SEE PL1a

Contents

• Overview
  • General data
• Lines
• Tower forms
  • Single circuit
  • Double circuit
  • Examples
  • Tower views
    • D2
    • D30
• Tower details
• Examples
  • Bedford
  • Luton South Substation
  • Garston
• See also

Overview

South East England (SEE) PL1a appears to be one of the original grid schemes, covering approximately the South East England region north of the Thames. The towers appear to have been designed by GEC although the Tower Bible gives the designer as Pirelli. This is in contrast to most PL1 schemes which used Milliken towers. The southern half of the South East England region was designated PL1(b) which used Callender’s towers.

The same towers were used for the initial lines within the Mid-East England region (both single and double circuit) and are thus tentatively MEE PL1 (no drawings have been recovered that would confirm this). The erection diagram for the S2 tower is annotated SWE PL2; possibly only the single circuit towers were used in SWE PL2. Such towers are yet to be located.

SEE PL1a should not be confused with SWE PL1(a)/PL1(b) which was a Callender’s type.

SEE PL1a and PL1(b) share a common design feature of an integrated anti-climbing device. Most tower suites use adjustable anti-climbing devices; these can be positioned within a range of heights from the ground. PL1a and PL1(b) instead set the anti-climbing device at specific height from ground level: 19 foot for SEE PL1(b) D2, 25 foot for D30 and 18 foot 5 inches for PL1a D2. The heights all differ and correspond to the bracing structure, and are not where the network operators want the anti-climbing devices positioned. In practice, conventional adjustable anti-climbing devices are used instead at a lower position, leaving vestigial projections at the originally-intended height. These projections can be used as a recognition aid to narrow down a tower to PL1a or PL1(b); this helps with single circuit towers as those are less distinct from eah other than double circuit towers. The diagrams on this site omit anti-climbing devices, but the integrated ones in PL1a and PL1(b) are shown as they are a part of the tower.

General data

Contractor	GEC?
Found	()
Height (straight line tower)	78′–9″ (24.0 m) (D2) 66′–9″ (20.3 m) (S2)
Voltage	132 kV
Dates back to	1929 (known drawings), 1931–32 (approvals)
Known heights	STD E5 (+5′) (D2) E10 (+10′) E20 (+20′) (not listed for DT/DT45) +20 (+20′) (only listed for D30/DT/DT45) E30 (+30′) (D2, D30, D60) E40 (+40′) (D2, D30, D90) +40 (+40′) (only listed for D30) E60 (+60′) (D30, D60)
Known conductors	Single
Circuit count	Single, double
Design conductor	Presumed to be 0.175□″ SCA (now 175 mm² Lynx ACSR)

Lines

Various lines have been found to date. A few are confirmed and detailed below:

Double-circuit lines confirmed so far:

• Elstree–Sundon, believed to part of SEE PL1a; this has been repeatedly sliced and diced, with the Luton end now L4(m). Redbourn uses L7(c) and there are also PL16 and even one PL4/WGR towers in the line. The line from the Luton end now terminates at Redbourn, while from the south it diverts at Redbourn to Piccotts End in Hemel Hempstead.
• The CS PL1 line from Abernethy to Dundee has a diversion between Errol (56.400° N 3.230° W) and Grange (56.422° N 3.178° W) built using SEE PL1a towers.

Single-circuit lines confirmed so far:

• Peterborough–Lincoln; this line started close to the edge of the SEE–MEE border at Peterborough and continued to Lincoln. The south end of the line is now double circuit as far as the B1443 between Ashton and Maxey, south-west of Market Deeping. Sleaford Renewable Energy Power Station outside of Sleaford connects to the line at an unidentifiable tower that is most likely a PL1(c) ST45 or ST90.
• Ipswich–Colchester survives as Bramford–Lawford; the single-circuit portion of the line now only runs from the east of Ipswich down to Lawford substation, east of Little Bromley (between Manningtree and Colchester).
• York–Ferrybridge: this line starts at Osbaldwick Grid Substation (initially underground) before terminating near Monk Fryston, continuing underground from there to Ferrybridge A Substation.

Tower forms

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

Single circuit

The front face of the single-circuit towers has one left crossarm and two right crossarms but the drawings above are reversed to be consistent with those of other series to reduce visual confusion.

Double circuit

PL1a transposition towers are omitted from the Tower Bible. It appears that the transposition tower type is derived from the D30 just as with PL1. The preliminary transposition tower drawing above is based on examples such as the one near Hemel Hempstead in Hertfordshire. The transposition rigging is a suggestion based on photographs of the corresponding arrangements in other tower suites.

Examples

Tower views

D2

D30

Tower details

Crossarm width is the total width across the widest crossarm.

Examples

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

Bedford

There is a SEE PL1a tower on the line believed to be SEE PL2 (Bedford to Little Barford); this tower was a later addition to the line, possibly used to terminate part of the line during remodelling. It currently functions as an S60 tower, with a deviation angle of 48°. The outline matches both ST45 and ST90 and, with no auxiliary crossarms, ST45 is the presently chosen designation. The tower number is PAA 2.

Luton South Substation

Part of the Elstree–Sundon 132 kV network, this branch between Sundon Substation and Elstree Substation provides power to Luton from the south by way of the Luton South Substation (51.874° N 0.400° W). Largely an L4(m) route, the final two towers are PL1a. The pictures were taken on 11th September 2021.

Garston

Garston is on the Elstree–Sundon 132 kV line, although this network is disconnected from Sundon at Redbourn, with its only exit being the spur to the substation at Piccotts End in Hemel Hempstead right before the disconnection point. Both PL1a and PL16 towers can be found in Garston. The line passes through Bushey Mill Substation via a PL16 DT, with downleads allowing power to be tapped off for Watford and Bushey. See the PL16 page for further parts of this line.

See also

• SEE PL1a DT90, Watford 132 kV substation (Flickr)
• PL4 DDT90 and SEE PL1a DT90, Watford 132 kV substation (Flickr)
• PL16 DDT90 and SEE PL1a DT90 with extended top crossarms, Gowhole, New Mills (Flickr)