132 kV is England’s highest distribution voltage; 275 kV and upwards are transmission voltages, although it appears that Scotland still considers 132 kV to be a transmission voltage. The National Grid was originally constructed as 132 kV, onto which the 275 and later 400 kV Supergrid circuits were overlaid. Most 132 kV lines are now divested out of National Grid and are the responsibility of the regional distribution operators. 132 kV is also the highest voltage to be carried by wood pole lines.
132 kV lines can be carried on a number of structure types:
- “Trident” wood poles
- Heavy duty wood poles
- Metal poles
- Pylons (lattice towers)
Wood pole 132 kV circuits do not use an earthwire, while those on metal poles and pylons do have an earthwire.
Trident poles are notable for their three upward-facing post insulators. The centre post insulator is vertical, while the two side ones lean outwards on intermediate poles. (Section and angle towers have all vertical insulator posts.)
The Trident design covers both single poles and so-called “H-poles”, although the latter type is more akin to a capital letter pi “Π” than “H”.
Trident poles are conventionally made from wood. British Power International’s Protean page shows a Protean metal Trident pole.
The different Trident pole types are illustrated on page 11 (PDF page 13) of Reinforcement to the North Shropshire Electricity Distribution Network document 5.2: Flood Risk Assessment.
Details on 132 kV poles are not clear. Flickr photo 43-97 Pole Top depicts a “43-97” pole, which refers to ENA TS 43-97. It is possible that multiple manufacturers have produced poles to this design, which would account for the variations in design. The same photographer also depicted a 43-97 Angle Pole which is similar in design to those seen in Clapham in Bedfordshire but nonetheless different, with a stouter pole and a different crossarm attachment method.
There are many lattice tower (“pylon”) types designed to carry 132 kV. Some 132 kV lines are even carried on Supergrid towers. See the pylons section for more details.