Weather-dependent versus static thermal line ratings [power overhead lines]

Some of the practical limitations on the use of weather-dependent thermal rating methods for overhead transmission lines are explored. A distinction is made between weather-dependent thermal ratings for a single span and for an entire line. Based on hourly historical weather data for Rochester, NY, USA, it is demonstrated that while the probability distribution of the weather-dependent thermal rating of each span in a line is similar, the probability distribution of line ratings is dependent upon the orientation of the spans in the line. The maximum weather-dependent line ratings are found when all spans are parallel. Minimum weather-dependent line ratings are found for lines whose span orientations vary. Historical weather data are studied in order to estimate minimum predicted thermal ratings for 1 and 4 hours into the future. It is found that such minimum predicted thermal ratings are not greatly in excess of traditional static thermal line ratings