Analysis of the growth conditions of icicles during insulator icing
Introduction
Icing seriously threatens the safe operation of transmission lines in various ways. Icing can increase the mechanical load on wires and towers, resulting in accidents of wire break, wire galloping, pole and tower collapsing [1], [2], [3], [4]. Insulator icing mainly reduces the insulation properties of insulators, causing partial discharge or flashover accidents [5], [6]. The flashover of ice-covered insulators has always been the focus of researchers at home and abroad, including the ice flashover characteristics [7, 8], the factors affecting ice flashover voltage [9], and the ice flashover models [10], [11], [12].
In 1970, M. Kawai [7] conducted AC flashover tests on ice-covered insulator strings. It is found that the icing on insulator strings always appears unevenly. When the ice thickness increases to a certain value, the flashover can occur under the working voltage. In the study of references [8, 13], the AC ice flashover tests were conducted on composite insulators, and the results show that the AC ice flashover voltage of composite insulators decreases with the increase of ice thickness. When the icing on an insulator string reaches a certain value, the downtrend of ice flashover voltage slows down and gets saturation. Similarly, the study in reference [14] found that the DC flashover voltage of insulators decreases with the icing thickness. Moreover, the ice flashover voltage is also affected by factors such as the surface contamination of insulators, the structure of the insulator shed, and the voltage polarity. The research results of Chongqing University [15] show that the icing weight W of an insulator string and its minimum flashover voltage Uf (W) satisfy a power function relationship Uf (W) = Uf (0) × e-mW, where Uf (0) is the minimum flashover voltage when there is no ice on the insulator string. In addition to the effects of ice weight and thickness, the icing type will also affect the discharge characteristics of ice-covered insulators. The research of N. Sugawara [16] in 1993 shows that different icing types can lead to different flashover voltages, and the withstand voltage of insulator strings covered with icicles is significantly lower than that without icicles. M. Farzaneh [17] and Shu Lichun [18] pointed out that during the process of insulator icing, the presence of icicles will seriously distort the distribution of external electric field of insulators. As a result, the electric field strength at the tip of icicles will increase, making it easier to form partial discharges and ice flashover arcs. As shown in Fig. 1, the researchers equivalently calculate the residual resistance of the ice layer with a semi-cylindrical structure, thus establishing an ice flashover model of insulators. However, the equivalent method is only applicable to the case where the icicles severely bridge the insulator sheds, and is no longer available to other icing types. Otherwise, as present in reference [19], [20], some methods like nanotechnology science can be used for increasing self-capacitance of silicon rubber (SiR) insulators thereby voltage and electric field distribution become more uniform along the string. And how the ice and icicle would affect the electric distribution of insulator strings with improvements need further research.
Therefore, different icing types have significant differences in the damage degree to the insulator's insulation performance. Particularly, the presence of icicles plays a key role. Previous studies have mainly focused on the flashover characteristics of ice-covered insulators and the establishment of ice flashover models. There is a lack of targeted research on the growth mechanism of different icing types on insulators [21], [22].
Makkonen [23] summarized the icing process on conductors into three aspects, namely the collision process of supercooled water droplets on the conductor surface, the capturing process of collision water droplets, and the freezing process of the captured water droplets. To calculate the icing rate, Makkonen [24], Fu Ping [25, 26], and Jiang Xingliang [27], etc. used three efficiencies, namely collision efficiency β1, capturing efficiency β2 and freezing efficiency β3, to characterize the icing efficiency. The insulator icing also satisfies these three processes. But with a much complicated structure, the icing on insulators is significantly different. Based on the difference in density, the insulator icing can be divided into five categories: glaze, hard rime, soft rime, hoarfrost, and snow. The division is conducive to identifying the essential characteristics of icing, but is not good for numerical simulation.
Another division is based on the formation mechanism of ice, and the icing is divided into dry growth and wet growth. For dry-growth icing, the time for liquid water droplets to freeze into solid ice is extremely short, and there is no water film formed on the insulator surface. For wet-growth icing, the water droplets captured on the insulator surface will not freeze completely, and the freezing rate is relatively slow with an unfrozen water film forming on the ice layer. The division of dry and wet growth icing is closely related to the thermal equilibrium process of freezing, which provides an entry point for the numeral calculation of icing and is helpful for the analysis of icing mechanism and the establishment of icing models.
Considering the serious threat of icicles to the operation of insulators, this article creatively redefines the insulator icing into three types according to the characteristics of water film and icicle growth. By analyzing the relationship between the droplet collisions, ice freezing, icicle growth and the flowing of water film, a numerical model is established to simulate the critical condition for icicles growth. The work in this paper can be used in the precise prediction of insulator wet-growth icing with icicles. The research also reveals the formation mechanism of wet-growth icing with icicles, which lays the foundation for the establishment of a three-dimensional numerical model of different insulator icing types.
