Study on the Discharge Characteristics along the Surface and Charge Movement Characteristics of Insulating Media in an Airflow Environment

Abstract

The gas–solid interface of high-voltage insulating equipment is a weaker part of insulating equipment insulation, and preventing the occurrence of discharge along the surface of insulating equipment is a critical problem for high-voltage insulation. This article investigates the discharge characteristics and charge movement characteristics of insulating media under an airflow environment. The surface discharge characteristics of the insulating medium in the airflow environment were obtained by using a high-velocity airflow test platform, and the surface discharge voltage characteristics, discharge path characteristics, and force conditions of the discharge process were analyzed. The surface charge motion characteristics of the insulating medium in the high-velocity airflow environment were also tested, and the distribution characteristics, dissipation characteristics and conduction mechanism of the surface charge of the insulating medium in the high-velocity airflow environment were revealed. The research results showed that: the discharge voltage along the insulating medium surface gradually increases with the increasing velocity of airflow; the discharge path along the surface of the insulating medium gradually shifts backward under the action of airflow; under the action of airflow, the charge on the insulating medium surface is blown away, thus reducing the charge concentration on the insulating medium surface; the trap level center of the insulating medium gradually decreases under the action of airflow, which provides the conditions for the charge blowing effect on the insulating medium surface. This investigation supplies the theory support for the protection of insulation equipment in an airflow environment and technical guidance for the insulation design of insulating equipment in an airflow environment to ensure the secure and steady running of insulating equipment in high-speed trains and high-voltage transmission lines.

1. Introduction

During the running of a high speed train, high speed airflow is formed around the train, and the electrical equipment located on the roof of the train is in high-velocity airflow conditions for a long time. As high speed trains are running, the insulation equipment on the roof of the train is subject to the airflow caused by the operation of the train, and the airflow speed around the insulation equipment on the roof of the train is as high as 100 m/s [1,2,3,4,5,6]. At the same time, the outer insulation equipment of the power system’s high-voltage electric transmission line is in the airflow environment for a long time, and the insulation equipment of the transmission lines is also subject to airflow, and the insulation performance of the electrical equipment of the transmission lines is affected by the airflow environment. High-voltage transmission lines in windy environments are also subject to airflow speeds of up to 50 m/s [7,8,9,10,11]. During the operation of electrical equipment, the electrical equipment exposed to the airflow environment is subject to the effect of the airflow environment, and the discharging characteristics and charge motion characteristics along the insulating medium surface in the airflow conditions are still unclear. Therefore, it is important to study the discharge characteristics of the insulating medium surface and the characteristics of charge movement of the insulating medium surface in the airflow environment.

A large number of studies have shown that the main factors affecting the discharge along the surface include: gas composition and pressure, geometry of the insulation material, surface treatment of the insulation material, etc. [12,13,14,15].

A team from Tsinghua University investigated the propagation characteristics of the stream injection in various media materials in a homogeneous electrical field and revealed that the required electrical field and the rate of stream injection development for stable development of the stream depend on the properties of the dielectric material [16]. The researchers obtained the DC corona initiation voltage and corona ion current at different air pressures and humidity in artificial climate tanks using needle plate electrodes, and the calculated and experimental results showed that the corona initiation voltage decreases with decreasing air pressure, which is mainly due to the expansion of the ionization region caused by the increase in the effective ionization coefficient and the enhancement of ion collision ionization in the high field strength region [17,18,19]. Comparing the development of the streamer along the insulating surface under a uniform electric field with the development in air only, it was found that the “surface” component of the streamer develops steadily at a faster rate than the steady development in air only [20,21,22,23]. However, the above studies do not take into account the effect of the airflow conditions on the discharging along the surface.

