SS-PL1
Contents
Overview
Following on from their original tower design for the CS PL1 and SEE PL2 contracts, Milliken Brothers produced a new tower suite that went on to be used for most of the remaining PL1 contracts. [Standard Tower Types] uses the description “SS-PL1” for this type, although it appears that SS PL1 was not the first contract 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). The Mid-East England (MEE) and South East England (SEE) PL1 contracts used towers from Callender’s and GEC/Pirelli-General.
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 looks as though it were 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.
General data
| Designed for | CEB |
|---|---|
| Design contractor |
Milliken Brothers Callender’s (SWE PL1 S2) |
| Found |
|
| 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 |
Contracts
Revised Milliken towers were used for the following PL1 contracts:
- CE PL1 (Milliken T161)
- NWE PL1 (Milliken E112)
- NEE PL1 (Milliken E136)
- SWE PL1 (Milliken E141)
- EE PL1 (Milliken E142)
- SS PL1 (Milliken E164)
NWE PL2 contained the special towers associated with NWE PL1, such as river crossing towers.
Revised Milliken towers can also be found south of the Thames. Seven such towers can be found on UKPN route PSB (Chessington–Leatherhead), starting with the DT in Leatherhead (PSB1). The Leatherhead DT is visually identical to EE PL1 DT; the other Milliken towers are D2 (three of), D30 (two of) and D60. UKPN refer to the Milliken type used on this line as “PL6” without a CEB region prefix.
Two more revised Milliken towers can be found nearby on UKPN route PGC (West Weybridge–Chertsey): one D2 and one D60. These two towers are are listed as “PL1”, again without a CEB region prefix. This is otherwise an SEE PL1a line, re-rated to 33 kV.
Custom S2 towers
At least two CEB regions used custom line towers on the single-circuit lines. In the SWE region, single circuit line towers were of a Callender’s design. In the CE region, at least one line used a Milliken design that was a forerunner to CE PL3 S2.
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.
The SWE PL1 S2 drawings are annotated “SWE PL1(a)&(b)” which appeared to suggest that the Callender’s S2 towers were used only on additional contracts. Examination (via Street View) of single-circuit lines in the SWE area shows only the Callender’s S2, and this is backed up by a remark in [Condensed] that single-circuit SWE PL1 is Blaw Knox (i.e. Milliken) except the S2 which is a Callender’s type. The meaning of PL1(a)&(b) remains unknown, but the S2 GA drawing does not have these suffixes in the details panel; they are added to a separate annotation.
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).
Lines
SWE
Confirmed so far:
- Exeter to Bridgwater, now truncated to Taunton to Bridgwater
- Exeter to Kingsteignton
- Newton Abbot to a junction south of Ipplepen
- Fraddon substation to Hayle substation
- The double circuit SWE PL1 line from Lydney splits south of Arlingham into two single-circuit lines, one continuing to Castle Meads substation in Gloucester and the other circling around to Cambridge Arms switching station on the opposite side of the River Severn.
The only two known SWE PL1(a)&(b) drawings are for the S2, drawn in 1931. These are annotated “T(4) BEA - L45 - East Yelland - Fraddon”. Such a line would have to date from at least 1948, by which time the construction of a PL1-type single-circuit line seems unlikely. Two lines currently exist between these locations: a double-circuit PL16 line, and an L6 line (4VW).
Other uses of the SWE PL1 S2 tower:
- Substitute tower on a 33 kV line, Buxton, Derbyshire
- Substitute tower on a CS PL1 line, Bishopton, Renfrewshire
Tower forms
Broadly, the tower designs should be essentially identical across all the revised Milliken contracts. Some differences do exist, in particular with the terminal towers. The diagrams below are not exhaustive with regards to contracts.
The following diagrams are shown to scale at 12 pixels per metre.
Single circuit towers
In the SWE area at least, long straight line spans used S10 towers with no deviation.
The S90 type can be seen outside Dumfries (SS PL1) and Andersea, Bridgwater (SWE PL1). The design is similar to the 6-foot-peak Glenlee ST; with short crossarms, pilot insulator sets are needed for the outer angle conductor(s) to maintain correct clearances for the jumpers. No official designation is known.
Double circuit towers
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.
[Clearances] indicates that the crossarm dimensions for NWE PL1 D90 are identical to those of SWE PL1 D90.
Terminal towers:
The extra width of the EE PL1 DT crossarms suggests that this tower was designed for 45° entry angle; this pattern matches SEE PL1a where the DT and DT45 towers share the same wide crossarms of a plan very similar to that of EE PL1 DT.
Western Region chart DL8238 (“Superstructure Dimensions of Double circuit 132KV Towers (S.W.E. P.L.1 Design)” notes that “DT60°A similar to D.T60° but with auxiliary crossarms, and all crossarms square.” The corresponding single-circuit chart DL8237 notes “ST60°A tower similar to ST60° but with auxiliary crossarms.” [Condensed]. 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.
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. A symmetrical (all pointed crossarms) example can be found at the Burton-on-Trent substation; the next tower appears to be a D60 with a 6-foot peak.
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
Examples
Tower details
The table below is not complete; figures are only given for tower types where data is presently available.
