Carbon-Pros Analyst BlogEnergy Smart: Dynamic Line Ratings
DLR is best understood in comparison with static line ratings in which the capacity of a transmission line is determined based on worst-case assumptions of full sun, high air temperature, and no wind. Those factors reduce the capacity of a line because hotter lines are more likely to overheat when carry electricity at their rated capacity. If operators knew that clouds were blocking the sun, the weather was cool, and the wind was blowing, they could use the full capacity of the transmission line. It turns out that line tension is a robust predictor of the environmental factors affecting its capacity. The Valley Group produces the tension and environmental sensors along with the software to generate realtime capacity information for grid operators. The system uses data on average line temperature, sag, clearance, and a realtime rating-factor. The system interfaces with the operator's EMS/SCADA and is customized for the operator’s requirements.
Dynamic line ratings improve system reliability, as they allow operators to make fewer corrections in system dispatch, while providing advance warnings of impending thermal/capacity problems. They save money by fully utilizing transmission assets. Aivaliotis says that operators can transmit up to 30% more power over 90% of the time. This extra capacity can be used to manage delays in line construction and management of the network during major system disruptions. DLRs are an enabling technology for more effective use of renewable energy. For example, wind farm production is often limited by transmission constraints. Production is highest when the wind is blowing. That same wind increases the capacity of the transmission system. DLR is the key to unlocking its full capacity.
http://www.nexans.us/US/2008/CaseStudy_NERC_Report_1.pdf
http://www.nexans.us/US/2009/CEA%2025FEB2009.pdf