The airflow environment has great impact on electrical discharge behavior. Some researchers have studied the electrical discharge behavior of the air gap in an airflow environment [24,25,26,27,28,29]. A research team from Tianjin University conducted corona tests under different wind speed conditions and discovered that wind introduction may change the ion drift path and thus affect the corona electrical discharge behavior, and the greater the wind speed the greater the effect on the corona discharge [30]. The energy balance of ion development can be changed when the airflow is in the direction of ion drift. The airflow makes the ions move as well by the Coulomb force as well as by the airflow movement. Due to the frequent collisions between neutral molecules from the air stream and charged ions in the direction of the air stream, the discharging process is influenced by the air stream. The above study shows that the discharge in the airflow environment varies greatly compared to when there is no airflow. However, most of the above research is about the effects of airflow conditions on air gap electrical discharges, which rarely concern the electrical discharges along the surface of insulating media in airflow conditions.

In this paper, the discharge characteristics and charge motion characteristics of insulating media under an airflow environment are studied by using high-speed airflow environment insulation media along the surface of the discharge test platform built independently, as well as through a test to obtain the airflow conditions while using the insulation media along the surface of the discharge characteristics, which will show an analysis of the airflow environment insulation media along the insulating media surface of the discharge voltage characteristics, discharge path characteristics, and discharge process force situation.

2. Sample Preparation and Experiment Setup

The experimental sample is a 5 cm × 5 cm × 0.5 cm silicone rubber insulating sheet, and a needle-plate electrical electrode made from copper foil is immediately attached to the silicone rubber insulating sheet for the along-the-surface electrical discharge test of the insulation media under the airflow environment. The needle electrode is an isosceles triangle with a base length of 1 cm and a height of 3 cm. The plate electrode is a rectangle of 5 cm in width and 1 cm in length. The needle electrode’s axis is vertical to the plate electrode, and the distance from the needle electrode to the plate electrode is 1 cm. The detailed parameters are shown in Figure 1.

To avoid the effect of residual charge, the surface of the sample was wiped with anhydrous ethanol and deionized water and placed in a drying oven in a cool place to dry before the test. In order to study the influence of air velocity and airflow direction on the electrical discharge characteristics along the surface of the needle–plate electrode, the experiment was carried out by changing the airflow direction and setting different airflow speeds. The anode is connected to the needle electrode and the cathode is connected to the plate electrode. The relationship between the airflow direction and the position of the needle plate electrode setting is presented in Figure 1.

To investigate the surface discharge characteristics of insulating media in airflow conditions, a set of surface discharge test system for insulating media under airflow conditions was independently established in the laboratory, as shown in Figure 2.

The system for testing the discharge of insulating media along the surface in an airflow environment includes five parts: centrifugal fan, airflow contraction section, test section, airflow expansion section, and airflow measurement section. The centrifugal fan is powered by a 22 kW triple phase synchronous electric motor at 1470 r/min, and the maximum wind speed of the experimental section can reach 135 m/s. The airflow speed is regulated by the speed controller. The anemometer is FC-002/002A with a measuring range from 0 to 80 m/s. The cross-sectional area of the experimental section is 240 × 180 mm², and the air velocity ratio between the experimental section and the airflow outlet is 1.78. The anemometer is designed to be installed at the airflow outlet, and the air velocity of the test section reaches 135 m/s when the anemometer measures air velocity at 76 m/s. The air velocity is adjusted according to the converted air velocity to obtain the corresponding air velocity of the test section.

During the experiment, the temperature of air was 293 K, with 64% humidity and 97 kPa air pressure. At the start of the experiment, the discharge voltage value of the insulating dielectric pin-plate electrode along the surface is obtained and used as a reference value. The air velocity is set to the expected value. The voltage is applied at the electrode ends of the insulating medium pin plate and regulated to 60% of the reference value of the along-the-surface discharge voltage; then, the voltage is gradually increased in steps of 2% of the reference value every 5 s until the discharge along-the-surface of the insulating medium occurs. The airflow velocity of the insulating medium discharge along the surface was set to 0, 20, 40, 60, and 80 m/s, and the airflow direction was between 0 and 90 degrees, as shown in Figure 1. During the experiment, observation equipment was used to observe and photograph the insulation medium’s surface discharge process under airflow conditions and to record the experimental data. In order to reduce the experimental error, the same set of experiments needs to be repeated five times.

