Transmission Line Insulators and Support Structures: Types and Forces

Insulator Types and Classification

B. Suspension Insulator String

Consists of several insulators, the number of which depends on the line voltage and required isolation level. Used for alignment, it supports the conductor by setting the suspension clamps.

C. Strain (Tie) Insulators

Used at angle supports, and at the beginning and end of the line, where mechanical stress is high. The conductor is secured using tension clamps.

D. Classification by Constitution

• Simple: One-piece construction.
• Compound: Consists of two or more pieces.

E. Classification by Installation Site

Insulators are classified for indoor or outdoor use, including those designed for high humidity or rain environments.

F. Classification by Fit and Finish

Insulators are classified as having metal frames or being without metal frames.

9. Transmission Line Supports

Regulations stipulate that supports must be made of concrete, metal, or other suitable material possessing high mechanical strength and resistance to atmospheric agents.

Given the critical role supports play in the line, they are classified as follows:

Alignment Supports

Used in straight sections of the line. They primarily carry the conductors and are subjected mainly to vertical forces (compression).

Angle Supports (Tension Towers)

Placed at the apex where the line changes direction (angle). They are subjected to the resultant force from the line tension and must withstand significant bending stress.

Dead-End Supports (Start/End of Line)

Must withstand the full longitudinal tension force exerted by the conductors along the entire line.

Structural Forces on Supports

Vertical Forces (Efforts)

These are due to the weight of the conductors and potential support overload caused by ice accumulation.

Transversal Forces (Efforts)

These are caused by wind action on the support structure and the lateral pull exerted by the conductors.

Longitudinal Forces (Efforts)

Traction caused by the longitudinal tension of the main conductors, especially critical at dead-end supports (start and end of the line).

Support Material Features

Concrete Supports

Made of concrete reinforced with a metal frame consisting of interconnected longitudinal and transverse iron rods. They typically have a compression strength of 230–430 kg/cm². The iron rods provide mechanical resistance against bending and torsion.

To further improve the mechanical properties of concrete supports, they are manufactured using the following methods:

• Glass fiber reinforcement
• Spinning (Centrifugal casting)
• Prestressed concrete

These constructive methods reduce internal air volume, thereby increasing mechanical strength.

Advantages of Concrete Supports

• High mechanical strength, allowing for longer spans.
• Unlimited lifespan and low maintenance requirements.

Disadvantages of Concrete Supports

They are typically heavy and can be fragile under certain impact loads.