See dimensions on the site guide page for a key to the tables.
| Type | Source | Height | Base width | Crossarm width | |
|---|---|---|---|---|---|
| EE PL1 D2 | D2 | ED51102 | 79′–3″ (24.2 m) | 19′–6″ (5.9 m) | 31′–3⅝″ (9.5 m) |
| NEE PL1 D2 | LT2830-6B | ||||
| SWE PL1 D2 | DL8238 | 31′–0″ (9.4 m) | |||
| NWE PL1 D2 | LT530-11C | ||||
| SWE PL1 D10 | D10 | DL8238 | 82′–1″ (25 m) | 20′–0″ (6.1 m) † | 33′–0″ (10.1 m) |
| EE PL1 D30 | D30 | ED51119 | 72′–0″ (21.9 m) | 22′–0″ (6.7 m) | 32′–4″ (9.9 m) |
| NWE PL1 D30 | LT530-13A | ||||
| SWE PL1 D30 | DL8238 | ditto approx. † | |||
| EE PL1 D60 | D60 | ED51128 | 72′–6″ (22.1 m) | 22′–0″ (6.7 m) | 34′–4″ (10.5 m) |
| SWE PL1 D60 | DL8238 | ditto approx. † | |||
| SWE PL1 D90 (4 foot peak) | D90 | BK35/28016 | 72′–10½″ (22.2 m) | 22′–0″ (6.7 m) † | 27′–9″ (8.5 m) |
| SWE PL1 D90 (6 foot peak) | DL8238 | 74′–10½″ (22.8 m) | |||
| NWE PL1 DX | DX | E112-160A | 74′–0″ (22.6 m) | 22′–0″ (6.7 m) | 39′–6″ (12 m) |
| SWE PL1 DX | DL8238 | ditto approx. † | |||
| EE PL1 DT | DT | ED51143 | 72′–10½″ (22.2 m) | 22′–0″ (6.7 m) | 45′–0″ (13.7 m) |
| EE PL1 DT90 | |||||
| SWE PL1 DT | DL8238 | 72′–6″ (22.1 m) | 22′–0″ (6.7 m) † | 32′–8″ (10 m) | |
| SWE PL1 DT60 | 74′–6″ (22.7 m) | 50′–0″ (15.2 m) | |||
| SWE PL1 DT60A | |||||
| EE PL1 S2 | S2 | ED51155 | 67′–3″ (20.5 m) | 15′–0″ (4.6 m) | 23′–4⅛″ (7.1 m) |
| SS PL1 S2 | BK35/31900 | ditto approx. * | |||
| CE PL1 S2 | T161-19 | 23′–0½″ (7 m) | |||
| SWE PL1 S2 (Callender’s) | DL8237 | 64′–6″ (19.7 m) | 14′–0″ (4.3 m) | 22′–5″ (6.8 m) | |
| SS PL1 S10 | S10 | BK35/31942 | 69′–1″ (21.1 m) | 15′–0″ (4.6 m) | 25′–5″ (7.7 m) |
| SWE PL1 S10 | ED51161 | ditto approx. † | |||
| EE PL1 S30 | S30 | ED51161 | 60′–6″ (18.4 m) | 19′–0″ (5.8 m) | 23′–11″ (7.3 m) |
| SWE PL1 S30 | DL8237 | ditto approx. † | ditto approx. † | ||
| EE PL1 S60 | S60 | ED51164 | 60′–6″ (18.4 m) | 20′–0″ (6.1 m) | 27′–8″ (8.4 m) |
| SWE PL1 S60 | DL8237 | ditto approx. † | |||
| CE PL1 S60 | ED51165 | ||||
| SWE PL1 S90 | S90 | DL8237 | 60′–6″ (18.4 m) ‡ | 20′–0″ (6.1 m) † | 23′–8″ (7.2 m) |
| EE PL1 ST | ST | ED51168 | 60′–6″ (18.4 m) | 20′–0″ (6.1 m) | 24′–0″ (7.3 m) |
| SWE PL1 ST | DL8237 | 60′–6″ (18.4 m) ‡ | 20′–0″ (6.1 m) † | 24′–0″ (7.3 m) | |
| SWE PL1 ST60 | |||||
| SWE PL1 ST60A | |||||
The ED drawings are from [Enhanced tower bible]. DL8237 and DL8238 are from [Condensed].
† assumed base width at ground level based on back-to-back over top of stubs
‡ DL8237 gives 60 foot total height for S30, S60, S90 and ST/ST60/ST60A, which is being taken here to denote height to top of concrete, with total height to ground level being 60′–6″
* assumed, but source material is illegible
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.
See also
- NWE PL1 D30, Carlisle (Flickr)
- Same tower, different view (Flickr)
- SS PL1 single circuit line (Flickr album)
- SWE PL1 D10 tower in Whitewater Country Park, Hook; this example lacks the large brackets for the insulators (Flickr)
- SWE PL1 transposition tower, Broadclyst Station, Exeter (Flickr)
- Sequential SWE PL1 D10 towers, Tregof Village, Swansea (Flickr)
- Same towers as above, in silhouette (Flickr)
- Construction of brand new PL1(c) towers on a 33 kV line (Flickr)
- SS PL1 DT-type junction, Kendoon (Alamy)
- SS PL1 DT-type junction, Kendoon (Alamy)
- CE PL3 S2 and Stafford–Wolverhampton S2 (Flickr)