3. Characteristics of Discharge along the Surface of the Insulating Media in an Airflow Environment

3.1. Discharge Voltage Characteristics along the Surface of the Insulating Media in an Airflow Environment

The variation law of electric discharge voltage with airflow speed along the surface of the insulating medium under different airflow directions in an airflow environment was tested to obtain the results shown in Figure 3.

We can see from Figure 3 that when the airflow direction is perpendicular to the needle plate electrode axis, that is, when the airflow inlet angle is 0°, the discharge voltage along the insulating medium surface without airflow is 25.9 kV; when the air velocity is 80 m/s, the discharge voltage along the insulating medium surface reaches 36.2 kV, which is 39.7% higher than the discharge voltage along the surface without airflow. When the airflow direction is parallel to the axis of the needle plate electrode, that is, when the airflow inlet angle is 90°, the electrons move from bottom to top, and the airflow suppresses the movement of electrons to the anode, and the discharge voltage along the insulating medium surface increases as the air velocity increases. When no airflow is available, the discharge voltage along the insulating medium surface is 25.9 kV; when the air velocity is 80 m/s, the discharge voltage along the insulating medium surface is 50.3 kV, which is 94.2% higher than the discharge voltage along the insulating medium surface without airflow. At this time, compared with the discharge voltage along the surface when the wind speed is the same but the direction is perpendicular to the axis of the needle plate electrode, the discharge voltage along the insulating medium surface increases by 38.9%, and the discharge voltage along the insulating medium surface in the airflow conditions has obvious differences in different airflow directions.

3.2. Discharge Path Characteristics of Insulating Media Surface in an Airflow Environment

The along-the-surface discharge images of the insulation media at different airflow velocities in the airflow environment were obtained by the test. Figure 4, Figure 5, Figure 6 and Figure 7 show the test images of the discharge along the surface of the electrodes for needle plates of the insulating medium under different conditions. Figure 4 presents the corona electrical discharge images of the needle plate electrode along the surface of the insulating medium when there is no airflow. Figure 5 shows the corona discharge image of the needle plate electrode along the insulating medium surface when the air velocity is 80 m/s. Figure 6 shows the image of the along-the-surface discharge of the needle plate electrode along the insulating medium surface when there is no airflow. Figure 7 shows the image of along-the-surface discharge of the needle plate electrode along the insulating medium surface at the air velocity of 80 m/s.

It can be concluded from the test that the along-the-surface discharge characteristics of the insulating medium in the airflow conditions are different from the discharge characteristics of the insulating media surface when there is no airflow. Figure 4 shows the corona discharge light area in the absence of airflow. When no airflow is available, the corona discharge light area is symmetrically distributed along the vertical direction on both sides of the electrode space. Figure 5 shows that the corona discharge luminescence region is shifted to the right due to the airflow when the airflow velocity is 80 m/s. Figure 6 shows the discharge path along the insulating medium surface when there is no airflow, and the discharge path of the insulating medium is almost perpendicular to the plate electrode. Figure 7 shows the discharge path along the insulating medium surface when the airflow velocity is 80 m/s. In the airflow environment, the discharge path along the face of the insulating medium is deflected along the airflow direction, and the discharge path along the insulating medium surface is significantly bent and deflected.

3.3. Force Analysis of Insulating Medium Discharge along the Surface in an Airflow Environment

In contrast to the along-the-surface discharge where there is no airflow, the characteristics of the along-the-surface discharge in the airflow conditions are influenced by the airflow. Under the action of airflow, the electrons and ions in the airflow will acquire a force parallel to the direction of airflow. The trajectories of electrons and ions will be deflected along the horizontal direction, and some ions and electrons will even be blown away from the insulating medium surface.

