at 46.5 m.
General data
Designer | Balfour Beatty |
---|---|
Found | |
Height (straight line tower) | 50.5 m |
Voltage | 400 kV |
Dates back to | ca. 2005 |
Conductors | Twin |
Circuit count | Double |
Design conductor | ? |
Design earthwire | ? |
Normal span | ca. 370 m |
Tower forms
The drawings below were manually traced from Balfour Beatty drawing A1/PTD/6054/223 ©2005 Balfour Beatty, which informs you that such an act is expressly forbidden! The crossarm lengths are taken to be to the centre of the crossarm attachment point. As with most such drawings, the crossarms were drawn as tapering to a point at these lengths. The conductor attachment bars have been added, and the crossarms truncated and capped.
The Beauly–Denny line is built with D55 as the highest permissible angle, with possibly only one D90, located between Fallin and Cowie, north of Denny. This one D90 is too far away to see clearly, but as L12 D90 appears to have all square-ended crossarms, SSE400 D90 is assumed to have the same. With the other exception being the DT, the remainder of the drawings have been adapted to match real-world towers.
At the Denny end of the line, L12X is claimed to have been used instead. Further inwards, such as around Buchanty, Gilmerton and Crieff, a lower strength version of the SSE400 D tower can be seen, which appears to simply be the D tower with reduced bracing. The designation of such towers is not known.
DL is the same tower as D but strengthened for an altitude of 650 metres.
The following diagrams are shown to scale at 12 pixels per metre:
Comparison with L12
Tower details
Crossarm width is the total width across the widest arms. For most of the towers the stated crossarm length is taken to be to the centre of the conductor attachment point rather than to the end of the steelwork, but this is not specified.
Type | Source | Height | Base width | Crossarm width |
---|---|---|---|---|
SSE400 D | A1/PTD/6054/223 | 50.5 m | 8.0 m | 21.7 m |
SSE400 DL | ||||
SSE400 D10 | 48.8 m | 9.9 m | 22.3 m | |
SSE400 D25 | 48.9 m | 10.8 m | 22.3 m | |
SSE400 D55 | 49.4 m | 13.5 m | 23.3 m | |
SSE400 D90 | 53.8 m | 15.5 m | 26.8 m | |
SSE400 DT | 56.4 m | 14.5 m | 31.9 m |