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SS-PL1

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Overview

Following on from their original tower design for the CS PL1 and SEE PL2 schemes, Milliken Brothers produced a new tower suite that went on to be used for most of the remaining PL1 schemes. [Standard Tower Types] uses the description “SS-PL1” for this type, although it appears that SS PL1 was not the first scheme to use these towers.

This “revised Milliken” type was used for CE PL1 (Central England), NWE PL1 (North West England and North Wales), NEE PL1 (North East England), SWE PL1 (South West England and South Wales), EE PL1 (East England) and SS PL1 (South Scotland). Mid-East England (MEE) and South East England (SEE) PL1 schemes used towers from Callender’s and GEC.

Although CS-PL1 and SS-PL1 are similar, there are some significant differences. The most notable one is that SS-PL1 added bracing to the peaks of the line towers (S2 and D2). SS-PL1 introduced much more robust 10° towers, using a design that appears to be from a completely different tower suite. The D30 tower was redesigned, with tighter X-bracing at the top of the tower and slimmer middle crossarms; the face bracing appears to have been removed from the middle crossarms.

General data

Design contractor Milliken Brothers
Found England Wales Scotland
Height (straight line tower) 66′–9″ (20.3 m) (SS PL1 S2)
79′–3″ (24.2 m) (EE PL1 D2)
Voltage 132 kV
Dates back to 1929–32 (drawings)
Known conductors Single
Circuit count Single, double

Custom S2 towers

At least two CEB regions used custom line towers on the single-circuit lines. In the SWE region, contract SWE PL1(a)&(b) used a custom Callender’s S2 tower alongside standard Milliken angle towers. In the CE region, at least one line used a Milliken design that was a forerunner to CE PL3 S2.

SS PL1 S2 (Milliken)
SWE PL1(a)&(b) S2 (Callender’s)
Stafford–Wolverhampton S2 (Milliken)
CE PL3 S2 SEW

The only drawings recovered for SWE PL1(a)&(b) are two for the S2, drawn in 1931. These towers can be seen on the lines between Castle Meads substation in Gloucester and Arlingham, and from Hayle substation to Fraddon substation. The angle towers on these lines all appear to be Milliken (specifically SWE PL1), suggesting that Callender’s only designed a replacement S2 tower.

The line between Stafford and Wolverhampton uses a Milliken type similar to CE PL3 S2, but with a wider base. Another tower of this type appears on the older line between Stourport and Bishops Wood substations. The pattern appears to be the same, but the line is too short to be certain.

Metrication

PL1(c)

PL1(c) is a metricated version of PL1. The only drawing obtained so far is BK35/27817 of unknown date, the GA&ED of the S10 STD tower. This drawing is from “PL1(c) : E141 TOWER SERIES”, where E141 is the Milliken/Blaw Knox contract number for SWE PL1.

There is a recently-constructed (between 2009 and 2015) PL1 ST outside Sleaford, providing a connection to the Sleaford Renewable Energy Power Station; this tower has been inserted into an MEE line formed of GEC towers. One would imagine that this new tower is PL1(c).

PL1(m)

[Standard Tower Types] includes “PL1(m)” as the replacement to SS-PL1 and CS-PL1, as well as “STL1” (K1420) and OL16 (folded plate single circuit). Presently the only metricated type known is PL1(c). Some examples described as “PL1(c)” may indeed be PL1(m).

Tower forms

Broadly, the tower designs should be essentially identical across all the revised Milliken schemes. Some differences do exist, in particular with the terminal towers. The diagrams below are not exhaustive with regards to schemes.

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

Single circuit towers

CE PL1 S2 (Milliken)
SS PL1 S2 (Milliken)
SS PL1 S10
PL1(c) S10
EE PL1 S30
EE PL1 S60
EE PL1 ST
SS PL1 ST (Glenlee etc)

Double circuit towers

EE PL1 D2
SWE PL1 D2
SWE PL1 D10
EE PL1 D30
NWE PL1 D30
EE PL1 D60
SWE PL1 D60
EE PL1 DT
SWE PL1 DT
SWE PL1 DT60
SWE PL1 DT60A
SWE PL1 DT-type Junction
EE PL1 DT90
CE PL1 LNE terminal
NWE PL1 transposition tower

On the basis that National Grid’s drawing register implies that DT90A is a DT90 with auxiliary crossarms, it would stand to reason that DT60A is a DT60 with auxiliary crossarms, which appears to be the case. DT60A also has all square-ended crossarms. The tower at Kendal has the square-ended crossarms but no auxiliary crossarms; its designation is not known. It may have been constructed this way to provide additional downlead take-off points.

