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Wind tunnel tests were carried out to obtain the static aerodynamic characteristics of crescent iced 4-bundled conductors with different ice thicknesses, initial ice accretion angles, bundle spaces, and wind attack angles. The test models were made of the actual conductors and have a real rough surface. Test results show that the influence of wake interference on the drag coefficients of leeward subconductors is obvious. The interference angle range is larger than 20° and the drag coefficient curves of leeward subconductors have a sudden decrease phenomenon at some certain wind attack angles. The absolute value of the lift and moment coefficient increases with the increase of the ice thickness. In addition, the galloping of the iced subconductor may occur at the angle of wind attack near ±20° and the wake increases the moment coefficient. The variation of initial ice accretion angle has a significant influence on the aerodynamic coefficients. The aerodynamic coefficient curves exhibit a “moving” phenomenon at different initial ice accretion angles. The bundle spaces have a great influence on the moment coefficient of leeward thin ice-coated conductors. With the increase of ice thickness, the bundle spaces generally have little influence on the aerodynamic coefficients.

China is a mountainous country. The mountain area accounts for more than 60% of the land area. The mountainous southwestern region is rich in hydropower resources and it is also the main power generation area of the West-East Electricity Transmission Project. Most of the transmission lines will cross valleys, rivers, and micrometeorological areas in mountainous southwestern regions, where the conductors are easily ice-coated in winter. Under certain conditions, the ice-coated conductor will produce large amplitude and low frequency self-excited vibration, which is called galloping [

There are lots of researches about the aerodynamic characteristics of ice-coated conductors. As early as 1932, Den Hartog [

It is worth noting that most of the scholars currently use smooth surface conductor models in experiments. In this paper, the sectional models were made of the actual conductors and have a real rough surface. In addition, research on the influence on the bundle space and the initial ice accretion angle of the crescent iced 4-bundled conductors is still rare. Therefore, tests were carried out to obtain the variation laws of static aerodynamic characteristics of crescent iced 4-bundled conductors with different ice thicknesses, initial ice accretion angles, bundle spaces, and wind attack angles in the wind tunnel. The obtained results may provide the fundamental data for the development of antigalloping techniques of ice-coated 4-bundled conductors.

The wind tunnel tests were carried out in 1.4 m × 1.4 m low-speed wind tunnel at the China Aerodynamics Research and Development Center (CARDC). The maximum wind velocity is 60 m/s. The test model in wind tunnel is shown in Figure

Model in the wind tunnel.

Iced 4-bundled conductors

Real conductor

The experimental setup

The actual transmission conductors were chosen for the test model, whose type is LGJ400/35 (

Definition of wind attack angle and aerodynamic force and ice accretion angle.

Definition of wind attack angle and aerodynamic force

Definition of ice accretion angle

The variation of ice thickness

The aerodynamic characteristic parameters of the ice-coated conductor include drag coefficient, lift coefficient, and torsional coefficient. The dimensionless characteristic parameters of the ice-coated conductor are defined as follows:

The variations of subconductors’ aerodynamic coefficients with different ice thicknesses and wind attack angles are shown in Figures

Aerodynamic characteristics of bundled conductors with respect to wind attack angle (space: 485 mm).

Subconductor 1

Subconductor 2

Subconductor 3

Subconductor 4

Aerodynamic characteristics of subconductors with respect to wind attack angle (space: 485 mm).

Subconductor 1

Subconductor 2

Subconductor 3

Subconductor 4

Aerodynamic characteristics of bundle conductors with respect to wind attack angle (space: 485 mm).

Subconductor 1

Subconductor 2

Subconductor 3

Subconductor 4

Den-Hartog coefficient of conductors varying with ice thickness.

