Assessing the dynamic rating of overhead transmission lines

SUMMARYThis paper addresses the achievable advantage of the dynamic rating of overhead power lines based onthe continuous monitoring of the ambient temperature and wind speed. Starting from their measured profileson a typical summer day, the corresponding possible current loading of the line could be determined overthe24hours.Itisthencomparedwiththeconventionallineratingcalculatedusingthemaximumdailytemperatureand the typically assumed value of 0.6m/s for the wind speed. The additional daily transmitted energyresulting from the dynamic line rating (DLR) could be found. The procedure is applied to lines of differentconductor radii. Results indicate an achievable increase in the daily transmitted energy of about 40%.Copyright # 2007 John Wiley & Sons, Ltd.key words: power transmission lines; conductors; heating; limiting; temperature; wind; monitoring 1. INTRODUCTIONAs a result of deregulating the power industry, the utilities are continuously exploring the availablepossibilities to run their activities in the most economical way. This includes, among other measures,the proper selection and/or design of new equipment, improving the utilization of already existingresources such as the application of line compensation, the forced cooling of equipment, and FACTSdevices,aswellasthecosteffectiveoperationoftheirsystemswithoutcompromisingeitherthesupplyreliability or its quality. This is valid for all activities pertinent to the generation, transmission,distribution, and the supply eventually committed for export to other utilities. Focusing on thetransmissionfacilities,Reference[1]givesdetailedguidelines fortheproperratingoftheundergroundand overhead transmission lines, and transmission system substations taking into account thecompliance with the corresponding standards. Useful tables are given addressing the line conductorampacity criteria, such as the relevant weather conditions (e.g., the ambient air temperature, windspeed, and solar insolation), maximum continuous conductor operating temperatures, and theconductor properties.