WHEN TO STRESS OVER CONDUCTOR STRAINS

摘要

Conductor vendors have made the following comments about the variations in Stress-Strain Curves: In the process of analyzing these charts, we found a need to make some changes to the ... charts and the conductors linked to them. We recognize that much of the data supporting ... charts is past retirement age. Accordingly, we are in the process of testing new-production conductor to provide full-range charts and better accuracy... ... warned that wire should only be expected to behave somewhat like the published data and not to expect exactness! Good Advice! The good news is that overload and strength factors combined with conservative loading conditions often result in designs which can accommodate increased tensions. Also, design clearances often include buffers and in most cases, the maximum operating temperatures are rarely encountered. The bad news is that these potential inaccuracies are sometimes not considered when setting requirements and expectations. A big concern is that a mis-placed sense of confidence with technology and software combined with pressure for increased line ratings are pushing the clearance limits. The best thing we as engineers can do is strive to understand the inaccuracies applicable to your project and acknowledge them; educate those who think sag and tension are an exact science; consider providing short term creep graphs for sagging conductor; and be cautious of reducing or eliminating clearance buffers. In fact, we should consider increasing buffers for unique applications. In the vast majority of our project work, we are within limits and bounds where these potential inaccuracies are negligible, but we need to be cognizant of them when working with excessively short or long spans,increased tensions or reduced margins.