In the airflow conditions, the secondary electron emission will become difficult due to the change in the trajectory of the ions in the airflow conditions. Due to the airflow, the electrons emitted by the cathode and the positive ions emitted by the anode will be subjected to a force parallel to the direction of the airflow. As shown in process (1) of Figure 8, due to the ability of any solid surface to adsorb gas molecules, secondary electrons will be generated when primary electrons encounter a thin layer of gas on the surface of the insulating medium. At this time, the negative and positive ions are also affected by the airflow, and the trajectory is deflected, as shown in process (2) in Figure 8.

To further analyze the influence of the electrical field on the discharge along the surface in the airflow environment, the electrical field distribution of the insulating dielectric needle plate electrode on the silicone rubber surface was simulated by finite element software, as shown in Figure 9.

It is found by simulation that the electrical field strength is highest at the central axis of the insulating dielectric needle plate electrode. Figure 10 shows the electric field intensity distribution curves of the insulating dielectric needle plate electrodes at different distances from the center axis. By comparing the electrical field intensity at different distances from the central axis in Figure 10, it can be found that when farther away from the central line, the electric field intensity is smaller.

By comparing the electrical field strengths at different distances from the center line presented in Figure 10, it is clear that the electric field strength decays more with increasing distance of the electrical field line from the center line. Therefore, the electron and ion trajectory in the airflow environment deviates from the central electric field line, since the field strength on the trajectories of electrons and ions is smaller at this time, such that the electrons obtain a smaller electric field force, and therefore obtain less energy from the electric field, resulting in less energy hitting the thin layer of gas on the insulating medium surface, such that the ability to generate electrons by hitting the thin layer of gas is weakened, which finally inhibits the development process of discharge along the surface of the insulating medium.

By simulating the electric field distribution of the needle plate electrodes, it is possible to distinguish the discharge into a strong field region and a weak field region. The ions are subjected to different forces at different locations of the electrical field, which is an important factor causing the change in discharge in the airflow environment. By analysis, the force analysis of ions in different positions is shown in Figure 11.

When the ion is in the strong field region, the ion is subjected to a strong electric field force, the force of the electrical field plays a dominant role in the motion of the ion. When the ion moves into the weak field area, the force of the electrical field on the ion movement of the dominant role is weakened, and the movement of ions is dominated by the traction effect of airflow. When the ion is farther away from the central electrical field, the force of the electrical field is weaker, and compared with the no-airflow environment, the ion is more likely to bias the direction of the airflow. This is also a major factor in the deflection of the discharge path along the face of the insulating medium in the airflow environment.

4. Charge Movement Characteristics of Insulating Media Surface in an Airflow Environment

To obtain the movement features of the insulation media surface charge under airflow conditions, a surface charge test experiment of the insulation media surface charge under airflow conditions was carried out. The test setup is presented in Figure 12.

The surface charge test system in an airflow environment is used to measure the surface potential change feature of the insulation medium in an airflow environment, which is used to deduce the surface charge movement characteristics of an insulating medium in an airflow environment. The test system mainly includes five parts: wind speed system, temperature control system, high voltage DC power supply, electrode system and data acquisition system. The wind speed system consists of a high power fan and wind speed measurement system, and the test airflow speed is adjustable from 0to 60 m/s; the data are collected in a computer through an information acquisition card. The test electrode adopts the needle–grid–plate electrode. The electrodes with needles and grid electrode are pressurized by two independent high-voltage DC power supplies, and the electrodes for the plates are grounded. The needle electrode is made of a stainless steel needle with a 0.5 mm radius of curvature, the grid electrode is made of stainless steel, the copper plate is used as the electrode with needles, and the plate electrode is grounded. The surface potential test chamber is made of an acrylic plate of size 50 cm × 50 cm × 50 cm; in order to eliminate the interference of temperature and humidity on the dissipation results, desiccant temperature and humidity detection equipment are placed in the test chamber.

