THEORETICAL-MODEL FOR TEMPERATURE-GRADIENTS WITHIN BARE OVERHEAD CONDUCTORS

A thermal model is described which can be used to calculate the temperature distribution within an energized, stranded overhead conductor. It has been shown that for typical conductor constructions energized to current levels which produce conductor temperatures less than 100°C and for reasonable weather conditions, the maximum temperature difference that exists in stranded conductors is less than 10°C. If conditions reach such a state that birdcaging in the conductor occurs, then temperature differences within the conductor greater than 10°C can result. However, birdcaging will only occur in conductors for which the supporting strands have a coefficient of thermal expansion is greater than that of the conducting strands (ACSR, for example) and only at elevated temperatures, usually well above 100°C. Finally, the results show that ampacity models based on the assumption of an isothermal conductor will provide accurate predictions of a conductor temperature that are between the center and surface temperatures. A few general conclusions are drawn about the influence of temperature gradients on conductor sags.