Case study of the increase in capacity of transmission lines in the Chilean system through probabilistic calculation model based on dynamic thermal rating

Abstract

The usual practice in operators is to specify conductor thermal limits based on worst-case weather condition scenarios. However, given that environmental conditions change constantly, so does the ampacity of the conductor. This is why line thermal limitation should not be established in a conservative, fixed or invariable way. In the case of Chile, the Independent System Operator (ISO) establishes current-carrying capacity curves. Nevertheless, these are only a function of the ambient temperature in the presence of the sun. Such methodology is insufficient since it does not consider the effect of wind as the main conductor cooling mechanism.The main contribution of this paper is the development of a new approach for a probabilistic current calculation model based on dynamic thermal rating. This approach accounts for the spatial and temporal variation of weather conditions along a line. The approach maximizes the line’s current capacity by employing an iterative process based on the span identification that limits the conductor ampacity. Furthermore, the approach includes temperature restrictions to avoid conductor mechanical problems.The model is applied in the Chilean system, particularly to the Maitencillo–Nogales 220 kV transmission path. The new current limitations established by the proposed approach are compared to those set by the Chilean ISO and show significant increases in the current-carrying capacity of the lines and hence a better use of NCRE generation to lower production costs and CO2 emissions.