Quoich to Broadford towers

Contents

• Overview
  • General data
• Tower forms
• Tower details
• Examples
  • Broadford

Overview

The line between Quoich Tee on the Scottish mainland and Broadford substation on the Isle of Skye uses a transmission tower type known only from this one line. The towers are Blaw Knox contract T2639, designed in 1975–1977; they are “light construction” towers, designed for 125 mm² Tiger SCA (ACSR) conductors. T2639 is a derivative of the Inveraray–Taynuilt type (Blaw Knox T1498), adapted to carry an earthwire. Being designed after the adoption of metric steel angles, the tower dimensions are still imperial (including the new earthwire peaks) but the bar sizes are metric.

The towers are all double circuit, but are strung single circuit only.

The Energy Voice article Maybe it’s time to look to Heligoland begins, “Current plans to reinforce the power line between Fort Augustus and the Western Isles, via Skye, reminded me of the controversy that arose when the link was created in the 1980s.” According to SSEN, the line was completed in 1980. [Skye reinforcement]

At present, there is a single circuit line on double circuit lattice towers between Quoich switching station and Broadford, followed by a Trident wood pole line to Ardmore substation via the Edinbane and Dunvegan substations. (It appears that Quoich was originally connected to Invergarry power station via a K1201 line, but at the intersection with Fort Augustus–Fort William the line currently diverts to Fort Augustus on wood poles; the line from Invergarry power station now tees into the line to Fort William.)

The tower types (except DT) have an “L” suffix, possibly to denote “light construction”.

General data

Designed for	NoSHEB (North of Scotland Hydro-Electric Board)
Design contract	Blaw Knox T2639
Found
Status	Historic, in service
Class	Light construction
Height (straight line tower)	73′–6″ (22.4 m)
Voltage	132 kV
Dates back to	1975, 1977 (drawings)
Known conductors	Single
Design conductor	125 mm² Tiger SCA
Design earthwire	60 mm² Skunk SCA
Circuit count	Double (strung single circuit)
Drawing ranges	T2639 / XM5379

Tower forms

Compared to their predecessor T1498, the T2639 towers exhibit a few changes. Most notable is the increased tower peak height. Perhaps unique in British tower design, the peak on the heavier angle towers is asymmetric about the transverse face to centre the earthwire across the phase conductors. Although some other types (most notably L7, L4(m) and L12) have projections to offset the earthwire position, this is the only known type with an asymmetric peak.

Possibly to accommodate the extra loading of the earthwire, the D2L and D10L towers have additional bracing compared to T1498. The bar sizes are not directly comparable between the two tower series as T1498 is imperial and T2639 is metric.

The following diagrams are shown to scale at 12 pixels per metre:

“SEC” here denotes “special earthwire clearance” and is an abbreviation created merely to maintain proper diagram spacing above.

The DT type appears to be simply a metricated PL16 DT90: the erection marks are the same as for K8323 SWE PL16 DT, with the customary “M” prefix to indicate metricated parts. There is no “L” suffix on the DT types. The Quoich DT tower is a junction tower and uses special auxiliary crossarms.

Tower details

Crossarm width is the total width across the widest crossarm pair. The tower outline dimensions are imperial, while the bar sizes are all metric.

* The distance between the top crossarm and the earthwire strain plate is 11 feet, but the tower peak is another five feet taller.

Examples

Broadford