Strength and security overhead

The recent blackouts, first in North America and then in Europe, can lead to questions such as Why did that happen? and Aren't electricity transmission lines made to sustain major loads and resist extreme climatic conditions? Although it may be impossible to predict all disaster scenarios, a number of measures can be taken to ensure maximum security. IEC 60826, covering design criteria of overhead transmission lines, addresses some of these important questions.

Produced by IEC Technical Committee 11 (Overhead lines), the new standard provides both structural and mechanical design criteria (i.e. loadings and strengths requirements) for overhead transmission lines 45kV and greater, based on reliability concepts and allowing to design lines for varying levels of reliability using probabilistic or semi-probabilistic methods. The publication is divided into two parts, the first being normative and the second informative.

This standard also provides minimum safety requirements to protect people from injury, as well as to ensure an acceptable level of service continuity (safe and economical design). Although the design criteria in this standard apply to new lines, many concepts can be used to address the reliability requirements for refurbishment and updating of existing lines.

Coherence and co-ordination
First and foremost, this standard allows for the designing of lines as a coherent system and for the coordinating of the strengths of components within the system to achieve the desired reliability. According to Elias Ghannoun, convenor of the TC 11 working group that developed IEC 60826: "It is expected that this approach should lead to an overall economical design without undesirable mismatch between the various components constituting the overhead line."

Ghannoun adds that "users can derive many benefits from designing their lines in accordance with this standard. Electrical utilities, transmission lines engineers, overhead line contractors and manufacturers of line components, who currently design lines according to deterministic principles, will be able to design more cost effective lines and/or increase the reliability of their lines for the same total cost. All users will also benefit by designing their lines for the climatic conditions prevailing in their service areas."

In conclusion, Ghannoun says that "this third edition of IEC 60826 shows several improvements: it was completely reviewed and simplified and converted into an International Standard (the previous edition was a Technical Report)."

IEC 60826 Ed. 3.0 (2003-10)
Design criteria of overhead transmission lines
ICS codes: 29.240.20 - TC 11 - 243 pages