To avoid influence of residual charge on the test results, the sample surface was wiped with anhydrous ethanol and deionized water before the test and placed in a drying oven for more than 24 h to ensure that the surface was dry, and the surface was confirmed to be free of residual charge by the experiment. The needle electrode distances from the grid electrode and the grid electrode distance from the sample surface are both 5 mm, the probe is at a distance of 3 mm from the surface of the sample, and the voltage signal is collected through the data acquisition module. The ambient temperature is 293 K, relative humidity is 64%, and air pressure is 97 kPa. During the test, the silicone rubber specimen is placed on the copper plate, and a DC voltage of +10 and +2 kV is applied to the electrodes with needles and the gate electrode, respectively, and the specimen is charged for 3 min under the action of airflow. After charging, the charge distribution characteristics of the insulating medium surface under airflow environment are tested. At this time, the gate electrode is removed, and the surface charge distributional characteristics of the insulating medium are measured by the step scan method.

4.1. Charge Distribution Characteristics of Insulating Media Surface in an Airflow Environment

The surface charge distribution features of the insulating medium under airflow conditions were obtained through tests, as shown in Figure 13, Figure 14, Figure 15 and Figure 16, for the insulation dielectric surface charge distributions under four different airflow speeds.

As can be seen from Figure 13, the distribution of charge is mainly concentrated in the middle of the insulating medium when there is no airflow, that is, directly below the needle electrode, and spreads in all directions, with the most charge accumulating in the middle and less charge accumulating outward. With the introduction of airflow, it is found that the distribution of the surface charge on the insulating medium is changed in the airflow conditions, and the accumulation area in the airflow environment will occur as a shift along the airflow direction, and the larger the air velocity, the larger the offset. When the airflow velocity is 10 m/s, the accumulation area is no longer in the middle of the insulation medium, as shown in Figure 14. When the airflow velocity reaches 60 m/s, the main accumulation area of the insulating dielectric surface charge has reached the edge of the insulating medium due to the airflow, as shown in Figure 16. From the test, it can be found that the airflow has a significant effect on the distribution of charge on the insulating medium surface. When there is no airflow, the charge distribution is mainly concentrated in the middle of the insulating medium surface. This means that the insulating medium surface charge accumulates most in the middle position directly below the needle electrode, and decreasingly spreads outward from the needle tip. When there is airflow, the insulating media surface charge accumulation area will move along the direction of the airflow, and the stronger the airflow velocity, the greater the charge deflection distance.

In the airflow conditions, the charge injection process of the needle electrode is not only affected by the electric field force and airflow traction, but also collides with the gas molecules and ions in directional motion, which deflects the charge trajectory and eventually leads to the change in charge position on the insulating medium surface, and the whole process is illustrated in Figure 17 and Figure 18.

This test phenomenon from the charge point of view shows that the airflow has a traction effect on the charge movement characteristics during the discharge process on the insulating medium surface, and the airflow traction plays an essential part in the deflection characteristics of the development process of the discharge along the insulating medium surface.

4.2. Dissipation Characteristics of Surface Charge of Insulating Media in an Airflow Environment

To investigate the effect of airflow conditions on the surface charge dissipation behavior of the insulating medium, experimental studies on positive and negative surface charge dissipation at different airflow velocities were carried out, and the positive and negative surface charge dissipation characteristic curves at different airflow velocities were obtained, as shown in Figure 19 and Figure 20.

To facilitate the analysis, the charge dissipation at different airflow velocities is defined by the dissipation rate in time period t, where the dissipation rate is calculated as shown below.

$$D=\left|\frac{V(0)-V(t)}{V(0)}\right|\times 100\%$$

(1)

where V(0) is the voltage at the initial moment of the end of charging, and V(t) is the voltage at moment t. In this case, t = 600 s was chosen. After statistical analysis, the average dissipation rates of positive and negative polar charges were obtained for different airflow speeds, as shown in Figure 21.

