33 kV power lines (UK)

Contents

• Overview
• Three-tier H-pole double circuit with earthwire
• Two-tier H-pole double circuit
  • Intermediate
  • Section
  • Fuses
  • Terminal
• Single circuit
• See also

Overview

33 kV is the next step up from the more commonplace 11 kV feeds to villages and farms. 33 kV lines are normally found on wooden poles, but steel lattice towers (“pylons”) were historically also used. Where 11 kV feeds are almost always single circuit, 33 kV lines are more typically double-circuit. This can be double-circuit lattice towers, twin single-circuit wood pole lines, or double-circuit wood pole lines. The double-circuit wood pole lines in the UK are quite distinctive in design, although the giveaway for 33 kV is the larger insulators needed for the higher voltage.

Three-tier H-pole double circuit with earthwire

33 kV lines on wood poles generally do not use an earthwire. However, there is an H-pole design used in Essex where the two poles are joined at the top by a tapered metal frame bearing an earthwire (or a pair of straight metal bars in the case of section poles). It has been said that these “used to be quite common in Essex, but many have been phased out”, although no details were given as to what replaced them, nor was it possible to obtain more details. The only line of this type to be reported runs between Ongar substation (east of Ongar) and a field between Coopersale Street and Epping; where it crosses over the M11, two-tier H-poles are used, with an extra insulator in the middle for the earthwire. The three-tier poles are said to carry the nameplate “Cobra”, of which no illustration was provided.

These poles are also unbraced and prone to leaning, just like the two-tier H poles.

Two-tier H-pole double circuit

Double-circuit H-pole design with two tiers: one phase per side on the top tier, and two phases per side on the top tier. Possibly less common than the three-tier design with one phase per tier per side.

Intermediate

Intermediate H-poles are not braced and are often found leaning to one side.

Section

Section H-poles are braced. The poles are spaced further apart than intermediate H-poles. As a consequence, the inner bottom conductors have to pass around the outside of the poles. The extra insulators result in a more “busy” look compared to the three-tier design.

Fuses

Fuses and air break switch disconnectors are ubiquitous on 11 kV. On 33 kV these poles seem to be far less common. The photos below show two single-circuit fuse H-poles on a double-circuit line in Hemel Hempstead. Photos from the old camera. Unfortunately it was not possible to get a clear photo from the fuse/disconnector side.

Terminal

Termination is done on single poles. There is more than one design of terminal pole and it’s not unusual to see different types side-by-side. The Borehamwood and Harpenden photos are from the old camera, hence the rather unsatisfactory quality of some of the images.

Single circuit

Standard 33 kV single circuit wood pole, cylindrical ceramic insulators:

33 kV single circuit can also use twin poles:

See also

• 33 kV lattice tower, Llansanffraid Glan Conwy, Conwy, Wales (Geograph)
• Three-crossarm intermediate H-pole (Wikipedia)
• Three-crossarm section H-pole (Wikipedia)