Probabilistic forecasting of dynamic line rating for over-head transmission lines

Rating of an overhead transmission line is defined as the maximum current that the line can safely carry without damaging the conductor. This current limit has been treated conventionally as a constant under the worst weather conditions. Dynamic line rating (DLR) is the current limit determined by real weather conditions surrounding the conductor. Using DLR has potential to increase the line rating and reduce the congestion. Transmission lines are normally designed in line sections consisting of multiple spans. The DLR problem is thus difficult considering the spatial nature of capacities along a transmission line as well as the requirement of description of uncertainties. In this paper, a novel probabilistic DLR forecasting method is developed. Capacities at selected spans are first forecast as random variables with means and standard deviations to capture the spatial nature and uncertainties. The line rating for the entire line is then forecasted as a random variable determined as the minimum of span capacities. Expected values and important percentiles of forecast ratings are derived. Numerical testing for a 230 kV transmission line demonstrates the increased line rating with high confidence by using our method.