Spey Valley Extension

Contents

• Overview
  • General data
• Lines
• Tower forms
  • Original design
  • 132 kV double circuit uprating
• Tower details
• Examples
  • Newtonmore
• See also

Overview

The Spey Valley Extension (Tummel–Keith line) was a 120 mile 132/33 kV dual-voltage power line constructed by Balfour Beatty ca. 1936–1939 between Tummel Bridge and Keith in Scotland, on behalf of the Grampian Electricity Supply Company. The towers were designed by Blaw Knox as contract K1576, with 132 kV crossarms on the west side and short 33 kV crossarms on the east side. The tower suite appears to be specific to this line and not used for any other contracts. Perhaps due to the superficial similarity to SEE PL1a towers, there is a long-standing misconception that Pirelli designed the Spey Valley towers, but this is not true.

The minutes from the Scottish Power Company’s 1937 Annual General Meeting indicate that the 85-mile line from Tummel Bridge to Keith was completed around 1936/37 but other sources are alleged to give 1939 as the year of commissioning. Curiously, the northern end of the line is missing from the 1945–47 Ordnance Survey one-inch map of Scotland; some of the mapping may have been pre-war and pre-dating the line’s construction.

At some point after 1990, the section from Errochty Switching Station at Tummel Bridge to Etteridge was reconfigured to be 132 kV double circuit, with replacement crossarms fitted accordingly. Etteridge, which is around four miles from Newtonmore, is where the line was teed out to Fort Augustus substation in the 1950s.

All of the line south of Boat of Garten is now gone (as is the 132 kV line to Fort Augustus), and Open Infrastructure Map indicates that the 33 kV side of the line from Keith to Speybridge is de-energised, with only Speybridge to Boat of Garten substation still being 132/33 kV. Most of the line from Speybridge to Boat of Garten is now undergrounded as part of SSEN’s Ofgem-funded VISTA (Visual Impact of Scottish Transmission Assets) scheme to improve the visual quality of the natural landscape.

Prior to its demolition, sections of the line between Boat of Garten and Tummel Bridge used J L Eve 0.175 towers due to road alterations.

General data

Contractor	Blaw Knox
Found
Height (straight line tower)	81′–4″ (24.8 m)
Voltage	132 + 33 kV (two circuit dual voltage)
Known conductors	Single
Design conductor	?
Design earthwire	?
Circuit count	2 × single circuit

Lines

• Spey Valley Extension: Tummel Bridge/Errochty Switching Station to Keith, now reduced to Keith to Speybridge

Tower forms

The diagrams below are shown to scale at 12 pixels per metre.

Certain details are derived solely from Google Street View. These are the “spires” fitted to selected towers, and the short peaks found on various angle towers. The “spire” towers also have different top crossarms to the standard towers. Google Street View clearly shows that some angle towers have shorter peaks, but the apparent height of the peak varies between examples and it’s impossible to be certain on the dimensions.

Lightning rods, not shown here, are fitted to some towers, just as they were with Rannoch–Abernethy towers and Blaw Knox K1373.

Presumably because they are dual-voltage, the towers use Blaw Knox’s special designations of S, M and D. The suspension tower is designated “S”. Examination of the route of the line suggests that the M angle tower is 20° deviation, with the D angle tower most likely being 60°. No details are known about the original terminal towers; at the Keith end, the last two towers are now PL16 DD30 and DDT90, types which did not exist when the line was originally constructed.

Original design

The line tower is taller than typical first generation towers, standing at 81′–4″ (24.8 m), but the angle towers used standard first generation clearances: 44 feet to the bottom crossarm and 12 feet between crossarms.

132 kV double circuit uprating

In the 1990s, Tummel Bridge to Etteridge was uprated to double circuit 132/132 kV. In most cases this resulted in symmetrical towers. However, the new 132 kV crossarms on the transposition towers—replacing the 33 kV crossarms—were a different design to the original 132 kV crossarms. This entire section has now been demolished as part of the rationalisation and upgrade of the power grid, for which the Beauly–Denny line is the overall replacement, built using the new SSE400 400 kV towers.

Tower details

Overall width is the total width across the widest crossarm, taken to the conductor attachment points rather than to the end of the steelwork. Overall width for the uprated towers is based on the assumption that the new 132 kV crossarms (replacing the 33 kV crossarms) are the same length as the original 132 kV crossarms; this appears to be the case for all towers except for transposition.

Examples

Newtonmore

Photos taken by Ian McAulay from the side of the A9 outside of Newtonmore. This part of the line remained dual voltage. This location is a little north of the tee at Etteridge that led to Fort Augustus. This section of line was demolished around 2015. The photos were taken in May 2006.

See also

• Line tower, 132 kV double circuit (Flickr)
• Angle tower, 132 kV double circuit (Flickr)
• 132/132 kV towers near Dalwhinnie (Alamy)
• Old and new towers, new tower awaiting stringing (Flickr)
• Energy giant faces prosecution over noise from new power line — article in the Herald which shows a photo of the old towers