Electric Power Systems Research 81 (2011) 2147–2154 Contents lists available at ScienceDirect Electric Power Systems Research jou rn al h om epage: www.elsevier.com/locate/epsr Modelling precipitation cooling of overhead conductors Pawel Pytlak a , Petr Musilek a,∗ , Edward Lozowski b , Janos Toth c a Department of Electrical and Computer Engineering, University of Alberta, Edmonton AB, Canada b Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton AB, Canada c Research and Development, BC Hydro, Vancouver, BC, Canada a r t i c l e i n f o Article history: Received 1 April 2011 Received in revised form 9 June 2011 Accepted 9 June 2011 Available online 30 July 2011 Keywords: Transmission lines Conductors Power Meteorology Weather reliability a b s t r a c t This paper presents a precipitation-based conductor cooling model for use in power line ampacity rating applications and line temperature calculations. It is aimed at better modelling of a conductor’s temper- ature by incorporating the line cooling caused by precipitation falling onto power lines. The expanded thermal model quantifies the additional gain of current-carrying capacity for power transmission net- works incorporating advanced Dynamic Thermal Circuit Rating systems. The precipitation cooling model is verified against observations made by a power transmission utility using a commercial line current and temperature sensor clamped onto an actual power transmission line. The accuracy of the precipitation model is assessed both quantitatively using standard error measures, and qualitatively in terms of fit of the model to real world data. The precipitation-based cooling extension shows a significant improvement over IEEE Std. 738-2006 in the modelled accuracy of the conductor temperature. It suggests a substantial increase in available ampacity during periods of precipitation. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The electrical power industry is under increasing pressure to cope with an enlarging market demand for power [1,2]; however, generation capacity upgrades, often in the form of new wind farms, are increasingly hampered by the lack of transmission capacity to bring the additional power to customers [3]. In an ideal situation, power transmission networks would be regularly upgraded to meet the demands. However, this is not always possible because of the major financial costs to upgrade and deploy new transmission lines, and increased government and environmental regulations such as laws aimed at preserving the natural habitat. Consequently, trans- mission companies are seeking alternatives to expand the capacity available with the existing infrastructure. One modern approach is to use Dynamic Thermal Circuit Rating (DTCR) systems to identify and make use of existing underutilized power lines [4]. DTCR systems [5] are capable of increasing the capacity of existing power transmission lines by dynamically rating them in real time using actual operating conditions, rather than by using conservative estimates based on near-worst-case operating sce- narios [6]. On average, DTCR systems are capable of doubling the capacity of a power line at a given point [7]. DTCR systems pro- vide the power transmission industry with a more cost-effective approach to expand available transmission capacity [8]. DTCR sys- ∗ Corresponding author. E-mail address: Petr.Musilek@ualberta.ca (P. Musilek). tems decrease the time for new power generation sources to deliver energy to markets, since DTCR installations to deployed relatively quickly and do not require new infrastructure construction. In order to improve the accuracy of weather-based DTCR sys- tems [9], this paper proposes an extension to the generally adopted power line thermal model described in IEEE Std. 738-2006 [10]. The increase in accuracy is achieved by the inclusion of conduc- tor cooling caused by falling precipitation. To assess the real-world performance of the new model, it is used to predict the conduc- tor temperature of an actual power line in operation. The modelled temperatures are compared with measurements from a sensor on a live transmission line. This paper also presents an assessment of the potential gains in transmission capacity that can be achieved by using the precipitation cooling thermal model. These potential gains in ampacity are assessed using real meteorological conditions recorded during actual precipitation events, rather than estima- tions based on average or typical meteorological/climatological conditions during periods of rain or snow. 2. Background The power that can be sent through a transmission line is largely limited by the conductor’s maximum operating temperature. This maximum temperature limit is selected to ensure that safety reg- ulations are met, line clearances are satisfied, and to minimize the loss of tensile strength due to annealing when the conductor is operated at high temperatures [11]. In order to ensure that all rel- evant line constraints are satisfied, the maximum current rating, 0378-7796/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.epsr.2011.06.004