Blaw Knox K8790
Contents
Overview
Two 66 kV (or 66/33 kV) power lines were constructed between Preston and Peel (outside Blackpool) using towers designed by Blaw Knox. Application for planning consent was issued in 1946–1947. Electricity North West have identified one of the line tower types as 33/66 kV Blaw Knox K8790 D3, designed in 1945. The existence of two line tower types, a strange tension–suspension types and various alternative angle and terminal towers makes it impossible to be sure what Blaw Knox K8790 covered unless Electricity North West are willing to elaborate further on the tower details.
Most of the angle towers bear a strong resemblance to PL16 (with which it is contemporary) making it a “baby PL16” type (the line towers don’t resemble those of PL16).
The same towers appear on several other lines, including one in Kent (SEE region). Whether the Kent line or Preston lines came first remains to be determined.
General data
| Designed for | Preston Corporation |
|---|---|
| Design contractor | Blaw Knox, Milliken Brothers branch |
| Height (straight line tower) | ? |
| Voltage | 66 kV |
| Dates back to | 1945 (drawings) |
| Known conductors | Single |
| Design conductor | ? |
| Circuit count | Double |
| Earthwire arrangement | Single, double |
Lines
Discovered lines to date, all 33 kV:
- RPA: Preston to Blackpool, using what may be the original D3 tower design
- RPB: Preston to Blackpool, starting at Ribble GSP substation on an L7 DT (tower RPB 2A) and undergrounded at Staining Wood Farm solar plant outside Blackpool, with tap-off points including Clifton and Wrea Green (part of the route is on parallel wood poles); same tower suite as RPA except for the D3
- CT and CM, two short lines (12 and 5 towers respectively) in Middleton, originating near Whitegate substation in Middleton Junction, Greater Manchester; same line tower as RPB
- TA and TB, two short lines between Fleetwood and Thornton-Cleveleys; these in part use tension towers with suspension insulators
- Medway Grid–Halling–Luddesdown, from Medway Grid substation to a cable sealing end near Luddesdown (over a mile past Halling); same tower suite (RPB D3) except for a custom DT
A lone RPB D3 tower used to exist on Darenth Wood Road in Dartford, Kent, but it has since been demolished.
Tower forms
The diagrams below are all scaled to 8′–6″ crossarm spacing, as per Blaw Knox K9906, the 1945 Blaw Knox type shown in [Nicholls] and the SEE SL8 terminal gantry. This seems to fit in with the assumed 10′ height extensions and gives earthwire peak heights in (mostly) exactly whole number of feet (one came out as 6′–6″).
The D3 towers are sufficiently narrow as to rely solely on X bracing without wider bracing panels, making guessing the standard heights of the towers tricky; the heights of these towers are an assumption based on the most frequent heights encountered.
Various types may not be K8790. The alternative D30 and D60 and the RPB2A and TA7 terminal towers appear to be a separate suite similar to NWE SL4 but seemingly smaller. Situations have occurred where towers from another suite have been brought in and reclassified. For now, none of these types are being definitively designated K8790, as the only tower type apparently K8790 is the RPB D3. Why the alternative D30 seems to be inherently taller remains a mystery. It is only used in two zero-deviation positions on RPA although in one of these it is erected at an angle to the line.
The RPA85 and RPB75R DT (or DT45) tower has provision for a double earthwire crossarm and indeed the lines originally commenced on DDT towers at Penwortham. RPB1 appears to have had around a 45° entry angle, meaning that the tower could have been designated either DDT or DDT45.
All tower designations below except the RPB D3 are speculative based on measurement of route deviation as part of an audit of all lines known to use these towers.
All diagrams are scaled to 12 pixels per metre.
No double earthwire towers are now known to exist. Both RPA and RPB began on DDT towers at Penwortham. RPB1 had an entry angle of around 45°. RPB2 then was a DDT60, then RPB3 was a DD3, based on historic photographs. There is not a clear-enough view of RPB2 to be able to draw it, but very approximate attempts at RPB1 (DDT) and RPB3 (DD3) are included above. RPB1 is gone, and RPB2 is replaced with a terminal tower (no. RPB2A) of a different design. RPA85 and RPB75R have the vestigial peak of a DDT tower where the earthwire crossarm is meant to be attached, just as is the case with most PL16 DT towers (the DT was a later derivation from the DDT by omission of the earthwire crossarms).
Examples
Out of range.
Tower details
No data.
See also
- Terminal tower, Ribble Grid Supply Point (Geograph)
- Line tower (Geograph)
- Preston’s Power Stations (Flickr), including: (the photograph used for the basis of DD3 is not from this album and is of unknown origin)