Figure

When the ice thickness increases to 20 mm or 30 mm, the sudden decrease phenomenon of drag coefficient on subconductors 2 and 3 weakens at the angle of attack of 0°. This is mainly because the outline of the conductor is closer to the streamlined body when the ice thickness of the conductor is thicker. The effect of wake interference on aerodynamic characteristics of the ice-coated conductor with streamlined body is smaller than that of the conductor with blunt body. When the wind attack angle is −45° or +45°, the streamlined body has been converted to a similar blunt body, which significantly enhances the interference effect on the leeward conductor. The drag coefficient curves of subconductors 2 and 3 also vary significantly. Due to the variation of wind attack angle, the outlines of the windward conductors vary with the direction of inflow. This also indicates that the windward conductor’s outlines play an important role in wake interference on the leeward conductors.

Figure

It can be seen that the lift coefficients of subconductors are substantially antisymmetric at the range of wind attack angle from −45° to +45°. Figure

The absolute value of the lift coefficient increases with the increase of the ice thickness in the range of wind attack angles, especially at the angle of wind attack near ±20°. The absolute value of the lift coefficient increases rapidly with the increase of the ice thickness and forms a sudden peak phenomenon at these two angles. This phenomenon is similar to the wing stall, which is a kind of flow separation phenomenon. When the ice thickness is relatively thin, the outline of the conductor is close to the bluff body, and the flow separation phenomenon is not obvious.

Figure

It can be seen from Figure

The above results show that although the variation laws of aerodynamic coefficients of subconductors with attack angle are basically the same at different ice thicknesses, the measured values are obviously different. In this paper, the Den-Hartog criterion is performed to estimate the possibility of galloping. Aerodynamic damping less than zero is the necessary condition of instability to gallop; the formula for the criterion is as follows:

It can be seen from Figure

The aerodynamic coefficient curves of subconductors 1 and 2 varying with the wind attack angles under different initial ice accretion angles are shown in Figures

Effect of initial ice accretion angle on

Subconductor 1

Subconductor 2

Effect of initial ice accretion angle on

Subconductor 1

Subconductor 2

Effect of initial ice accretion angle on

Subconductor 1

Subconductor 2

It can be seen from Figure

Figures

The aerodynamic coefficient curves of subconductor 2 varying with the wind attack angles under different bundle spaces are shown in Figure

Effect of bundle space on the aerodynamic characteristics of subconductor 2 (thickness: 10 (30) mm, initial ice accretion angle: 0°).

It is observed that the variation of the bundle space generally has little influence on the drag and lift coefficient, even for subconductor 2, which is greatly influenced by the wake interference. When the conductor is with thin ice coating (

Wind tunnel tests were carried out to obtain the static aerodynamic characteristics of the widely used ice-coated 4-bundled conductors (LGJ400/35) in a transmission system with different ice thicknesses, initial ice accretion angles, bundle spaces, and wind attack angles. The main conclusions are as follows:

The windward conductor’s outline is the key factor to affect the aerodynamic characteristics of iced conductors.

The influence of wake interference on the drag coefficient of subconductors is obvious. The interference angle range is larger than 20° and the curves of leeward conductors’ drag coefficient have a sudden decrease phenomenon at some certain wind attack angles. This sudden decrease phenomenon gradually decreases with the increase of ice thickness.

The absolute values of the moment coefficients of leeward conductors are always larger than those of the windward conductors, which means the wake increases the moment coefficient.

When the conductor is with heavy ice coating, the curve of the lift and moment coefficient will form a sudden peak phenomenon at the angle of wind attack near ±20°, and the galloping of the iced subconductor may occur near these two angles of wind attack.

The variation of initial ice accretion angle has a significant influence on the aerodynamic coefficients. The aerodynamic coefficient curves exhibit a “moving” phenomenon for the same nominal wind attack angle at different initial ice accretion angles. For the leeward subconductors, the “moving” of aerodynamic coefficient curves is not uneven due to the influence of wake interference.

The bundle spaces generally have a great influence on the moment coefficient of subconductor 2 for the conductors with thin ice coating. With the increase of ice thickness, the bundle spaces generally have little influence on the aerodynamic coefficients.

The authors declare that there are no conflicts of interest regarding the publication of this paper.

This work was supported by the National Natural Science Foundation of China (Grant no. 51478069) and Chongqing Natural Science Foundation (Grant no. CSTC2017JCYJB0210).