Which of the following is NOT a type of insulator commonly used on transmission lines?

Wooden insulators are not commonly used on transmission lines, which makes this response the accurate choice. The use of insulators in electrical systems is crucial, as they prevent the undesired flow of current and protect the infrastructure.

Porcelain line post insulators, polymer suspension insulators, and porcelain suspension insulators are all widely accepted materials for insulating high-voltage transmission lines. Porcelain has been traditionally favored for its durability and excellent electrical insulation properties. Similarly, polymer insulators have been developed as lightweight, corrosion-resistant alternatives that effectively handle environmental stresses.

In contrast, wooden insulators have largely fallen out of favor in modern electrical engineering due to their susceptibility to weathering, decay, and variable dielectric properties. As a result, they do not meet the reliability standards required for contemporary transmission systems. These characteristics reinforce why wooden insulators are not considered suitable or common for use in high-voltage applications.