With the recent issue of FERC Order 881, EDM International, Inc. has announced its continued commitment to assist utilities with determining seasonal ratings for their overhead transmission lines.
EDM, together with its strategic partners, jointly developed a transmission line rating methodology that merges meteorological data analyses with thermal ampacity calculations. For the past 25 years, this team has implemented this methodology to help many utilities develop more accurate seasonal ratings that can be used with greater confidence.
Traditionally, conductor ratings are derived from “assumed” values of wind speed, wind direction, temperature and radiation that would lead to a conservative and safe design. However, these values can result in design requirements that are either too lax or too stringent.
In contrast, EDM’s rating methodology uses decades of historical meteorological data to create probabilistic models of wind, temperature, solar radiation and resulting ratings. These models yield sets of weather criteria and ratings with corresponding risk of exceeding maximum conductor temperature. Benefits of this approach include:
- More accurate prediction of weather conditions and their combined effect on ratings
- Determine best fit of months to seasons by comparing ratings or ambient temperature
- Account for disruptions to wind flow caused by trees and structures
- A consistent ratings methodology and ratings are applied across entire service areas
- Full compliance with FERC Order 881, NERC Standard FAC-009-1, IEEE Standard 738, and CIGRE TB 299
