TABLE OF CONTENTS This chapter describes the basic input data required and terminology used for the design of substation steel structures, overhead line towers and poles.
The industry is currently revising its approach to the general concepts of tower design. The loadings and related strengths required for overhead line design have normally been determined by Statutory Instruments, the client s or the consulting engineer s specifications. The international standards applicable are IEC 60826, Design criteria for overhead lines , EN 50341 Overhead lines exceeding 45 kV and EN 50423 Overhead electrical lines exceeding AC 1 kV up to and including AC 45 kV . IEC 60826 gives clear and straightforward guidance using many of the graphs and tables directly from BS8100 and in its National Normative Aspects (NNAs) EN 50341-3-9 points to loading derived from the same standard for use in the UK. The same criteria are not necessarily applicable in all territories, where, for example, averaging time for wind speeds may be an issue. See also report IEC/TS 61774 (Overhead lines meteorological data for assessing climatic loads).
The newer ENs offer the alternatives of a probabilistic approach to design or an empirical approach based upon national/local experience. Such issues are the responsibility of the specialist structural engineer. Therefore this chapter gives very basic examples to allow the electrical engineer to understand the fundamental principles and terminology involved rather than the specific methodologies.
It should also be noted that open-terminal substation equipment support structures are nowadays being fabricated more and more from aluminium alloy...
