Porcelain and Composite Longrod Insulatoes - A Solution for Future Line Requirements

Insulators of the longrod-design have been in use in Central Europe for more than 40 years; in several countries they have replaced the previous cap and pintype insulators (in the USA often referred to as suspension-type insulators). More recently, the advantages of longrod insulators have found new places of installation also in other countries, specifically in high-voltage transmission lines being confronted with heavy solid-layer pollution problems. Theoretical considerations anticipate also considera advantages with an HVDC-insulation. Of special interest is also the longrod design as composite longrod insulator. In spite of their worldwide application and the excellent service experiences gained - especially in the case of conventional longrod insulators - the technical characteristics of these insulators are not yet adequately known in many places. Thus, this paper presents a survey on the electrical and mechanical properties as well as the insulation performance under pollution, performance under power arcs, and the interference-voltage behavior. Furthermore, the particulars and differences during installation and operation of these insulators in comparison to strings of cap and pin-type insulators are pointed out. The technologically sensible dimensioning limitations are described. The observations prove that longrod insulators represent an advantageous solution and are best suited for future line requirements.