It can be found from Figure 21 that the charge dissipation rate on the insulating medium surface increases with airflow velocity, regardless of whether it is a negative or positive polar charge. At an airflow speed of 10 m/s, the average dissipation rate of positive polar charge is 0.79, and that of negative polar charge is 0.77. At an airflow speed of 60 m/s, the average dissipation rate of positive polar charge is 0.92, and that of negative polar charge is 0.86. This indicates that the amount of charge accumulated on the insulating medium surface decreases as the airflow speed increases. In other words, the amount of charge accumulated on the insulating medium surface is less in the airflow environment than in the no-airflow environment. In addition, it was also found that the polarity of the charge had no obvious effect on the decay characteristics of the charge, and both positive and negative polar charges gradually increased the dissipation rate as the airflow velocity increased; however, the dissipation rate of positive polar charges is faster than that of negative polar charges in the same airflow velocity.

4.3. The Mechanism of Charge Conduction on Insulating Media Surface in an Airflow Environment

The development of an insulating media surface discharge is closely related to the charge density. The dissipation mechanism of the surface charge in the airflow environment will determine the development process of the insulating medium surface discharge. The surface charge of the insulating medium is dissipated in three main ways: (1) through the internal dissipation of the insulating medium; (2) through the surface dissipation of the insulating medium; (3) through the compound action of charged ions in the gas, as shown in Figure 22. The space charge in the insulating medium is mainly concentrated in the surface layer of 1–2 μm on the insulating medium surface; thus, the dissipation of the insulating medium surface charge in the airflow environment is mainly through the compounding with the gas side ions and the insulating medium surface dissipation.

When the insulating medium is in the airflow conditions, the surface of the object and the airflow are violently rubbed due to strong convection, resulting in a rise in the temperature of the surface of the insulating medium. The surface of the insulating medium forms a thermal boundary layer, often called the temperature boundary layer. The airflow moving at high speed will adhere to the surface of the medium due to the adhesion force because of the viscosity of the air. At this point, the kinetic energy is converted into thermal energy, causing the temperature of the insulating medium surface to rise. This phenomenon is called the aerodynamic heating effect in the boundary layer theory.

In order to obtain a more intuitive relationship between the airflow speed and the insulating medium surface temperature, the insulating medium surface temperature at different airflow speeds was measured with an infrared thermograph. Figure 23 shows the surface temperature of the insulating medium at an airflow speed of 50 m/s.

Through extensive testing, it was discovered that as the airflow velocity increased, the insulating medium surface temperature increased accordingly. When there is no airflow, the insulating medium surface temperature is 293 K. When the airflow velocity reaches 50 m/s, the insulating medium surface temperature rises to 304.9 K, which is 11.9 K higher than that without airflow. The air velocity has a great influence on the insulating medium surface temperature, which in turn affects the movement of the insulating medium carriers. The characteristic curve of the insulating medium surface temperature variation with airflow velocity is obtained by fitting, as shown in Figure 24.

The airflow velocity has a great influence on the insulating medium surface temperature, and the change in the insulating medium surface temperature affects the movement of the current carrier. The surface charge of the insulating medium is mainly gathered in the thin layer of the insulating medium. Directional moving airflow makes the gas molecules have certain kinetic energy. When the gas molecules rub against the surface of the insulating medium, the kinetic energy is converted into internal energy, and heat is generated. At the same time, when the gas molecules hit the thin layer of the insulating medium, the gas molecules transfer the energy to the carriers in the thin layer of the insulating medium, such that the carriers in the trap obtain more energy, which increases the probability of the carriers leaving the trap.

The variation curves of trap density with trap energy level at different airflow velocities are obtained by derivation, such as in Figure 25, which shows the distribution curves of deep trap density with trap energy level at different airflow velocities, and Figure 26 shows the distribution curves of shallow trap density with trap energy level at different airflow velocities.

