Learn to recognize T&D pylons, foundations, insulators, cables, bushings and arresters

T&D pylons and equipment

Recognizing the type of transmission & distribution pylons and their equipment is kind of hard if you don’t know where to look for. There are many variations that look similar and you must have sharp eyes to see the details. This technical article tends to sharpen your eyes.

Description of the equipment (line with pylon, cables and substation with transformers, switch yard…) is in the following paragraphs.

Contents:

1. 1. The structures and pylons
      1. Type of pylon by function
      2. Type of pylon by material used
   2. Conductor arrangements
   3. The foundations
   4. Insulators, bushings and arresters
      1. Insulators, bushings and arresters types
   5. Conductors
      1. Conductor types
   6. Substations

1. The structures and pylons

Structures for T&D overhead lines take a variety of shapes depending on the type of line. Structures may be as simple as wood poles directly set in the earth, carrying one or more cross-arm beams to support conductors, or “armless” construction with conductors supported on insulators attached to the side of the pole.

Tubular steel poles are typically used in urban areas. High-voltage lines are often carried on lattice-type steel towers or pylons. For remote areas, aluminium towers may be placed by helicopters.

Concrete poles have also been used. Poles made of reinforced plastics are also available, but their high cost restricts application.

A large transmission line project may have several types of towers, with “tangent” (“suspension” or “line” towers) towers.

These are intended for most positions and more heavily constructed towers used for turning the line through an angle, dead-ending (terminating) a line, or for important river or road crossings.

Depending on the design criteria for a particular line, semi-flexible type structures may rely on the weight of the conductors to be balanced on both sides of each tower.

More rigid structures may be intended to remain standing even if one or more conductors is broken. Such structures may be installed at intervals in power lines to limit the scale of cascading tower failures.

1.1 Type of pylon by function

Anchor pylon

Anchor pylons or strainer pylons are employed at branch points as branch pylons and must occur at a maximum interval of 5 km, due to technical limitations on conductor length.

Branch pylon

Branch pylon is a pylon that is used to start a line branch. The branch pylon is responsible for holding up both the main-line and the start of the branch line, and must be structured so as to resist forces from both lines.

Tension tower

A tension tower with phase transposition of a traction current line for single phase AC 110 kV, 16.67 Hz.

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1.2 Type of pylon by material used

Wood pylons

For support pylons a straight trunk impregnated with tar is usually used, which carries one or more cross beams with the conductor cables on the top.

In Germany wood pylons are used as a rule only for lines with voltages up to approximately 30 kV, while in the U.S. wood pylons are used for lines with voltages up to 345 kV.

Concrete pylon

Concrete pylon or concrete pole, is an electricity pylon made from reinforced concrete. Concrete pylons are manufactured at the factory and put up at the power line’s right of way. Concrete pylons, which are not prefabricated, are also used for constructions taller than 60 meters.

Such pylons look like industrial chimneys and some of these structures are also used as chimneys. In China some tall pylons of power line crossings of wide rivers were built of concrete.