Application of fiber-optics to FERC Order 881 on ambient-adjusted ratings (AAR) and dynamic line ratings (DLR)

Transmission capacity shortfalls are a major bottleneck towards many efforts in electrification and renewable energy deployment. One relatively rapid and cost-effective solution to increase transmission capacity is to operate transmission lines as close to their thermal limits as possible, either via ambient-adjusted ratings (AAR) or dynamic line ratings (DLR). However, current AAR and DLR technologies must overcome several challenges to be adopted widespread. Motivated by the desire to reduce the financial and operational hurdles towards implementing AAR and DLR, a novel technique for thermally rating transmission lines using fiber-optic sensors was developed. This technique, known as FORM (FiberOptics for Rating and Measurement), meets the calculation requirements of the US rulemaking on AAR in FERC Order 881 and can also be used for DLR. FORM uses distributed temperature sensing (DTS) with the optical ground wire (OPGW) of the transmission network to spatially and temporally resolve a temperature measurement that reflects both the ambient temperature and solar heating. This measurement alone suffices for a reasonably accurate AAR or DLR implementation but specially designed fiber-optic anemometers (FOAs) can be installed on transmission towers and connected to the OPGW to improve the accuracy of FORM. The conductor temperature was calculated using FORM and was then compared with the same calculation using standard DLR models (CIGRÉ TB 601/IEEE Std. 738) on a 380-kV line over a 12 -month period.