Figure 25 and Figure 26 compare the electron trap energy level distribution characteristics at different airflow velocities. In the absence of airflow, the electron deep trap energy level center and the electron shallow trap energy level center are 0.9331 and 0.8856 eV, respectively. With the increase in airflow velocity, the trap energy level center decreases. When the airflow reaches 50 m/s, the electron deep trap energy level center and electron shallow trap energy level center are 0.8917 and 0.8062 eV, respectively, which are reduced by 4.43% and 8.96%, respectively, compared with the case without airflow.

Through further statistical analysis, the trend curves of the trap energy center at different airflow velocities for the deep trap energy level and shallow trap energy level were obtained separately, as shown in Figure 27.

The curve can be divided into two segments according to the trend of the trap energy center. Section I: At the airflow velocity of 0–10 m/s, this phase of the change is larger and is mainly the insulation medium from no airflow with a change in the airflow environment, such that the insulation medium surface temperature undergoes a sudden change and a sudden increase in temperature, such that the insulation medium surface trap energy level drops. Section II: At the airflow velocity of 10–50 m/s, the electron trap energy level center changes slowly at this stage. As the velocity of the airflow increases further, the rise in temperature is greater, but the rise in temperature also leads to an increase in the conduction band, which slows the downward trend of the trap energy center.

In summary, the action of airflow changes the temperature of the surface of the insulating medium. The higher the airflow velocity, the higher the surface temperature of the insulating medium. The increase in temperature increases the mobility of carriers, decreases the energy centers of deep and shallow traps, and increases the probability of carrier detrapping. Therefore, the insulating medium surface charge is more easily dissipated in the airflow conditions. The rapid dissipation of charge further increases the difficulty of developing a discharge on the insulating medium surface, thus increasing the discharge voltage along the insulating medium surface.

5. Conclusions

In this paper, the surface discharge characteristics of the insulating media in an airflow environment are obtained through experimental research and simulation calculations, which analyze the movement law of surface charge of insulating media in an airflow environment, explores the surface charge distribution and dissipation characteristics of the insulating media in an airflow environment, and reveals the conduction mechanism of surface charge of insulating media in an airflow environment. The main conclusions are described as follows.

(1) The airflow direction and airflow speed have a significant effect on the discharge voltage along the insulating medium surface. When the airflow velocity is in the range of 0–80 m/s, the discharge voltage along the insulating medium surface increases with the increase in airflow velocity. At an airflow velocity of 80 m/s, the discharge voltage along the surface with the airflow direction perpendicular to the needle plate electrode axis decreased by 38.9% compared with the discharge voltage along the surface with the airflow direction parallel to the needle plate electrode axis, which clarified that the discharge voltage along the insulating medium surface in the airflow environment is different in different airflow directions.

(2) In the airflow environment, the discharge path along the insulating medium surface is significantly bent and deflected. The insulating medium discharge region is pulled toward the low field strength region. At the same time, the blow-off effect of electrons and ions reduces the number of electrons and ion concentration in the collisional ionization process, and the deflection and blow-off effect of electrons and ions becomes more obvious with the increase in airflow velocity. The combined deflection and blow-off effects make the occurrence of discharge along the surface of the insulating medium more difficult.

(3) The distribution characteristics of the surface charge of the insulating medium in the airflow environment were obtained experimentally. With the increase in airflow velocity, the insulating medium surface charge spreads gradually along the direction of airflow, which also further reduces the density of the surface charge of the insulating medium. The airflow environment has a traction effect on the charge motion characteristics of the insulating medium surface discharge process, and the airflow traction plays an important role in the deflection characteristics of the insulating medium along the surface discharge development process.

(4) The dissipation characteristics and conduction mechanism of surface charge of the insulating media in an airflow environment are revealed. The dissipation rate of surface charge is accelerated as the airflow velocity increases. The action of airflow changes the temperature of the surface of the insulating medium. The higher the airflow velocity, the higher the surface temperature of the insulating medium. The increase in temperature increases the mobility of carriers, decreases the energy centers of deep and shallow traps, and increases the probability of carrier detrapping.