The [Tower Bible] shows EE PL1 D30 without vertical bracing on the middle crossarm. Actual towers do have bracing just as with other SS-PL1 D30 towers, so the drawing above reflects this deviation. The EE PL1 D30 GA and ED drawings have not yet been recovered, but the tower bible is sufficiently accurate as to suggest that this was not a mistake.

There is a terminal tower at Worcester that is being taken to be one of the “LNE substation” terminal towers, covered under T161 (CE PL1) with no designation. Only the top of the tower can be seen on Street View and from an angle, but it appears to be a modified DT with a wide top crossarm (square-ended on one side) and a 6-foot peak. National Grid’s T161 drawing register describes these as “Terminal Towers for LNE Substations at Northampton, Worcester, Stafford and Stoke-on-Trent”; of these, only Worcester has a PL1 terminal tower left. Drawings for this type have yet to be recovered.

Suspension angle towers

Milliken PL1 is highly unusual within the UK in supporting 10° deviation using suspension towers. These towers have wider crossarms, presumably to provide the necessary clearance for the insulators to be pulled to one side, and the crossarms are more heavily braced to accommodate the higher loads.

This approach appears to have achieved much more popularity in other countries, such as this New Zealand double-circuit tower.

Height extensions

EE PL1 D2 STD
EE PL1 D2 E5
EE PL1 D2 E10
EE PL1 D2 E20
EE PL1 D2 E40

Examples

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SS PL1 S2; photo courtesy Ian McAulay (CC-BY-NC)
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SS PL1 S10; photo courtesy Ian McAulay (CC-BY-NC)
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SS PL1 S30; photo courtesy Ian McAulay (CC-BY-NC)
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SS PL1 S60; photo courtesy Ian McAulay (CC-BY-NC)
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SWE PL1 D2
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SWE PL1 D10; photo courtesy Jaggery (CC-BY-SA 2.0)

Tower details

Crossarm width is the total width across the widest crossarm. For entries marked † the base width is across the top of the stubs, which is marginally less than the true ground-level width.

Type Source Height Base width Crossarm width
SS PL1 S2 General arrangement diagram 66′–9″ (20.3 m) 15′–0″ (4.6 m)
EE PL1 S2 Tower Bible Chart ED 51155 missing
CE PL1 S2 Tower Bible Chart ED 51156 missing
SS PL1 S10 Erection diagram 69′–1″ (21.1 m) 14′–8¾″ (4.5 m)† 28′–8″ (8.7 m)
EE PL1 S30 Tower Bible Chart ED 51161 missing
EE PL1 S60 Tower Bible Chart ED 51164 missing
CE PL1 S60 Tower Bible Chart ED 51165 missing
EE PL1 ST Tower Bible Chart ED 51168 missing
EE PL1 D2 Tower Bible 79′–3″ (24.2 m) 19′–2716″ (5.9 m)† 33′–31016″ (10.2 m)
EE PL1 D30 Tower Bible 72′–0″ (21.9 m) 22′–0″ (6.7 m) 32′–4″ (9.9 m)
EE PL1 D60 Tower Bible Chart ED 51128 missing
EE PL1 DT Tower Bible 72′–10½″ (22.2 m) 22′–6″ (6.9 m) 45′–0″ (13.7 m)
EE PL1 DT90 Tower Bible 72′–10½″ (22.2 m) 22′–6″ (6.9 m) 45′–0″ (13.7 m)

Examples

The following examples represent opinion only. No tower types were obtained from any official material and thus all designations are speculative.

Sindlesham

132 kV line PBR runs from Reading Main Substation to a junction with a line from Basingstoke that terminates south-east of Hook in the direction of Fleet Substation. All the original towers are presumed to be SWE PL1, although they are not an exact match for the SWE PL1 drawings.

The photographs are from pylon hunt 14 on 12th August 2023; this was my one chance to travel down to Reading on the train and the weather was not co-operative, so the photos are far from ideal.

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SWE PL1 D2
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SWE PL1 D2 detail
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SWE PL1 D2 detail (tower FBR68)
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SWE PL1 D2 detail
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SWE PL1 D10 tower FBR69
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FBR69 detail
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FBR69, 2 × PL16 D2S and L7(c) D60; the line crosses over the M4 between the two PL16 D2S towers

Documentation

See also