Calculation model and experimental verification of equivalent ice thickness on overhead lines with tangent tower considering ice and wind loads
Introduction
In 2008, an extreme ice storm occurred in South China, severely damaging power networks in 14 provinces; snowy and freezing weather in South and East China led to a continuous ice and snow storm in 2018, resulting in large-scale mechanical failures and electrical decrease accidents, such as collapse of towers and poles, breaking of conductor strands, damage of hardware fittings, flashover of insulators and burning of conductors. Transportation and production, as well as the safety and property of people were seriously [Farzaneh and Chisholm, 2009; Ji et al., 2016; Li et al., 2009]. Therefore, accurate icing prediction on transmission lines is crucial for the icing prevention in power grid. It is essential for power departments to implement rapid and efficient anti-icing/de-icing measures to prevent major ice accidents [Jiang et al., 2018; Rui et al., 2017; Cui et al., 2021].
Recently, extensive research has been performed on the icing prediction models of transmission line. Scholars have established empirical icing models by combining icing events and meteorological parameters, such as the Lenhard empirical model, Kuoiwa model, and Imai model [Lenhard, 1955; Kuroiwa, 1965; Imai., 1953]; theoretical models based on the various parameters of icing, including the Goodwin model [Goodwin et al., 1983]; and numerical models considering the physical icing process, such as the Makkonen heat balance model [Makkonen, 1998, Makkonen, 1990] and Makkonen numerical model [Makkonen, 1998, Makkonen, 2000]. To reveal the formation of conductor icing and factors that lead to disasters, icing monitoring mainly include on-site observations at ice observation stations, meteorological model monitoring, video image monitoring, and mechanical model monitoring [Hu et al., 2017; Yin et al., 2016; He et al., 2017].
In addition, wind loads can considerably influence mechanical models in practice, which should be modified in the case of wind load. Based on the variation of mechanical characteristics on conductor, the icing prediction models of transmission lines have been developed. The impact of wind load on the deviation angle of insulator strings, as well as the ice load on conductor mechanical characteristics were considered. Keyhan, H. et al. analysed the wind-conductor dynamic interactions after icing in the stress analysis of overhead transmission line towers [Keyhan et al., 2012, Keyhan et al., 2013]. However, the circular or elliptical ice section on conductors adopted in this study could not completely represent the icing characteristics of ice and snow disasters in power grid [Zhang et al., 2011]. The meteorological department provides relatively accurate forecasts of ice and snow weather over a large area; however, nevertheless, the microtopography and microclimate icing are the main reasons for ice disasters, which remains challenging to power grid [Jiang et al., 2018]. The icing prediction models of conductors based on meteorological parameters is not effective enough due to the inaccurate measurements without considering the ice and wind loads. Therefore, the results obtained by the proposed model are questionable. It is essential to build a model to accurately calculate the icing thickness on overhead lines.
In this paper, a model for predicting equivalent ice thickness is developed, considering the impact of ice and wind loads. The aerodynamic characteristics of icing conductors are investigated. Moreover, the results are verified on the basis of the field data obtained from the State Field Scientific Observation and Research Station of Xuefeng Mountain Energy Equipment Security of Chongqing University. The findings of this study provide a theoretical reference for anti-icing and mitigation in power grid, and have crucial engineering value to ensure the safety of power system by avoiding ice and snow disasters.
Section snippets
Simulation model of the aerodynamic characteristics for iced conductors
The shape of an iced conductor is irregular and uniform. The wind acts on the conductor to produce not only the drag force in the downwind direction, but also the lift force in the crosswind direction. Numerous experimental results have shown that, drag force and lift force per unit length (FD, FL) generated by the wind load on the iced conductor are as follows:where ρ is the air density (kg/m3), V is the wind speed (m/s), l represents the characteristic length of the
Calculation model and test verification of equivalent ice thickness for tangent tower transmission lines
It is assumed that: (a) the length of overhead conductor and diagonal span are equal; (b) a certain value is considered the angle between the wind direction and conductor in the same span, the comprehensive ratio load of ice and wind is evenly distributed along the diagonal span, and the size and direction are the same everywhere [Bozhi, 2008]. Therefore, the wind condition of overhead line can be obtained by calculating the mechanical parameters of oblique parabolic conductor with uniformly
Conclusions
(1) The aerodynamic parameter models of the crescent and sector-shaped iced conductors are established. The drag coefficients of two iced cross-section conductors decrease with the increase in the wind speed. However, the wind speed shows no apparent effect on the lift coefficient. When 0° < attack angle (α) < 45° or 135° < α < 180°, the drag coefficient of crescent iced conductors decreases with the increase in the ice thickness. For 45° < α < 135°, the drag coefficient increases with the rise
Declaration of Competing Interest
None.
Acknowledgements
This work was supported by National Natural Science Foundation of China (NSFC Project No: 52107142, 51637002), Joint Fund of National Natural Science Foundation of China (No: U1834204). The authors gratefully acknowledge the contributions of all members of the external insulation research team at Chongqing University for their work.
Bingbing Dong was born in Anhui province, China, in 1987. He received the Ph.D. degree in engineering from Chongqing University, China in 2014. He is currently an Assistant Professor with the School of Electrical Engineering and Automation, Hefei University of Technology, Hefei, China. His main research interests include high-voltage external insulation, and transmission-line icing and protection. Dr. Dong has published over 30 papers about his professional work.
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Bingbing Dong was born in Anhui province, China, in 1987. He received the Ph.D. degree in engineering from Chongqing University, China in 2014. He is currently an Assistant Professor with the School of Electrical Engineering and Automation, Hefei University of Technology, Hefei, China. His main research interests include high-voltage external insulation, and transmission-line icing and protection. Dr. Dong has published over 30 papers about his professional work.
Xingliang Jiang was born in Hunan Province, China, on July 31, 1961. He received the M.Sc.and Ph.D. degrees in electrical engineering from Chongqing University, Chongqing, China, in 1988 and 1997, respectively. His employment experience includes Wuhan High Voltage Research Institute, Wuhan, Hubei Province; and the College of Electrical Engineering, Chongqing University. His research interests include high-voltage external insulation and transmission-line icing and protection.
He is Chinese Society for Electrical Engineering, CSEE Fellow and the member of working groups of CIGRE B2.29 and IWAIS. Dr. Jiang has published two books and over 300 papers about his professional work. He received the First-Class Rewards for Science and Technology Advancement from China in 2013; the Second-Class Rewards for Science and Technology Advancement from China in 2005 and 2009; IEEE Caixin Sun and Stan Gryzbowski Lifetime Achievement Award in 2020; Beijing Government in 1998; Ministry of Education in 1991 and 2001, respectively; the first-class Reward for Science and Technology Advancement from the Ministry of Power in 2004 and 2005; the Second-Class Reward for Science and Technology Advancement from the Ministry of Technology in 2005; the First-Class Reward for Science and Technology Advancement from the Ministry of Education in 2006; and the First-Class Reward for Science and Technology Advancement from Chongqing City in 2006, 2008 and 2018, Hunan Province in 2011.
Ze Xiang was born in Sichuan, China, in 1987. He received the Ph.D. degree in engineering from Chongqing University, China in 2014. He is currently a senior engineer with State Grid Chengdu Power Supply Company, Chengdu, China. His main research interests is external insulation and transmission line’s icing. Dr. Xiang has published over 20 papers about his professional work.