Section snippets
Accretion characteristics of three icing types
According to the difference in the growth process, insulator icing can be divided into three categories, namely dry-growth icing, wet-growth icing without icicles and wet-growth icing with icicles. When the environment temperature is low and the wind velocity is large, as shown in Fig. 2(a), the icing is dry growth. The supercooled water droplets in the air can completely freeze into ice after colliding with the insulator surface, where the ice particles is white opaque. Compared with
Local droplet freezing efficiency on insulators
Collision of water droplets is the main water source of icing on insulators, but the capturing efficiency of water droplets is different at different locations. Through the simulation of the external airflow field and the tracking of water droplets [28], as shown in Fig. 4(a), the distribution of the collision droplets and local collision efficiency β1 on insulators can be obtained, which will be used for the calculation of captured water mass M0 per unit time. For wet-growth icing, all the
Model of water film flow
The calculation in Eq. (4) is limited to the generation of water film during the insulator icing, and does not consider the flowing of water film. In order to obtain the flowing characteristics of the water film and the critical conditions for icicle growth, this section will analyze the forces of the water film and establish a mathematical model of water film flow.
Flow characteristics of water film on insulator surface
The distributions of the water film on the insulator surface at different temperatures are drawn in TECPLOT as three-dimensional diagrams shown in Fig. 8. The blue area represents that the water film partially freezes into ice (Freezing efficiency β3 < 1), the white area indicates that the water film completely freezes into ice (Freezing efficiency β3 = 1), and the arrows in the figure indicate the flow direction of the water film in various positions.
Under the initial conditions, when the
Conclusion
- (1)
Insulator ice is redefined into three types: Dry growth icing, wet growth icing with icicles and without icicles. The difference between dry and wet-growth is whether the insulator is covered with water films, while the icicle growth is supported by the water supply of water film overflowing.
- (2)
Considering the freezing and flowing balance of the water film on the insulator surface, a model for water film flowing is established based on theories of fluid mechanics and thermodynamics, which can be
CRediT authorship contribution statement
Xingbo Han: Conceptualization, Methodology, Data curation, Writing – original draft, Validation. Xingliang Jian: . Shaojiang Dong: Writing – review & editing. Renxiang Chen: Software.
Declaration of Competing Interest
For this paper titled ‘Analysis of the growth conditions of icicles during insulator icing’, we declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted. Meanwhile, we certify that this manuscript, or any part of it, has not been published and will not be submitted elsewhere for publication while being considered by Electric Power Systems Research.
Acknowledgments
This work was supported financially by Scientific and Technological Research Program of Chongqing Municipal (Grant No. KJQN202000727) and National Natural Science Foundation of China (Grant No.51637002).
Reference (29)
- et al.
Rime icing on bundled conductors
Cold Reg. Sci. Technol.
(2019) - et al.
A novel water droplet size parameter for calculation of icing on power lines
Cold Reg. Sci.Technol.
(2018) - et al.
A 2D numerical study on the effect of conductor shape on icing collision efficiency
Cold Reg. Sci. Technol.
(2017) A simple model for freezing rain ice loads
Atmos. Res.
(1998)- et al.
Comparison on AC icing flashover performance of porcelain, glass, and composite insulators
Cold Reg. Sci.Technol.
(2014) A model of hoarfrost formation on a cable
Cold Reg. Sci. Technol.
(2013)- et al.
A CFD approach for modeling the rime-ice accretion process on a horizontal-axis wind turbine
J. Wind Eng. Ind. Aerodyn.
(2010) - et al.
Two-dimensional modelling of the ice accretion process on transmission line wires and conductors
Cold Reg. Sci. Technol.
(2006) - et al.
Effect of shed configuration on DC flashover performance of ice-covered 110 kV composite insulators
IEEE Trans. Dielectr. Electr. Insul.
(2013) AC flashover tests at project UHV on iced-coated insulators
IEEE Trans. Power Appar. Syst.
(1970)
Flashover performance of pre-contaminated and ice-covered composite insulators to be used in 1000 KV UHV AC transmission lines
IEEE Trans. Dielectr. Electr. Insul.
Study of DC flashover performance of ice-covered insulators at high altitude
IEEE Trans. Dielectr. Electr. Insul.
Application of dynamic model to flashover of ice-covered insulators
IEEE Trans. Dielectr. Electr. Insul.
Dynamic modeling of AC multiple ARCS of EHV post station insulators covered with ice
IEEE Trans. Dielectr. Electr. Insul.
Cited by (7)
Growth characteristics and influence analysis of insulator strings in natural icing
2024, Electric Power Systems ResearchEffect of droplet deformation on discharge at icicle tip of ice-covered insulators during melting period
2022, Electric Power Systems ResearchCitation Excerpt :The electric strength of insulators will decline sharply under the condition of ice cover, and flashover accidents will occur in serious cases, which seriously threaten the safe operation of power lines. Therefore, the study on flashover of ice-covered insulators has been the focus of many researchers [9,10,12,21]. Ice flashover of insulators usually occurs during the melting period when there is water film on the ice surface after icing [4].
Three-dimensional numerical simulation of rime ice accumulation on silicone rubber insulator and its experimental verification in the natural environment
2022, Electric Power Systems ResearchCitation Excerpt :Because the relationship between the inertia of the droplet and its diameter shows a quadratic function, while the droplet inertia has a linear relationship with the v. According to the physical process of insulator icing, the amount of rime ice on the surface of the insulator is determined by mass transfer process [25], as shown in Fig. 8. The research object in this paper is rime icing grown in a dry regime.
Failure probability analysis of transmission towers under ice-wind interaction
2024, Zhendong yu Chongji/Journal of Vibration and ShockEffect of fabrication method on the physical properties of carbon-nanotube/silicone-rubber nanocomposite in high-voltage insulators
2023, Journal of Composite Materials